Compressor Best Practices Unplanned Loss Working Group
Version 1.0 First draft to share for industry comments
March 2014 Aberdeen, UK
Table of Contents 3
INTRODUCTION SECTION 1:
SCOPE
SECTION 2:
EIGHT BEST PRACTICES FOR EFFECTIVE COMPRESSOR MANAGEMENT
A. UNDERSTAND THE ISSUES
4-5 6-13
6
1. Ensure that your compression system is appropriate for its application today 2. Make monitoring the basis of your maintenance programme 3. When things go wrong ensure you (as an organization) address the root causes B. GET THE BASICS IN PLACE
11
4. Ensure your “inputs” are clean 5. Give more priority to ensuring your ancillaries are in good condition C. ALIGN YOUR PEOPLE TO DELIVER
13
6. Make sure you have one person you can point to who owns the “compressor system” and has all the levers to improve it 7. Ensure your organization has a culture of prioritization and getting the basics right 8. Don’t overlook efficiency SECTION 3:
A STRUCTURED WAY TO INVESTIGATE COMPRESSOR ISSUES
CONTACTS
2
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15
Introduction Compressors have been identified as a major source of losses - data from selected North Sea operators showed that compressors are the 2nd biggest loss category. If these numbers are representative of the industry as a whole, then compressors account for around 66 kboed of losses in the UK North Sea, representing over $2 billion in lost revenues.
Top Losses Per Source Of Loss (-10% Sample of North Sea Production) % of total losses
3rd Party / external 19%
15% Others
Compressors
41%
9% Tanks / vessels 9% 7% Wells Power generation Source: Data from selected North Sea Operators; SBC analysis
As a part of the cross-industry effort to improve production efficiency, Oil and Gas UK has declared that 2014 must be “the year of solving compressors”. This document has been produced by the Unplanned Losses Working Group (ULWG) (Chevron, Schlumberger Business Consulting, Talisman Sinopec Energy, and Taqa) based on front-line learnings of addressing compressor issues, in the UK North Sea and elsewhere. Its intended audience is compressor operators and maintainers, operational managers, and rotating equipment specialists. The ULWG has also produced a higher-level accompanying document “Compressors for Managers”. Section 1 of this document examines the scope of the compressors issue. Section 2 then outlines 8 best practices for effective management of compressors to avoid losses. And, finally, Section 3 provides a structured set of questions to identify compressor problems and their causes.
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3
Section 1: Scope The Compression System Whilst many production losses find themselves allocated to the “compressor� category, they are often the manifestations of problems in the wider compression system: for example, the driver or prime mover; or ancillary equipment such as coolers, fans, separators/ knock-out vessels, lube oil systems, fuel gas systems, seal gas systems, couplings, gearboxes and even slug catchers. Indeed there is strong evidence to suggest that a significant part of the answer to our compression problems is to keep such ancillary equipment in good condition. Consequently, it is important to focus on the compression system rather than just the core compressor itself: to improve performance of the compressor, we must also consider the components and systems listed above.
What types of compressor (and driver) does this document cover? Whilst this is not a document about compressor selection for system designers, compressor selection guidelines give some useful insights. The diagram below shows which types of compressors are generally selected for a range of flow rates and discharge pressures and is taken from a design guideline.
100,000 Rec
ip.-
mu
lti s
e
10,000 r. nt Ce ul
m
Centr. single stage
ti e
ag
st
DISCHARGE PRESSURE, psig
tag
1,000
Recip. single stage
Rotary-screw
100 Rotary-liquid ring Axial
Rotary-straight lobe
10 Rotary-sliding vane
1 1
10
102
103
104
105
106
INLET FLOW, acfm
In general, centrifugal compressors are used for high flow applications, and reciprocating compressors are better suited to low flow rates. In recent years, the use of rotary screw compressors has increased for applications with lower discharge pressures and flows. The chart below shows the proportion of compressor types (by number) for one company’s portfolio, showing that their most common type is centrifugal. Since centrifugal compressors also tend to be bigger, the proportion of losses from this type of compressor is likely to be proportionally higher than the pie chart would suggest.
