Pipeline pumping and compression systems a practical approach third edition kamal k. botros - The eb
Kamal K. Botros
Visit to download the full and correct content document: https://textbookfull.com/product/pipeline-pumping-and-compression-systems-a-practic al-approach-third-edition-kamal-k-botros/
More products digital (pdf, epub, mobi) instant download maybe you interests ...
Coabsorbent and Thermal Recovery Compression Heat Pumping Technologies Staicovici
All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher.
I N for MAt I o N C o N tAINE d IN th IS work h AS b EEN obtAINE d b Y thE AMErICAN SoCIEtY of MEChANICAl ENgINEErS froM SoUrCES bElIEvEd to bE rElIAblE. howEvEr, NEIthEr ASME Nor ItS AUthorS or EdItorS gUArANtEE thE ACCUrACY or CoMPlEtENESS of ANY INforMAtIoN PUblIShEd IN thIS work. NEIthEr ASME Nor ItS AUthorS ANd EdItorS ShAll bE rESPoNSIblE for ANY ErrorS, oMISSIoNS, or dAMAgES ArISINg oUt of thE USE of thIS INforMAtIoN. thE work IS PUblIShEd wIth thE UNdErStANdINg thAt ASME ANd ItS AUthorS ANd EdItorS ArE SUPPlYINg INforMAtIoN bUt ArE Not AttEMPtINg to r EN d E r EN g INEE r IN g or oth E r P rof ESSI o NA l SE rv ICES . If SUCh ENgINEErINg or ProfESSIoNAl SErvICES ArE rEqUIrEd, thE ASSIStANCE of AN APProPrIAtE ProfESSIoNAl ShoUld bE SoUght.
ASME shall not be responsible for statements or opinions advanced in papers or . . . printed in its publications [Statement from the bylaws (b7.1.3)].
for authorization to photocopy material for internal or personal use under those circumstances not falling within the fair use provisions of the Copyright Act, contact the Copyright Clearance Center (CCC), 222 rosewood drive, danvers, MA 01923, tel: 978-750-8400, www.copyright.com.
requests for special permission or bulk reproduction should be addressed to the ASME Publishing department, or submitted online at: http://tinyurl.com/p72hgfu
ASME Press books are available at special quantity discounts to use as premiums or for use in corporate training programs. for more information, contact Special Sales at customercare@ asme.org
Library of Congress Cataloging-in-Publication Data
Names: botros, kamal kamel, author. | van hardeveld, thomas, author. title: Pipeline pumping and compression systems: a practical approach / kamal k botros, thomas van hardeveld
description: third edition. | New York: ASME Press, 2018. | Includes bibliographical references and index.
Identifiers: lCCN 2018022199 | ISbN 9780791861783
Subjects: lCSh: Pumping machinery. | Pipelines.
Classification: lCC tJ901 .M57 2018 | ddC 621.6/9--dc23 lC record available at https:// lccn.loc.gov/2018022199
DEDICATION
we dedicate this third edition again to the memory of our dear friend and colleague, dr. Mo Mohitpour, who continues to inspire the two authors of this book to share their knowledge and experience in the pipeline industry.
TABlE Of CONTENTs
3.2.7
3.2.8
3.2.9
3.3.8
3.3.9
5.1
5.2
5.3
5.4
5.5
5.4.7
5.4.8
5.4.9
5.4.10
5.4.11
5.7
5.9
5.9.1
5.9.2
5.9.3
5.9.4
5.9.5
5.9.6
5.9.7
5.9.8
5.10
chapter
6.1
6.2.1
6.2.2
6.2.3
6.2.4
6.2.5
6.2.6
6.2.7
6.2.8
6.2.9
6.2.10
6.4
6.5
6.3.4
6.3.5
6.3.6
6.3.7
6.4.1
6.4.2
7.1
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.2.6
7.2.8
7.3
7.3.1
7.4
7.3.6
7.4.1
7.4.2
7.5.1
7.5.4
8.2.8
8.6.6
PREFACE
the technology of pipeline pumping and compression continues to change, so we decided that it was worthwhile to again spend the time and effort to produce this third edition. In the end, the improvements turned out to be substantial, which makes us grateful to again share our knowledge and experience and that of the industry at large. the reader will find a wide range of topics that are both practical in nature and ones that delve more deeply into the science and engineering basis behind pumping and compression processes. one of the drivers for this edition was its use as the textbook by one of the authors (tom) for a graduate course in Mechanical Engineering at the University of Calgary called Pipeline Pump and Compressor Stations, a part of the Pipeline Engineering Center. In particular, a number of additions were made to enhance the content for this course.
there are no new chapters this time but significant additions include updated information on the pipeline industry, pipeline safety, contamination between batches, design of terminals, booster pumps, pump station design, monitoring of centrifugal compressor degradation, equations of state for gas mixtures, gas turbine auxiliary systems, cold vs. hot recycle surge protection, PSv instability, integrally geared compressors, pulsation and vibration control for reciprocating compressors, damping of mechanically resonant systems, transient analysis of liquid pipeline systems, a more comprehensive introduction to environmental issues and many more topics. we must admit to removing some sections related to gas and liquid hydraulics since these topics are already well covered in a similar publication from ASME, Pipeline design and Construction – A Practical Approach, as well as other industry publications. this enabled the addition of other, more relevant advances in this area.
we have again reached out to colleagues and contacts in the industry and want to specifically recognize the following for their contributions and assistance:
Suzanne wilton – Enbridge Inc. drew devitt – New way Air bearings bill forbes – Enbridge Inc.
vik kohli – Enbridge Inc.
Steve McNair – windrock dr. ron hugo – University of Calgary.
Another improvement that was made was to provide many of the figures in color for the digital edition. Unfortunately, the printed book will still be in b&w so as not to drastically increase its cost but as compensation, many of the figures have been improved in quality.
without ASME, this edition would not have been possible, so we want to particularly acknowledge the continuing support and encouragement of Mary grace Stefanchik and tara Collins Smith of ASME Press.
Again, we deeply appreciate the opportunity to contribute to this important field of engineering and restate that “this is the book I wish I had when I was a young engineer wanting to learn about pipeline pumping and compression.”
Kamal K. Botros
Thomas Van Hardeveld
FOREWORDs
Foreword to the first and second editions from TransCanada Pipelines
Pumping and Compression facilities are critical components of pipeline systems and Pipeline Pumping and Compression Systems—A Practical Approach is a tremendous resource that marks another milestone of excellence and achievement for the pipeline industry.
ASME Press initiated the development and publication of the pipeline series in 2000 with Pipeline Design & Construction—A Practical Approach and a number of excellently detailed and comprehensive pipeline titles since then. this book is in response to the needs of the industry and the community to further augment this series.
the book is a wide-ranging professional reference, training tool, and text covering all aspects of pipeline pumping and compression system design, configuration optimization, installation, commissioning, and operation. It provides practical solutions for dynamic situations encountered in designing pipeline systems to support reliable operation.
the content of this book reflects the considerable knowledge and expertise of the authors. their learnings through eight decades of collective industry experience is supplemented by research and development as well as industry-generated data.
we are very pleased to continue with our support for this series of the ASME books and related efforts made in capturing the knowledge important to our industry.
Andrew Jenkins Vice President, TransCanada PipeLines Limited
Foreword to the first and second editions from GE Oil & Gas
gE oil & gas has supported the preparation, review, and publication of the ASME book Pipeline Pumping and Compressions Systems—A Practical Approach. this timely publication completes the pipeline system design, construction, operation, and maintenance series of books, which ASME initiated in 2000.