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Proportions by Application & Type Axial Refrig
Screw 3%
9%
Plant gas
9%
3%
Export 9% Recip 12%
Gas lift & Exp
24%
9% 21%
Fuel gas
76% Centrif
Gas lift
However, at least one other operator does not operate any centrifugal compressors in the North Sea and uses mainly reciprocating. Now, let’s consider some of the big ancillary items. The most important one is power. In terms of drivers, gas turbines (GTs) come into their own as compressor power requirements increase. GTs seem usually to be used above around 7MW and electric motors below (although there is a cross over range). This, and the compressor characteristics chart shown above explains why gas turbines are frequently used to drive centrifugal compressors and electric motors to drive reciprocating designs. The most common configuration for higher flow compression systems – the ones that lead to the largest losses when they fail – is therefore GT driven centrifugal compressors. Consequently this document has a stronger focus on this configuration (although many of the recommendations apply to other compressor types too).
Implementation The objective of this document is to help understand the issues and therefore allow solutions to be identified. It goes without saying that if no solutions are implemented there will not be an improvement in performance. There have been examples of intentions to implement compression improvements but other priorities take precedence and the work is delayed, for years in some instances. In order for improvements to be made across the whole range of losses, it is essential that companies have the systems to identify losses, the capabilities to prioritize the most important ones to fix (and to prioritize these against improvement opportunities), and the execution capacity to deliver. Otherwise, all these improvements will remain at the bottom of the maintenance ticket, never delivered. This is a much wider and more complex issue, beyond the scope of this document.
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Section 2: Eight best practices for effective compressor management This section presents eight best practices for compressor management. They are grouped in three themes:
The compressor best practices can be divided into three themes UNDERSTAND THE ISSUES 1
Ensure that your compression system is appropriate for its application today
2
Make monitoring the basis of your maintenance programme
3
When things go wrong ensure you (as an organization) address the root causes GET THE BASICS IN PLACE
4
Ensure your ‘inputs’ are clean
5
Give more priority to ensuring your ancillaries are in good condition ALIGN YOUR PEOPLE TO DELIVER
6
Make sure you have one person you can point to who owns the ‘compressor system ‘ and has all the levers to improve it
7
Ensure your organization has a culture of prioritisation and getting the basics right
8
Don’t overlook efficiency
A. UNDERSTAND THE ISSUES 1. Ensure that your compression system is appropriate for its application today Many compressors are used in applications that are no longer appropriate for the design. This can cause them to be unreliable and/ or inefficient. When compressors are specified, they are selected for certain operating conditions, but those conditions inevitably change over time. It is easy to forget the original design requirements, particularly if the equipment is old, personnel leave, or the operating organisation changes. Consequently, as conditions change, companies can end up using the compressor in conditions that are inappropriate. Even one of the best practice compressor operators told us that all their compressors are operating outside their original specifications (but at least they knew this and had taken appropriate mitigations). To establish if this is the case it is worth reviewing the compressor design and asking: • What was the basis of my initial compressor design? • What conditions is the system having to deal with today? • What are the implications of this difference and should changes be made? • What are the options for managing the consequences? The following subsections describe three different ways in which the compression system may have become inappropriate for its application.
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i. Molecular Mass and flow rate
lin e nn in g Ru
lin e Su rg e
Compressor pressure ration PT3/PT2
Compression systems are specified for certain gas conditions, flow rates and delivery pressures. The centrifugal compressor surge control system is based on a ‘map’ for the compressor design and gas conditions. As producing assets age, parameters such as molecular mass and flow rate can change such that the compressor is no longer operating within its ideal zone. Furthermore, as the driver is also specified to provide sufficient power for the design case, if conditions change the power demand can also change. The diagram below shows a typical centrifugal compressor surge map.
Unstable area Surge point 100% 90%
80%
Constant RPM lines
70%
Corrected airflow
Clearly, each compression system has a degree of tolerance and the consequences of changes to conditions may depend on the way the compressor control logic works. However, changes to gas conditions can cause changes to compressor performance. For example, for the same feed condition, compression ratio and compressor speed: 1. as the gas density decreases, the flow rate will decrease, so the compressor will eventually approach a surge condition; 2. or as the gas density increases, the flow rate will increase, which will result in more power consumption. As an example, one user of 30-year-old compressors is experiencing significant decreases in molecular weight which caused a risk of surge and excessive recycle. Options actively being considered are physical changes to the compressor (e.g., re-wheeling) and changes to the control logic. In another example, the electric motor driving a compressor suffered excessive trips. This was caused by increases in the power consumption as a result of increased molecular mass. The user was able to make changes to the molecular mass of the gas by changing the way they operated upstream equipment.
ii. Contaminants or corrosive materials Obviously contaminants or corrosive materials in the process gas can have an effect on the compressor internals. Examples include liquids and particles which can cause deposits leading to vibration and which may need to be removed by appropriate coalescers or strainers, or higher levels of corrosive materials such as H2S or wet CO2, which can cause damage of compressor internals and may require internals made of appropriate materials to be substituted.
iii. Transients This is another area where the compressor may not be able to cope with the demands of the system. In another company, a fuel gas (screw) compressor tripped because it was not able to respond to fluctuations in system pressure sufficiently quickly. Changes elsewhere in the system had caused transients to be greater and more common. A number of possible solutions were proposed including loop tuning, linking of control systems and physical changes to upstream equipment to limit load swings.
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2. Make monitoring the basis of your maintenance programme Some maintenance programmes cause equipment to fail because they are too invasive. Some are excessively conservative and waste money. In most cases, insufficient use is made of condition based measurements (some of which are being generated anyway), as the basis of the maintenance programme for the compression system. The basis for many maintenance programmes is the manufacturer’s recommendations. These tend to be conservative, in part because the manufacturer does not know the context, so has to err on the side of caution. Some operators even suggest that manufacturers have an interest in overly conservative replacement of parts because it enables them to sell more parts and make more money. In addition, when failures occur there is often the belief that the way to improve reliability is to add maintenance. In this context, it is useful to consider an analogy with similar safety and reliability concerns – aviation. Research carried out in the aircraft industry over 40 years ago into the relationship between equipment age and the likelihood of equipment failure for a large number of components, showed that maintenance – particularly invasive maintenance – is not always a force for good. The chart below shows the relationship between the conditional probability of failure (y-axis) and equipment age (x-axis) for a large number of aircraft components. Six distinct patterns were identified (the percentages are the proportions of components that conformed to each of the patterns and the titles are names given to each of the patterns). The research showed that 14% of components failed at random: there was no change in the probability of failure with age, which means that scheduled replacement would do nothing for reliability. It also showed that 68% of components were less reliable when they were new or had been overhauled: hence, scheduled replacement of these components would actually decrease reliability. While the percentages for other industries may vary, the principle is the same – that excessive interference can cause failures.