Pumps and compressors are key elements in any pipeline transmission project. today, a total of almost 50 million horsepower is used to service natural gas pipeline compression needs; a similar amount of power is used in pumping hydrocarbon liquids through transmission pipelines. Pump and compression units power range roughly between 500 and 45,000 hp, and new designs are increasing this power. there is no doubt that these units’ capability have substantially contributed to increase the size, length, and grade of pipeline networks worldwide.
In the early 1900s, the throughput-to-fuel gas ratio was almost 50:50, whereas for modern day gas compression, the ratio is 94:6. Much of this development has been driven by environmental, operational, and cost implications. these demands for stricter emission controls, lower fuel costs, and higher availability are impacting new equipment purchase and also the decisions to replace older units.
Pipeline Pumping and Compressions Systems—A Practical Approach represents a thorough evaluation and presentation of pipeline pumping and compression needs and development. It serves as a useful guide for the design of such facilities in liquid and gas pipeline transmission systems, as well as a guide to various installation options.
the authors have used their considerable knowledge and experience of the pipeline industry to provide a very useful and practical document not only to augment the knowledge of professionals but also to help to convey the knowledge to new entrants in the industry.
I am pleased that such a comprehensive training and reference tool, covering all aspects of pipeline pumping and compression systems, is available to the industry.
Patrick Campbell, P.Eng. General Manager,
Foreword to the third edition from Dr. Ron J. Hugo
Pipeline Pumping and Compression Systems – A Practical Approach was first published in 2008 in advance of the ASME International Pipeline Conference in Calgary, Alberta, CANAdA. the second edition of this book was published in 2013.
Since the first edition of this book was first published in 2008, the industry has seen the retirement of a generation of experienced pipeline engineers who honed their skills working on complex projects with companies that performed the full lifecycle of an engineering project in-house, beginning with feasibility studies, to design, followed by construction and operation. through the retirement of this experienced generation comes an apparent void. In response, this most recent edition by botros and van hardeveld offers a critical and effective transfer of knowledge. this book provides the new generation of pipeline engineers with a solid foundation upon which they can build their careers.
the evolution of this third edition came about through its use in a graduate course taught by the second author, thomas van hardeveld, and offered through the Pipeline Engineering Centre at the University of Calgary. with this in mind, the book will prove to be equally useful for both the engineering graduate student and the working professional. the collective years of experience of the two co-authors and the founding author in both gas and liquid transmission systems is unmatched, providing the reader with valuable knowledge and insight that has been gained through years of professional practice.
on behalf of the pipeline engineering community, I am grateful to the authors for investing so much of their time to share and give back to their profession. their work provides an inspiration for all professional engineers.
Ron J. Hugo, Ph.D., P.Eng.
Director, Pipeline Engineering Centre
Li Ka Shing Foundation Chair in Engineering Education Innovation
Department of Mechanical & Manufacturing Engineering
Schulich School of Engineering
University of Calgary, 2500 University Dr NW Calgary Alberta Canada T2N 1N4
Chapter 1 introduction to pipeline systems
1.1 IntroductIon
Pipelines affect the daily lives of people in most parts of the world. Modern-day life is based on structures in which energy fulfills a prevailing role. Oil and gas are major participants in this energy supply [1]. The ever shifting trends in forms of energy [2], such as coal, nuclear, hydro-electric, gas, oil and renewables (Fig. 1-1) will continue to dominate energy usage in the future, depending on acceptability, safety, technical, environmental, and economic issues. The rise of renewable types of energy replacing other forms of energy means that hydrocarbons will also be affected although this will be at least partially offset by increasing demand.
However, pipelines are the means by which many hydrocarbon-based forms of energy are transported. It is no coincidence that wherever there is the largest pipeline network, there is also the highest standard of living and technological progress. Compared with other forms of transport, pipelines allow a safer, more continuous, stable, and high-capacity supply of hydrocarbons to reach end-users. Pipeline transportation has the advantages of being well established, efficient, cost-effective, and readily expandable. In spite of claims that pipelines are not safe and environmentally damaging, pipelines have consistently maintained a very high safety record that is superior to other types of hydrocarbon transportation.
Pipeline technology is mature and well understood. The capital cost of a pipeline project is largely a function of its diameter and length, although other factors, such as geography and topography, are also significant. Operating expenditures and self-consumption of product are relatively minor and predictable. Economic feasibility of a pipeline is limited by variables, such as volumes to be transported, supply–demand distance relationships, operating pressure, projected reserve life, and various risk factors. These limitations are more restrictive offshore than onshore.
The relative transportation cost for various petroleum products is depicted in Fig. 1-2. Although pipelines have been the most cost-effective mode of energy transportation, it can be inferred from Fig. 1-2 that cost of energy transportation by pipeline is distance- and location- (offshore versus onshore) dependent [3].
Pipelines are mostly buried. In virtual silence, pipelines supported by pump and compressor stations that carry billions of cubic meters of our energy needs. Unattended pump stations push oil and petroleum products in large volumes and under high pressure. Similarly, natural gas transmission systems supported by compressor stations move large volumes of gas to multiple destinations.
1-1. Trends in primary energy consumption [2].
1-2. Representative costs of oil and gas transportation (US$/MBTU) (Mohitpour et al. [3]).
1.2 LIQuId PIPELInE SYStEM
The liquid pipeline transportation system applies to a variety of liquid hydrocarbons, including crude oil, refined petroleum products, liquid petroleum gas, gas to liquids, anhydrous ammonia, alcohols, and carbon dioxide. Liquid pipelines, including generally consist of laterals and mainlines which include tank farms, measurement facilities, pumping systems, pressure reduction, control systems, and pipeline appurtenances (scraper traps, valves, etc.). As can be seen from Fig. 1-3, pump stations are an integral component of this very extensive network.
Liquid pipelines are used to transport liquids, such as crude and refined oil, from the source of supply, such as a production area, to the market/demand locations, an exportloading terminal, or to a processing unit (a refinery). Mainline pump stations are installed
Figure
Figure
along the transmission pipelines at variable distances to compensate for the pipeline pressure losses and elevation changes and to ensure a constant flow of liquid.
Scopes defining the limit of the pipeline system are well defined by applicable codes, an example of which is shown in Fig. 1-4 [5]. Also included within the scope of the system are:
primary and associated auxiliary liquid petroleum and liquid anhydrous ammonia § piping at pipeline terminals (marine, rail, and truck), tank farms, pump stations, pressure-reducing stations, and metering stations, including scraper traps, strainers, and prover loops; storage and working tanks, including pipe-type storage fabricated from pipe and § fittings, and piping interconnecting these facilities; liquid petroleum and liquid anhydrous ammonia piping located on property which § has been set aside for such piping within petroleum refinery, natural gasoline, gas processing, ammonia, and bulk plants; and those aspects of operation and maintenance of liquid pipeline systems relating to the § safety and protection of the general public, operating company personnel, environment, property, and the piping systems.
Pipeline pumps are used for boosting pressures and for transferring product in both gathering and mainline transmission systems. Centrifugal, reciprocating, and rotary-positive displacement pumps are generally used for such pipeline applications.
In a pump station located on larger transmission lines, usually one or more high-capacity, single, or multi-stage centrifugal pumps are installed. They can be driven most commonly by electric motors usually in the 2–6 MW range but also sometimes by a gas turbine or diesel engine.
Figure 1-3. Liquid petroleum systems from the wellhead to the consumer [4].
Figure 1-4. Liquid pipeline system definitions [5].
A unique aspect of a liquid pipeline system is that the product is pumped from the wellhead into a storage tank. From there, the liquid is carried by a gathering system pipeline (or flowline) to a larger set of storage tanks, also referred to as a terminal. The liquid is then pumped to the next terminal. This process continues all along the pipeline system, a necessary result of the fact that liquids are essentially incompressible.
1.3 GAS PIPELInE SYStEM
Gas is usually considered to be any hydrocarbon-based gas or mixture of gases suitable for domestic or industrial fuel that is transmitted or distributed to the user by a pipeline/piping
pipeline systems
5 system. The most common types are various compositions of natural gas but other gases such as hydrogen and carbon dioxide are becoming more prevalent. A gas transmission and distribution system (Fig. 1-5) consists of the following components:
§ constituents gathering pipeline facilities
gas processing and treatment facilities to remove objectionable materials and
§ production plants/compression
§ receipt meter stations
§ lateral lines
§ mainlines
§ mainline control valves to regulate pressure or flow
§ mainline compression facilities
§ delivery meter stations/custody transfer/city gate stations
§
§ storage facilities used for peaking requirements (usually the pipeline itself)
The components include production wells, gathering lines within the production wells, processing plants, transmission pipelines, compressor stations (periodically along the transmission pipelines), storage wells and associated gathering pipelines, metering stations and city gate at distribution centers, distribution piping, and meters at distribution sites (residential or industrial).
Compression facilities are the heart of gas pipeline systems. Compressor stations transmit natural gas through a pipeline by compressing the gas at intervals along the system. Compressing gas increases the mass flow and increased pressure is necessary to overcome friction and elevation. Gas flows by expanding in the pipe from the discharge side (high pressure point) from one station to the suction side (low pressure point) of the next.
Figure 1-5. Natural gas pipeline systems from the wellhead to the consumer [4].
The use of compression equipment on or related to pipelines covers a wide field, ranging from a small manually operated field compressor up to a large computer-controlled installation involving many thousands of kilowatts. Compression equipment performs one or more of the following major functions with respect to the gas pipeline industry in general:
Transmission. Long-distance mainline transmission is designed with compressor stations spaced at intervals along the pipeline. The compression ratio across a station, resulting from pipeline friction losses and typically ranging from 1.2–1.7, is established by the compressor units as they are placed into operation or varied in load. These stations are usually designed for fully automatic, remotely controlled operation to enable a complete pipeline system to be operated from a central location.
Lateral Compression. Lateral pipeline transmission is designed to carry gas from one or more sources to a main pipeline, or from a pipeline to a sales point or distribution system. Operation varies from base load to “on–off” depending on the situation and can be subject to large changes. Compression ratios are often higher than for a main line station, with flows and power requirements being much less.
Field Compression. Field compression and gas gathering stations involve the boosting of gas field well-head pressures up to a required plant inlet pressure or directly to a pipelineoperating pressure. Compression ratios are often high, with a slowly declining suction pressure (and therefore increasing pressure ratio) as the gas field becomes depleted.
Interchange Compression. Interchange compression is often required to transfer gas between different pipeline systems. The operating conditions include variable suction and discharge pressures, which may vary at random, unaffected by the compressor operation.
Gas Storage Compression. Gas storage compression is designed for injection and withdrawal of gas from peak shaving or storage reservoirs. These compressor units operate under a continually changing compression ratio, both on injection and withdrawal, and would be considered as high-ratio, high-flow, and high-power units.
Booster Compression. Booster compression is designed to raise the pressure from a low pressure transmission line, for example, to a high pressure line. The units would basically be considered as transmission units but operating under higher compression ratios.
Gas Recovery Compression. Gas recovery compression is used to raise associated gas (gas in solution with crude oil) from very low pressures (down to almost atmospheric pressure) up to pipeline transmission pressure. This is a very high-ratio service.
1.4 PIPELInE SAFEtY
1.4.1 Process Safety
1.4.1.1 Process Safety Management (PSM)
Pipeline facilities have an enviable safety record, particularly considering the hazardous products at pump and compressor stations. Accidents or incidents that do occur are usually contained within the facility perimeter with no or limited consequences to the public. In spite of the very low level of risk, pipeline transportation companies are increasingly adopting the process safety management systems that are common in the highly hazardous industries such as petrochemicals and process plants.
Process Safety is a disciplined management approach applied to systems containing hazardous materials. It focuses on the prevention, detection, control and mitigation of catastrophic incidents that have the potential to injure people or could have far-reaching and long-lasting consequences. Process safety is about preventing loss of primary containment (LOPC) of a hazardous commodity and mitigating subsequent impacts to people, environment, assets and reputation. Process safety incidents are extremely rare.
However, their consequences have the potential to be severe (large releases), up to and including company or industry ending impacts. Worker Safety incidents are much more frequent but minor in comparison. Both are important, and all safety incidents must be prevented.
More emphasis on Process Safety Management (as opposed to personal or occupational safety) is being placed with respect to managing risk and hazards in regulations such as OSHA 1910.119 Process safety management of highly hazardous chemicals in the US and the National Energy Board Regulations SOR/99-294 in Canada. While these regulations require programs to be set up for managing risks and hazards, they are not prescriptive as to how this should be accomplished.
To meet this need, the pipeline industry has published more specific guidance in API RP1173 [6] that applies to both pipelines and facilities. The major topics it covers are:
§ Stakeholder Engagement
Leadership and Management Commitment
§ Risk Management
§ Operational Controls
§ Incident Investigation, Evaluation, and Lessons Learned
§ Safety Assurance
§ Management Review and Continuous Improvement
§ Emergency Preparedness and Response
§ Competence, Awareness, and Training
§ Documentation and Record Keeping
§ Further guidance is provided in national standards such as CAN/CSA Z662 [7] and CAN/CSA Z767-17 [8]. There are also industry documents such as the recommended practice on facility integrity [9] by the Canadian Energy Pipeline Association (CEPA). The CEPA Recommended Practice provides a management systems approach in defining a Facility Integrity Management Program (FIMP) with more detail on implementing a practical framework [10]. The main challenge in developing a framework for a FIMP lies in the broad range of equipment and system types that the management system must encompass. Equipment, in the context of Facilities Integrity Management, must encompass not only station equipment (such as rotating equipment, valves, meters etc.,) but also categories such as high pressure station piping and fuel lines.
The broad range of equipment types gives rise to three main parameters that needed to be addressed [9]:
Equipment specific considerations: while fundamental concepts for managing integ-
§ rity are essentially the same across all equipment types, the specific analysis methodologies and tactics will vary widely.
Differing levels of criticality, or risk levels, associated with various equipment
§ types: the criticality of different equipment types should correlate to the resources (both time and budget) dedicated to managing the integrity of the equipment. Widely varying asset life: longer asset life would be expected to correlate with
§ maintenance dollars. Thus, in addition to potentially different time horizons for analysis, an Operator would expect to spend more effort in managing aspects of its system that have more significant cost implications.