Bathtub: 4%
A Life: 2%
B Increasing: 5%
C Honeymoon: 7% Warning that it is failing
D Random: 14%
E Infant: 68%
F
Failure
This caused a dramatic rethink in the way the aircraft industry approached maintenance and one of the outcomes was a much greater reliance on predictive / condition-based techniques. Such techniques include performance monitoring and condition monitoring such as vibration, temperature and oil monitoring, the objectives of which are to determine if there are ‘potential failures’ or warnings that something is failing. This enables action to be taken to avoid or minimize the consequences of failure. The advantage of such an approach is that, if the equipment is working well, it is not interfered with, and maintenance is only carried out where necessary - massively reducing the risk of maintenance-induced failures. On modern aircraft a whole range of parameters are monitored, including engine temperatures and pressures, bearing temperature and vibration, and oil condition. Many measurements are continuous and automatic and the information analyzed in real time – often being sent back to a central control room via satellite. This approach has yielded a spectacular improvement in reliability: the rate of fatal accidents due to equipment failure on modern aircraft is 1/1200th what it was in the late 1950s Modern maintenance practices for assets in other industries follow a similar approach to the airlines. Many operating parameters are available through the Distributed Control System and these can be supplemented by additional condition based measurements. For us in oil and gas, a number of compression system maintenance activities, many of which are condition based, are suggested below:
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• Monitoring compressor and driver bearing vibration and temperature
• Monitoring cooling fan bearing vibration and temperature • Checking operation of instruments and protective devices
• Monitoring separator levels
• Checking differential pressures on gas and oil filters
• Monitoring Dry Gas Seal leakage rates
• Cleaning and inspecting separator/ knock out vessel internals
• Checking lube oil and process gas temperature before and after coolers
• Cleaning fans and heat exchangers • Monitoring system delivery pressure and output
• Checking lube oil condition
• Boroscoping of the GT
• Monitoring fuel gas quality
The way to ensure that the maintenance programme does not cause failures and is appropriate for the compressor in its application is to carry out a maintenance review, selecting the best maintenance technique for each likely failure mode. One operator in the Middle East did just this. They were using compressors dating back to the 1960s (not a bad thing in itself ) and a maintenance programme dating back to the same time (which certainly was a bad thing). Regular interventions involved dismantling the reciprocating compressors – to take measurements and replace components – and rebuilding them, an approach that data analysis showed caused more failures than it prevented. By looking at the likely failure modes and selecting the best maintenance techniques for each (these were mainly condition based and ranged from the use of the human senses to vibration and rod-drop monitoring), the maintenance programme was revised, the invasive interventions were eliminated and compressor reliability and maintenance costs improved significantly. An approach that allows monitoring to be at the heart of the compression system maintenance programme is the concept of the Decision Support Centre (DSC). Compressor performance parameters are brought together in a single location to allow specialists to monitor, proactively diagnose and address compressor issues. This information includes process data, work order management, SCADA, production reporting and management of change systems. Sometimes DSCs have additional software such as SmartSignal which is web-based, real-time pattern recognition application which provides continuous monitoring and reports on exceptions for abnormal compressor performance. This allows early identification of abnormal equipment behaviour for proactive problem diagnosis and more effective and efficient prioritization of maintenance activities. As the chart shows below, current practices around DSCs in the North Sea vary considerably, with a third of companies having no centralized monitoring.
Approach to monitoring compressor data in the North Sea 35%
25%
15%
15%
10%
No centralised monitoring
Integrated in local onshore Production Monitoring Centre
Through local Decision Centre for equipment monitoring
Through a Subcontracted Corporate to a rotating Monitoring machinery Centre for specialist rotating machinery (OEM…)
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3. When things go wrong ensure you (as an organization) address the root causes When equipment fails many organizations do not manage to address the root causes of the failures, even when they intend to. As mentioned above, it is common, when equipment fails, for symptoms manifested in one place to have root causes that are failures elsewhere. This is particularly the case with compressors. Clearly, to solve intractable problems, it is necessary to deal with causes of failure rather than their effects. However, when there is pressure to resume production quickly, the immediate concern can be to deal with symptoms and get the equipment running again. If the organisation is stretched, things may often stop there, because there will be other urgent issues to manage. The root cause often remains unaddressed. So, the problem will reoccur. As well as not addressing the root causes, many organisations do not put short term mitigations in place to prevent further deterioration of the equipment while it is out of service for an undetermined period (for example, allowing preservation lube oil systems to run while equipment out of service, and barring over motors/turbines to prevent rotor sag/bending). Most organizations recognise the need to address root causes but very few truly walk the walk. Sometimes the structure is not in place to capture root cause issues and implement the solutions. In some cases people do not dig deep enough and ask ‘why?’ a sufficient number of times (sometimes this can be the famous five, sometimes less, often more). Some examples of compressor root causes, where it was necessary to dig deep and ask why many times include the following:
Keep asking “why” until you find the root causes DIFFERENT ROOT CAUSES FOR THE SAME LOSS EVENT
COMPRESSOR TRIPS
– EVENT –
WHY?