1.4.1.2
risk Assessment
A key component of applying Process Safety Management is identifying hazards and analyzing and evaluating risk or risk assessment. Many techniques are available for risk assessment [11] with the most common techniques being:
§ What If/Checklists [11]
Hazard and operability (HAZOP) studies [12]
§ Failure Modes and Effects Analysis [13]
§ Fault Tree Analysis [14]
§
§ bowtie diagrams [15]
A very effective method is the use of bowtie diagrams. Bowtie diagrams are a widely used method for demonstrating the relationship between the causes and consequences of hazardous events. They are particularly useful for illustrating how safeguarding measures protect against particular threats or mitigate the various consequences of an incident. Figure 1-6 presents an example of a bowtie for a leaking flange at a pump station by showing its key features:
Hazard – a potential source of danger. For a pump station, this would be oil in the
§ pipe and for a compressor station, the high pressure natural gas in the main piping. Existence of a hazard does not necessarily imply that an incident will occur.
Top Event – the hazardous event at the center of the diagram. The normal top event
§ for a pump station would be a Loss of Primary Containment (LOPC), in this case a flange leak.
§ flange leak could be a defective flange connection.
Threats – potential causes of the top event, on the left-hand side. One threat for a
Causes – the means by which a threat could result in a tope event. For a defec-
§ tive connection, causes could be a manufacturing defect in the flange or gasket or improper installation.
Prevention barriers – measures in place to prevent threats leading to the top event.
§ Quality inspections at the vendor or during installation could be barriers that would prevent a cause from leading to a flange leak. There is the likelihood of gasket deterioration as a barrier decay mechanism that would suggest regular replacement or monitoring would be appropriate, especially for corrosive liquids.
Mitigation barriers – measures in place to prevent the top event from leading to a
§ more serious consequence. Quick emergency response would be a mitigation barrier and a barrier decay mechanism that would need to be considered is a storage issue with the emergency response equipment.
Figure 1-6. Example of a bowtie diagram for a flange leak at a pump station.
Consequences – potential outcomes of the top event, on the right-hand side. For § a leaking flange, this would be an oil spill, usually contained with the facility perimeter.
Effects – actions that would have to be taken to deal with the consequences. In this § case, oil contamination would result and would have to be cleaned up.
1.4.1.3 operational Hazards and risk
Operational hazards at pump and compressor stations are similar in some cases and vary for others, mainly due to the nature of the fluid being transported. Liquids may be volatile and present the risk of contamination and explosion. Gas may catch fire although it does not normally contaminate since it dissipates easily into the atmosphere.
Centrifugal pumps mostly used in the pipeline industry are for transportation of crude (including heavy) oil—a mixture of liquid hydrocarbons, some with volatile at atmospheric conditions such as condensate. Crude (particularly heavy oil) can be also warm (60–80°C).
Crude oil can also contain contaminants, some toxic such as hydrogen sulfide, radioactive such as strontium salts, or just water or grit. Additives may be introduced which have toxic properties, although these would normally be only in low concentrations. Therefore, hazard and risks associated with the pump operations must be considered and taken care of in the design and selection stage as much as possible.
The hazards associated with a large centrifugal pump must be considered over its complete operating/maintenance cycle. Operating range includes any abnormal and transient situations and loads. Poor operation/excursions/drive system failures and emergencies also are required to be covered.
The majority of hazards relate to the liquid being handled, either by a direct release, or by the consequent effects on upstream and downstream systems from a pump failure:
failure of static components through fatigue, erosion, or corrosion
§ failure of dynamic components leading to high fatigue loads on other components
§ with potentially rapid catastrophic deterioration of seal or nozzles failure of the piping system due to extreme pressures or temperatures—either exter-
§ nally applied or generated by the operating pump or system, resulting from events such as pressure surges, process density, or liquid property changes
The direct threats to personnel from a release can arise from:
§ ponents, which would form a gas cloud with potential for explosion, or fire physical injury from a jet of fluid, or slips/falls from contaminated floor surfaces
the possible flammable nature of fluid released—volatile/high vapor pressure com-
§ liquid which may well be hot, giving a scalding risk above 60–70°C range
§ the liquid which may also evolve asphyxiating gases:
§ the toxic nature of components or additives within process material (liquids con-
• taining hydrogen sulfides are highly toxic)
small traces of radioactive salts within the process material can accumulate
• within a pump requiring appropriate handling precautions inappropriate operation of the pump can induce high temperatures and pressures
• within a pump, giving rise to hazards from mechanical disintegration of the pump handling material with higher concentrations of water or solids which can lead to
• higher pressure generation due to the effective increase in density
Hazards for compressors are due mainly to high pressure and the potential for fire when in a confined space such as the unit building. Piping components are also critical to safety as the weld
failure of a flange on a station gate valve at Princess Compressor Station in Alberta, Canada on February 23, 1980 showed (Fig. 1-7). High voltage electrical components are a hazard for electric units. Hermetic compressors are fundamentally very safe due to their sealed design but, as an incident revealed, the weak point is where the cable supplying the motor is not properly sealed and process gas can leak back into the control building where it can explode as Fig. 1-8 illustrates [16]. It must be remembered, however, that these types of incidents are very rare. Mechanical hazards from improper pump or compressor operation could include:
§ liquid induced vibration—running outside best efficiency point
dynamic instability—vibration leading to bearing and pump component damage
§ over-speed and reverse rotation—mechanically or process-induced
§ internal clearances
§ bearing failure/lubrication
§
§ seal failure
Figure 1-7. Compressor station fire.
Figure 1-8. Compressor station explosion [16].
joint failure
§ loss of piping and pump restraints
§ corrosion
§ erosion
§ failure of connections—overload and fatigue issues
§
§ entrapment from contact with rotating shaft or other similar components
1.4.2 dependability of Pipeline Systems
1.4.2.1
dependability
In today’s competitive and changing environment, it is crucial that pipelines and associated facilities create and sustain value for their stakeholders. This value can only be achieved by incorporating dependability into the pipeline system, in whole or in part. Dependability characteristics address not just availability and reliability as the probability of successful performance, but also identify other potential risk exposures such as degradation and wear-out that advocate the need for maintenance and logistic support to sustain “problem free” pipeline and facility operation. Dependability engineering [17] provides practical means and measurable targets for achieving value, which are then implemented by sound operational risk assessment practices.
The term “reliability” has the specific meaning as the probability that something may fail within a certain time period but is also commonly used in a broader sense for the combined and related concepts of availability, maintainability, supportability, maintenance, safety, integrity, and a host of other terms. This has led to a proliferation of aggregate terms such as R&M (Reliability and Maintainability), RAM (Reliability, Availability and Maintainability), RAMS where the additional “S” is safety, and Dependability, which is used by international standards.
On the international scene, the IEC (International Electrotechnical Commission) established a TC (Technical Committee) 56 in 1967 to address reliability standardization. The initial title of IEC/TC56 was “Reliability of electronic components and equipment.” In 1980, the title was amended to “Reliability and Maintainability” to address reliability and associated characteristics applicable to products. In 1989, the title was changed to “Dependability” to better reflect the technological evolution and business needs on a broader scope of applications based on the concept of dependability as an umbrella term. In 1990, following consultations with ISO (International Organization for Standardization), it was agreed that the scope of TC56’s work should no longer be limited to the electrotechnical field, but should address generic dependability issues across all disciplines. The scope of IEC/TC56 covers the generic aspects on dependability program management, testing and analytical techniques, software and system dependability, life cycle costing and technical risk assessment. This includes standards related to product issues from component reliability to guidance for engineering dependability of systems, standards related to process issues from technical risk assessment to integrated logistics support and standards related to management issues from dependability management to managing for obsolescence.