WHY?
WHY?
WHY?
– ROOT CAUSES –
due to vibration
due to liquid carryover
due to inadequate maintenance on separator internals
due to vibration
due to liquid carryover
due to no liquid level in separators
due to vibration
due to liquid carryover in separators
because operators leave the drain valve open
because there is no level control info in the control room & local control is dirty
due to vibration
due to no liquid level in separators
because operators leave the drain valve open
because the level control valve is an on/off design rather than a proportional device
due to GT driver trip
due to failed fuel gas regulating valve
due to particles in the fuel gas
due to lack of ownership because operators leave the drain valve open
due to corrosion caused by high levels of H2S
because the level control loop does not work
because of failures in the sweetening plant
To determine the root causes it is necessary for people to approach problems with a challenging and inquisitive mindset and ask why? It is also necessary to understand the detail of failures. In many cases, failures are caused by small problems that are ‘hidden away’. Data quality is often poor because the people who deal with failures do not have the time to record the detail, the system may not support it, and they never see data being used so there is little incentive to collect it. As a result, root causes are rarely recorded, and the information available is often patchy, inconsistent and vague. Consequently the best information about what the problems are often resides in people’s heads. Oftentimes, experts with responsibility for equipment improvement rely too much on data (often badly collected) and do not draw on this valuable information that resides in their colleague’s heads. The way to improve matters is to provide the systems and structure to allow quality data to be captured well and persuade those who capture the data of the importance of getting it – by showing how it is used to improve performance and ultimately to make their lives easier. It is also important not to rely solely on data – to talk to the people who know the asset best because they work with it every day, and to understand the details of their problems. If the particular details of problems are understood, it will be much easier to deal with the root causes.
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B. GET THE BASICS IN PLACE 4. Ensure your “inputs” are clean Many people feed rubbish into expensive, high precision machines, but are then surprised when the machines fail. The more expensive, sophisticated and important the core equipment, the more one might feel it needs to be ‘looked after’, and target maintenance resources at it. However, as highlighted above, the best approach for such machines is often to leave them alone (while monitoring performance and various parameters) but to concentrate on the quality of what goes into them including lube oil, fuel gas, instrument air, process gas, seal gas and combustion air. Let’s take the analogy of a modern car engine: during manufacture the parts are precisely assembled in a clean environment; hence, most people would quite sensibly choose not to interfere with them, but simply to make sure the air and oil are clean and that the machine is operated sensibly. It is appropriate to apply the same strategy to compressors and to place more emphasis on the equipment providing the inputs. The latter may not be regarded as critical and may not be given sufficient priority in design or maintenance. The solution is for operators, maintainers and maintenance management systems to focus much more on to items such as fuel gas filters, lube oil filters, separator level control valves, level control instruments, instrument air driers, seal gas system valves etc., to ensure that the inputs to the compressor are kept clean. For one user, the biggest single cause of compressor trips was poor quality fuel gas. The gas was received from a sweetening plant, but this was not working properly and did not remove H2S, moisture and particles sufficiently. The operator set up a programme to upgrade the sweetening plant, and ensure it was maintained correctly in the future – in order to improve the reliability of the compressors. The company also had a problem with trips caused by instrument damage resulting from poor quality Instrument Air and initiated a programme to improve its cleanliness through design changes and better maintenance.