Dependability provides critical value at the pipeline system level by ensuring that the combination of pipe and pump/compressor stations can provide the capacity and availability to satisfy contractual requirements. For the pipe portion, dependability is normally couched in terms of risk management or integrity management with the objective of public, employee and contractor safety, avoidance of environmental damage, satisfying regulatory requirements and managing cost. For facilities, dependability value is obtained by high availability and reliability and low life cycle costs.
Due to fundamental differences in these assets pipe being a structure and facilities consisting of many types of equipment it is natural that different approaches and techniques are needed to ensure effective and dependable operation over their life cycle.
Dependability is the ability to perform as and when required. It applies to any physical asset such as a system, product, process, or service and may involve hardware, software and
Another random document with no related content on Scribd:
is usually a circular, narrow, white zone between the congested area and the margin of the transparent cornea.
6th. Examine the Membrana Nictitans. See that its free margin is uniformly smooth, even, and thin and that there is no swelling, congestion nor morbid growth on any part of the structure.
7th. See if the transparent cornea is perfectly and uniformly smooth, transparent and glistening and if it reflects clear, erect images of all objects in front of it. The image of a round object which shows any irregularity in the curvature of its margin implies a deviation from an uniform curvature of the cornea: the image narrows in the direction of the smaller arc and broadens in the direction of the larger one (see keratoscopy, and corneal astigmatism).
8th. A foreign body on or in the cornea may be recognized in a good light, but better and more certainly under focal oblique illumination (see this heading).
9th. A corneal ulcer may be similarly recognized. It is made more strikingly manifest by instilling into the lower cul de sac a drop of a solution of fluorescin and rubbing it over the eye by moving the eyelids with the finger. This will stain the whole cornea. If now the excess of stain is washed away by a few drops of boric acid, the healthy part of the cornea is cleared up and the ulcer retains a bright yellowish green tint.
10th. Opacity or Floating objects in the aqueous humor (flocculi of lymph, pus, pigment, blood, worms) are always to be looked for. They may be detected by placing the eye in a favorable light. They may be still more clearly shown under focal illumination (see below).
11th. Changes in the iris and pupil may also be noticed in a good light. The surface should be dark in the horse, and of the various lighter shades in the smaller animals, but in all alike clear, smooth and polished, without variation of shade in spots or patches and without bulging or irregularity at intervals. Apart from the congenital absence of pigment in whole or in part, which may be found in certain sound eyes, a total or partial change of the dark iris of the horse to a lighter red, brown or yellow shade implies congestion, inflammation, or exudation. The corpora nigra in the
larger quadrupeds should be unbroken, smooth, rounded, projecting masses outside the free border of the upper portion of the iris. It should show a clear, polished surface like the rest of the iris. The pupil should be evenly oval with its long diameter transversely (horse, ruminant), circular (pig, dog, bird), or round with an elliptical outline on contracting and the long diameter vertical (cat). It should contract promptly in light and dilate as quickly in darkness. Place the patient before a window, cover one eye so as to exclude light, then cover the other eye with the hand and quickly withdraw. The pupil should be widely dilated when the hand is withdrawn and should promptly contract, and it should actively widen and narrow alternately until the proper accommodation has been secured. Any failure to show these movements implies a lesion in the brain, optic nerve, or eye which impairs or paralyzes vision, interferes with accommodation or imprisons the iris. In locomotor ataxia the pupil contracts in accommodation to distance, but not in response to light.
12th. Other causes of pupillary immobility include: (a) Permanence of a pupillary membrane, which has remained from the fœtal condition and may be recognized by oblique focal illumination and invariability of the pupil: (b) Adhesion of the iris to the capsule of the lens—complete or partial—in the latter case the adherent portion only remains fixed, while the remainder expands and contracts, giving rise to distortions and variations from the smoothly curved outline: (c) Adhesion of the iris to the back of the cornea— complete or partial—and leading to similar distortions: (d) Glaucoma in which intraocular pressure determines a permanent dilatation of the pupil and depression of the optic disc: (e) The pupil is narrowed in iritis, and is less responsive to atropia or other mydriatic: (f) Lesions of the oculo-motor nerve may paralyze the iris and fix the pupil. The first three and the fifth of these conditions may be recognized by the naked eye, alone, or with the aid of focal illumination, the fourth may require the aid of the ophthalmoscope and the sixth which cannot be reached by such methods, might in exceptional cases be betrayed by other disorders of the oculo-motor nerve (dropping of the upper eyelid, protrusion of the eyeball, squinting outward).
13th. Coloboma (fenestrated iris), and lacerated iris are recognizable by the naked eye in a good light, or by the aid of focal
illumination.
14th. Tension of the eyeball (Tonometry). Elaborate instruments constructed for ascertaining ocular tension are of very little use in the lower animals. The simplest and most practicable method is with the two index fingers placed on the upper lid to press the eyeball downward upon the wall of the orbit using the one finger alternately with the other as if in search of fluctuation. The other fingers rest on the margin of the orbit. All normal eyes have about the same measure of tension and one can use his own eye as a means of comparison. The educated touch is essential. In increased tension, the sense of hardness and resistance, and the indisposition to become indented on pressure is present in the early stages of internal ophthalmias (iritis, choroiditis, retinitis), phlegmon of the eyeball, glaucoma, hydrophthalmos, and tumors of the bulb.
Oblique Focal Illumination.
This is so essential to clear and definite conclusions and is so easily practiced on the domestic animals that every veterinarian should make himself familiar with the method. The method is based on the fact that when two perfectly transparent media touch each other a reflection of luminous rays takes place only at the surface. But in case any opacity exists in any part of the thickness of one of these media, it reflects the rays from its surface no matter what may be its position in the medium. Thus corneal opacities appear as gray blotches and under careful focal illumination it may be determined whether these are on the conjunctival surface, in the superficial or deeper layers of the cornea or in the membrane of Descemet. Similarly cloudiness or floating objects in the aqueous, reflect the luminous rays, and so with opacities in the lens or its capsule, or in the vitreous. In the same way the surface of the iris and corpora nigra may be carefully scrutinized. For satisfactory examination of the media, back of the iris, the pupil should be first dilated, by instillation under the lid of a drop or two of a 3 per cent. solution of atropia, and the examination proceeded with twenty minutes later. Homatropin is preferable to atropin as being less persistent in its action, and less liable to produce conjunctivitis. If it fails to produce the requisite dilatation, it may be followed by a drop of a 4 per cent. solution of hydrochloride of cocaine, which will secure a free dilatation, lasting only for one day in place of seven days as with atropin. The cocaine further removes pain and favors the full eversion of the eyelids.
The instruments required for focal illumination are a biconvex lens of 15 to 20 diopters, and a good oil lamp or movable gas jet. The light of the sun is not satisfactory. The examination ought to be conducted in a dark room, or less satisfactorily in semi-darkness. The lamp is held by an assistant at the level of the eye to be examined, either in front or behind, or first one and then the other, so that the rays of light may fall upon the eye obliquely. If the lids are kept closed it may be necessary to expose the cornea by pressing on the lids with the finger and thumb. The light is held 8 or 10 inches from the eye and the lens is interposed between it and the eye and moved nearer and
more distant until the clearest illumination has been obtained of the point to be examined. In this way every accessible part of the eye may be examined in turn. The examiner may make his results more satisfactory by observing the illuminated surface through a lens magnifying three or four diameters. It is important to observe that the eye of the operator must be in the direct line of reflection of the pencil of light.
Cornea. By focusing the light in succession over the different parts of the surface of the cornea, all inflammations, vascularities, opacities, ulcers, and cicatrices will be shown and their outlines clearly defined. By illuminating the deeper layers of the cornea proper, the lesions of keratitis, opacities, ulcers and cicatrices will be shown. To complete the examination of the cornea the light should be focused upon the iris so that it may be reflected back through the cornea. This will reveal the most minute blood-vessels, any cell concretions on Descemet’s membrane, or any foreign body in the cornea which may have been overlooked.
Aqueous Humor. Unless the cornea is densely opaque, the anterior chamber can be satisfactorily explored by the oblique focal illumination. The cloudiness or milkiness of iritis or choroiditis furnishes a strong reflection from its free particles of floating matter, its blood and pus globules, and its flocculi of fibrine. The latter have usually a whitish reflection, the blood elements a red (hypohæma), and the pus a yellow (hypopion). The writhing movements of a filaria scarcely need this mode of diagnosis. Sometimes, and especially in the horse, detached flocculi of black pigment are found floating free in the aqueous and are highly characteristic.
By this illumination one can easily determine the distance of the cornea from the iris and lens (depth of anterior chamber) which is lessened by the forward displacement of iris and lens in undue tension in the vitreous (glaucoma, retinitis, tumors, bladderworms), or of the iris alone, in irido-choroiditis with accumulation of exudate in the posterior chamber of the aqueous. The depth of the anterior chamber may increase in cases of luxation or absence of the lens or softening and atrophy of the vitreous.
The adhesion of the iris to the back of the cornea may be satisfactorily demonstrated by focal illumination.
Iris. The lesions of the iris are exceedingly common in connection with recurring ophthalmia in the horse, and examinations in the intervals between attacks are of the greatest importance. The eye should be examined as already stated, at a window or door, and if available by the aid of a mirror. Any changes in form or color, or luster should be carefully noted, any tension of the eyeball, or angularity of the upper lid, and any slight blue opacity round the margin of the cornea. Then the prompt or tardy response of iris and pupil to light and darkness must be made out. To complete the test the eye should be treated with homatropin for three-quarters of an hour and with cocaine for ten or fifteen minutes, and then subjected to oblique focal illumination.
With partial posterior synechia the rest of the pupil is found dilated while the attached portion extends inward remaining fixed to the capsule of the lens. If the synechia is complete no dilatation whatever has occurred. The edges of the adherent iris extend inward as adherent projections, and any exposed portion of the lens is likely to show black points, the seat of previous adhesions that have been broken up. In such cases the periphery of the iris bulges forward from the accumulation behind it of aqueous humor or inflammatory exudate which cannot escape. The discoloration of the iris as the result of inflammation, stands out more definitely under the fuller illumination.
Crystalline lens. In exploring the crystalline lens or its capsule for opacities (cataracts) oblique focal illumination can be employed to the very best advantage, if the pupil has first been widely dilated by homatropine and cocaine. The light is concentrated on all parts of the anterior capsule in turn, then in succession on the different layers of the lens at all points and finally on the posterior capsule. The striking reflection from any points of opacity whether pigmentary, gray or pearly white is diagnostic, not only of cataract, but of its exact position—anterior or posterior, capsular or lenticular.
Purkinje-Sanson images. If the flame of a candle is passed in front of the eye, at a suitable distance, in a darkened room, and the observer looks into the eye obliquely from the opposite side, he observes three images of the flame, reflected respectively from the front of the cornea, from the anterior surface of the lens and from the back of the lens. The image from the cornea is erect, bright and
clearly defined: that from the front of the lens is still erect, but larger and dimmer, because the difference between the index of refraction of the aqueous and lens is very slight: the third image, which is smaller and clearer than the last, is inverted, because the surface of reflection on the back of the lens acts as a concave mirror. The beginner may at first find it difficult to make out the image from the front of the lens but with a little care he can do so, and then by moving the light he should cause each image to pass over all parts of the reflecting surface in turn. Any unevenness or opacity at any point of the reflecting surface, will cause the image reflected from it to become blurred or diffused as it passes over it and thus, not the existence only, but the exact seat of such opacity is easily demonstrated. Opacities on the cornea cause blurring of the bright, erect image of the flame as it passes over that part: opacities on the anterior capsule of the lens blur the dim, erect image when passed over them: finally, opacities in the body of the lens or on its posterior capsule, blur the small inverted image as it passes over them.
Add to this method the oblique focal illumination and the images of the flame reflected from the three mirror surfaces (cornea, anterior and posterior lens surfaces) are made much clearer and more distinct than in any other way. To do this effectively the convex lens should be held so as to focus the flame in the air nearly in front of the cornea. The Purkinje-Sanson images are made very definite and clear. If the lens is approached nearer to the eye so as to throw the image of the flame within or behind the lens, a gray phosphorescent streak of light is seen in the depth of the pupil. This is due to the laminated structure of the lens as well as to the fact that the lens itself is not perfectly transparent even in its normal condition. The absence of the lens or its dislocation and displacement downward, below the line of vision may be inferred from the absence of this gray luminous reflection under this test.
OPHTHALMOSCOPE.
Principle of ophthalmoscope: Angle of incidence and angle of reflection in same line, light close to one side of the eye, reflected into it by a mirror, having a hole in the centre for eye of observer. Opacities show a dense white in transparent media: if in front of lens move with rolling of eye: if behind in opposite direction. To see fundus must use biconvex lens. Emmetropic eye: myopic: hypermetropic. Static refraction. Mydriatics: Atropine, homatropine, daturine, duboisine, hyoscyamine.
In the healthy eye, the pupil and iris, and in cataract, even the opaque anterior capsule of the lens, can be clearly seen. The reflection of the pupil, however, is dark and no object back of the iris can be observed. The reason of the difference is that the rays of light, entering through the whole cornea, are reflected at the same angle at which they strike the surface of the iris. The angle of incidence is the same as the angle of reflection. In the hollow fundus of the eye, however, the light entering through the narrow pupil, strikes the fundus at a point which is hidden from the observer, behind the iris, and being reflected by the concave fundus, in exactly the same line along which it entered, it remains invisible. To illuminate the fundus of the eye, for the observer, his line of vision must be made exactly the same as that in which the pencil of light enters the fundus. This is best effected by reflecting the light into the eye by the aid of a small plane or concave mirror having a hole in the center through which the observer looks into the pupil. The concave mirror gives the stronger illumination, but the plane article is more easily manipulated and tends to cause less active contractions of the pupil. This is the simplest form of ophthalmoscope. For careful examination of the fundus of the eye, it is best to have the subject in a dark chamber, with a single large flame of an oil lamp or gas (electric light with an obscure globe may answer). The light is held behind and on the same side as the eye to be examined, at the level of
the eye and the perforated mirror and the eye of the observer are kept from 10 to 20 inches in front of the eye and also at the same level. For the horse or ox under favorable conditions in a stall, the light of day coming from a fansash over the door may serve the purpose. Nicholas assures us that it may be accomplished even under the shadow of a shed or a tree. In such a case it is better not to have too much glare of light as the reflection from cornea and lens may prevent accurate observation. A somewhat cloudy day may therefore prove advantageous.
In focusing the reflected light on the cornea, and then on the pupil and lens, any opacities in these will be shown as a grayish nebular reflection or a denser white according to their degree of opacity. The opacities in the cornea or aqueous, in front of the axis of vision in the lens move in the same direction and to the same degree as the eye rolls, while opacities on the posterior capsule or in the vitreous, move in a direction opposite to the motions of the eye, and to a degree corresponding to their distance back of the lens. Thus if the eye looks downward such opacities move upward; if it looks upward they move downward; if it looks inward they move outward; and if it looks outward they move inward.
To secure an image of the fundus of the eye, including the entrance of the optic nerve (optic papilla), the tapetum, the pigmentary surface and retina and vessels, accommodation must be made for the normal refraction of the eye of the patient, and even for that of the observer.
In the emmetropic (normal) eye, the rays leave the surface of the cornea parallel to each other and it may be possible for the observer to secure a good image on his retina, without the aid of lenses. In the myopic (short sighted) eye they assume a convergent course on leaving the cornea, and to secure a satisfactory image a biconcave or plano-concave lens must be interposed between the cornea of the patient and the eye of the observer.
In the hypermetropic (long sighted) eye, the rays diverge in leaving the cornea of the patient, and a convex lens must be interposed between this and the eye of the observer, in order that the rays may be focused on the eye of the observer.
To adapt the vision to the different eyes the modern ophthalmoscope is furnished with a series of lenses concave and
convex, any one of which can be moved behind the hole in the mirror to suit the demands of the particular case.
To make a satisfactory examination the pupil should be dilated as for oblique focal illumination. A 1:200 solution of apomorphia may be instilled into the eye (a drop or two) and in 20 to 25 minutes a satisfactory dilatation will have been secured. The effect of the homatropin will usually have disappeared in twenty-four hours.
Determination of Static Refraction.
This can be best done in the lower animals by determining the strength of the lens required to render clear the image of its fundus. By knowing the refracting power of the lens, we may ascertain what deviation from the normal refraction there is in the eye under observation.
In making this test the mirror of the ophthalmoscope must be brought closely to the eye of the patient—1 to 2 inches.
If in such a case and without the use of any lens a distinct image of the fundus is obtained, and if this is rendered less distinct by interposing the lowest convex lens in front of the eye of the observer, the eye is emmetropic.
If the ophthalmoscopic mirror without a lens gives an indistinct vision of the fundus, and if the image is rendered clear by interposing one of the convex lenses, the eye is hypermetropic. The strength of the convex lens, +1, +2 or +3, dioptrics will give the measure of the hypermetropia.
If, on the contrary, the ophthalmoscopic mirror gives an indistinct image of the fundus, which is rendered even more indistinct by the interposition of a convex lens, but is cleared up and rendered definite by a concave lens, the patient is myopic. The strength of the concave lens used will give the degree of myopia, –1 dioptric, –2 dioptrics, etc.
The tendency in the horse is constantly to slight long-sightedness, but the deviation is rarely found to be serious either in this direction or in that of astigmatism.
Mydriatics.
Dilation of the pupil by mydriatics (mydriasis dilation of the pupil) is a most important means of diagnosis, and therefore a knowledge of the action of the different mydriatics is essential. The mydriatics in common use not only dilate the pupil, but also paralyze the ciliary body and the power of accommodation in ratio with the strength of the solution employed. This determines an adaptation of the eye to the farthest point of vision and holds it there until the action of the mydriatic passes off and normal power of accommodation is restored. In short it renders the subject long sighted, during its action.
Atropine the alkaloid of atropa belladonna is the most generally available and persistent of the mydriatics, and is in most common use. It is usually employed as sulphate of atropine, though some prefer the nitrate, the salicylate or the borate to obviate the danger of atropinism. This form of poisoning may show in the occurrence of conjunctivitis and in case of one attack the susceptibility to atropine is greatly to be dreaded, so that it should never again be used on the same subject. The real cause of atropinism is uncertain, it has been variously ascribed to too great acidity or alkalinity, or to microorganisms growing in the solution. Hence the importance of using the antiseptic salts of atropine, and of testing the solution to see that it is exactly neutral before it is applied.
The strength of the solution of atropine is an important consideration. Donders found that 1:120 of water produced a full effect, while Jaarsma obtained the full effect in one hour from a drop of a solution of one to twelve hundred of water. The action on carnivora (dogs and cats) is equivalent to that on man, while on the herbivora (rabbit, horse, ox, sheep) it is somewhat less, and on birds very slight indeed. On diseased eyes a large amount may be required, and with synechia (adhesion of the iris to the capsule of the lens) dilatation may be impossible. The full effect may last 24 hours, and accommodation may remain very imperfect for 11 days.
The direct action of atropine on the eye is shown in dilatation of the pupil of the frog after the eye has been detached from all connection with heart or brain, by excision. It acts also in the normal system through reflex nervous action, since, after division of the sympathetic trunk going to the eye, that eye does not dilate so much under atropia as the opposite eye.
Atropine is usually employed by lodging a drop in the pouch of the conjunctiva (inside the lower lid), and from this it makes its way into the aqueous humor, for if that liquid is transferred to the conjunctiva of another animal it causes dilatation. Puncture of the cornea with evacuation of the aqueous humor lessens the action of the atropine. Atropine dilatation is increased by following it with cocaine which causes contraction of the iridian vessels, the antithesis of the dilatation of the vessels which occurs when the cornea is perforated and the pressure of the aqueous humor is removed.
Atropine is one of the most potent poisons and must be used with caution especially in the carnivora and omnivora. The danger lies not alone in the absorption from the conjunctiva, but also from the escape of the liquid through the lachrymo-nasal duct, to the nose and later to the actively absorbing mucosæ of the lungs and stomach.
The symptoms of general poisoning are: rapid pulse, vertigo, weakness of posterior limbs, general prostration and thirst or dryness of the throat.
Homatropine is an oily liquid produced by the action of muriatic acid on the cyanate of atropine. With hydrobromic acid it forms a readily crystallizable salt, the solution of which acts on the eye like atropine, but more promptly and transiently. One drop of a solution of one to one hundred and twenty, usually gives in twenty minutes, full pupillary dilation and complete paralysis of accommodation which lasts only for twenty-four hours. Add to this that there is little danger of constitutional disturbance and poisoning, and homatropine must be accepted as a more desirable agent than atropine. It is especially to be preferred in cases of senility with shallow anterior chambers, and in glaucoma, in which atropine tends to aggravate the lesion.
Daturine, the alkaloid of datura stramonium is a potent mydriatic, causing pupillary dilatation in a solution of one to one
hundred and sixty thousand of water. It appears to be identical with atropine.
Duboisine the alkaloid of duboisia myoporoides is also a potent mydriatic. Jaarsma found that a solution of the sulphate, of one to three thousand, paralyzed accommodation for twenty-four hours. It acts more promptly than atropine but is more poisonous.
Hyoscyamin, the alkaloid of hyoscyamus niger, is also strongly mydriatic. One drop of an one to three hundred solution of the sulphate paralyzed accommodation for from seventy-five to one hundred hours. Risley found it to act more promptly than atropine, and to be less dangerous than duboisine.
WOUNDS OF THE EYELIDS.
Traumas: bites, lacerations, blows, penetrating wounds, gunshot, scratches, kicks. Upper lid or commissure. Reparatory power of eyelid. Danger of distortion. Treatment: sutures, plaster, shellac, collodion, gelatine, Frick’s gelatine, birdlime, sterilisation: Quilled and twisted suture. Position in stall. Metallic guard for eye.
Causes. Traumatic injuries of the eyelids are especially common in the horse mainly because of his exposure in connection with the services required of him. In a team he is liable to be bitten by one of his fellows, or the lid may be caught on nails, in turning, or on hooks upon harness, chains or wagons. It is sometimes injured by a blow from a club or whiplash, or by knocking the head against solid objects that he failed to see on account of the blinds. Again the injury will come from running against prongs of bushes or trees, or of stump fences. Occasionally a blow with the horn of an ox or cow is the cause, but this is much more frequent with the bovine races. Then again gunshot wounds are found in all animals. In sheep the eyelids sometimes suffer from bites of dogs, while in dogs and cats, the teeth and claws are the main causes of injury. These smaller animals also suffer from brutal blows and kicks.
Nature. Wounds of the eyelids almost invariably affect the upper lid, because of its extra size and prominence. Sometimes one commissure or the lower lid is the injured part.
Clean incised wounds are rare, while lacerations with or without contusions are the common experience. The laceration often extends through the free margin of the lid, and then to one side, mostly the outer, in a direction more or less parallel to the tarsus. The result is that the detached flap drops downward exposing a greater or less portion of the bulb covered with blood. The conjunctiva, the cornea, the sclerotic or iris may be implicated in the lesion in different cases,
so that such wounds are of the most varied degree of gravity. If, however, the lesion is confined to the lid, and in the absence of absolute detachment of the flap, or severe contusion, a good repair may be confidently hoped for. The vascularity and reparatory powers of the eyelid are unusually great, and the looseness of the skin, connective tissue, mucosa, and even the muscles is such that they do not draw injuriously upon the edges of the wound to disturb the process of cicatrization. If the two opposing ends of the divided tarsal cartilage are kept in accurate opposition, the elasticity of his structure serves to preserve the even contour of the palpebral margin, and the adhesion or granulation process between the edges of the wound, soon becomes firm enough to prevent further displacement. Even when one-half of the eyelid is torn loose, remaining attached only by a narrow portion, reunion without any unsightly distortion is not to be despaired of. In case of a mere vertical laceration on the other hand, the case is very simple and hopeful. Even when a portion of a lid has been completely torn off and lost, the loose textures of the remaining part, often appear to stretch in the process of healing so that a fairly serviceable, though by no means an æsthetic covering for the eye may remain. This may serve for a common work horse, but the unsightliness would necessarily debar him from use in a carriage or as a saddle horse. The imperfect protection too, exposes the eye to rainstorms, hail and snow, as well as to dust, and greatly predisposes to conjunctivitis.
Treatment. One can trust implicitly to the extraordinary reparatory power of the eyelids, yet so unsightly is any distortion of these parts, that the greatest pains must be taken to obviate loss of substance, or unevenness or puckering in healing. The points to be mainly sought for are the perfect coaptation of the divided edges, and the restraining of the patient from interrupting the healing process and breaking loose the forming adhesions, by rubbing the eye.
Inconsiderable wounds of the skin may be simply stitched together with sterilized catgut. Then the intervals between the stitches may be approximated, dried, and covered with strips of sticking plaster, or with shellac, collodion or gelatine. Frick’s gelatine is made by dissolving fine gelatine in a 1 per cent. solution of corrosive sublimate and adding about 10 per cent. of glycerine, perfecting the admixture by the aid of heat. When wanted for use it may be melted
by heat and applied on the skin with a camel’s hair brush. Bird lime may be used as a substitute. Sterilization must be sought by the use of sublimate lotion 1:2000, or boric acid 2:100. Formerly the edges were kept in close opposition by the use of quilled sutures, the stitches passed around the quills being inserted at the usual distances while the quills, applied against the edges of the wound kept them smooth and even and obviated puckering. Or, perhaps better, the twisted suture may be employed, the edges being brought together by pins placed close together and a silk thread carried around each in figure of 8, and spirally from pin to pin along the entire length. If one pin comes out it ought to be promptly replaced and the whole left in place until a firm adhesion is established. The points of the pins are cut off short so that there may be no risk of their pricking.
With any method the horse or ox may be turned in his stall so that his tail may be toward the manger and his face outward, and he may be tied by two halters to the two posts, right and left. His food may be furnished in a sack hung from the ceiling and cut down one side. In this way the animal may be absolutely prevented from rubbing the itching sore against any solid body, and thereby interrupting the healing process. Another method is to apply a hood of stiff material with a metallic guard for the face, having bars extending from above downward and arched outward so that they shall effectually protect the eye in any attempt at rubbing.
DEFICIENCY OF THE EYELIDS. COLOBOMA PALPEBRARUM.
The term coloboma representing merely a hiatus or deficiency is applied to different parts of the eye according as there may be a lack of substance of the part in question: Coloboma palpebrarum (deficiency of the palpebræ or lids), C. iridis (perforation of the iris), and C. choroideæ (partial absence of the choroid).
Coloboma palpebrarum is usually congenital and takes the form of a vertical notch on the upper lid, separating its two lateral parts into independent flaps. According to the breadth and depth of the notch are the extent of the exposure of the bulbar conjunctiva and the liability to irritation and infection by foreign bodies. The same condition of things will occur traumatically and require identical measures of repair. These consist in paring the edges of the notch and bringing them accurately together with catgut, silk or quilled suture, the approximation being rendered more perfect by the application of collodion, shellac or gelatine mixture (see wounds of eyelids). The vascularity and extensibility of the tissues of the lids greatly favor a kindly healing. Rubbing of the eye must be guarded against as advised under wounds of the eyelids.
ORGANIC UNION OF THE EYELIDS.
ANKYLOBLEPHARON. NARROWED FISSURE
BETWEEN THE LIDS. BLEPHAROPHYMOSIS.
Complete closure of the palpebral fissure has been seen as a congenital infirmity in sheep, dogs and cats, while the partial closure has been found in all classes of animals as the result of chronic conjunctivitis and contraction of the exudation in undergoing organization. Narrowing of the fissure gives the appearance of a small eye, so that a progressive diminution is usually supposed to come from a reduction in size of the bulb, though no actual atrophy of that organ has taken place. In drooping of the upper lid (ptosis) too, the fissure is reduced and the illusion of an atrophy of the eyeball is induced. The closure of the fissure may come from blepharospasm, as the result of irritants in the eye, or even of nervous disorder.
Treatment. In case of complete closure of the palpebral fissure, the skin is picked up with forceps and an incision is made between the two tarsi into the conjunctival sac. Then with probe pointed scissors, or a grooved director and bistuory the incision is carried between the tarsi to the proper position for the internal and external canthi. During healing the lids should be frequently bathed with a boric acid solution, and an ointment of the same with vaseline should be applied to prevent adhesion.
When the trouble consists in a drawing together of the skin at the outer canthus, the result of inflammation, the adhesions are separated by a horizontal incision leading outward from the line of the angle. The edges of the conjunctiva and skin are then sutured together, so as to prevent further adhesion and the part treated as an ordinary wound. This is known as canthoplasty.
Ptosis coming from tumors on the lid, or excess of fat in its substance, or from oculo-motor disease must be treated according to indications. The same remark applies to spasm of the orbicular muscle (blepharospasm), whether clonic or tonic. In domestic animals the removal of the cause (foreign body, eyelash), will usually succeed.