5. Give more priority to ensuring your ancillaries are in good condition Ancillary equipment that is crucial for reliable compressor operations is often neglected. Yet in a survey of two companies, we found that more than a third of compressor losses were caused by ancillaries:
More than a third of compressor trips are recorded as ancillary failures PROPORTIONS OF ANCILLARY & COMPONENT FAILURE % of root causes for the “unplanned loss” benchmarked operators
36% Other issues
Ancillary failure
38%
26% Component failure
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Equipment like fans, coolers, separators (and their associated level control systems), fuel gas conditioning and regulating equipment, lube oil pumps and filters, GT air inlet systems, seal gas filters and valves are often seen as not ‘core’ to the process. This is reinforced by the fact that many are (relatively) inexpensive, so they are not always given the attention and the maintenance priority they deserve. Designers under pressure to reduce costs might see such equipment as good opportunities to save money, and operators and maintainers may believe they have more important priorities. Consequently it is not uncommon to see such equipment in a poor condition, or even left in a failed state. However, these ancillaries are crucial for the long term condition and smooth running of the compressor. One user suffered from compressor trips due to vibration, and noticed solid deposits on the impellers which were probably caused by liquid carryover. The vibration trips were eliminated by retrofitting new, high efficiency internals to selected slug catchers and separators and upgrading unreliable level control instruments. One (but certainly not the only) reason some important ancillary equipment is sometimes not maintained is that nobody sees it as their responsibility, since some equipment and some functions can ‘fall through the cracks’. For example, slug catchers and separators are usually regarded as static devices, and in many organizations, the responsibility for their maintenance rests with the static/integrity department. However, the integrity department is often quite small and is fully occupied managing integrity and hydrocarbon containment due to corrosion, erosion etc, on a whole range of ageing assets. Even if the question of the condition of slug catcher and separator internals has occurred to them, it will not feature very high on their list of priorities. One operator had problems with centrifugal compressor vibration trips due to liquid carryover and had not looked at slug catcher and separator internals for 30 years. When they did inspect the internals there was nothing left! Another example of equipment that can ‘fall through the cracks’ is valves. In many organizations the instrument department is responsible for valves, since valves are often associated with the loops and instruments the department looks after. However, what about large valves? Are these covered by the Instrument department too? And, if they are, do the personnel in this department have the experience/ interest in the maintenance of items of equipment that are so different to the equipment they normally work with? It is important to look out for equipment and functions that can get overlooked and ensure maintenance responsibilities are defined and understood, and that appropriate competencies are in place.
C. ALIGN YOUR PEOPLE TO DELIVER 6. Make sure you have one person you can point to who owns the “compressor system” and has all the levers to improve it Some rotating equipment specialists do not have the levers to improve performance of the equipment they are responsible for. There are various reasons why this may be the case. Many organizations do not have a large number of rotating equipment specialists, so rather than distribute them amongst the assets, they often tend to be embedded in a function. This means that they do not have direct authority in the organizational structure, so have to influence through persuasion. These are difficult problems to fix. Rotating equipment specialists do not grow on trees and it is difficult to make people accountable for performance on assets, operated and maintained by colleagues they do not know and have no line authority over. However, it is important to have one person, such as a rotating equipment specialist, you can point to who owns the “compressor system” and can control the levers to improve it. This is where the concept of a Decision Support Centre (DSC) comes in again. The DCS provides an environment for collaborating and sharing learnings across locations. This is enabled by video-sharing and a single, shared view of the Compression Process. By bringing together all relevant information about critical equipment (particularly continuous monitoring parameters discussed above), the equipment specialist can analyse data more quickly and more accurately, reach appropriate conclusions in good time, and coordinate action at site. Within the Compression DSC, the Compression DSC Specialist can: • monitor processes across fields and assets • share a common view of data, trends, models, analyses, results and decisions • collaborate with multiple field and local and remote experts to help solve problems • work through issues and develop solutions
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An important aspect of the DCS is that it facilitates cross-functional collaboration and decision making – by providing a common, shared, objective view of the equipment. It brings expertise of rotating equipment specialists directly to bear on the problem and enables you to hold him/ her accountable for driving solutions. Another area where appropriate ownership is needed is the management of spares. Equipment downtime is often longer than it needs to be because the correct spares are not available. One reason this can happen is that equipment sitting in stores and not being used is viewed in some parts of the organization as an expense rather than an insurance policy. Finance people often exert pressure to reduce inventory because it is seen as money tied up. Since the stores operation costs money to run there is the understandable pressure to control costs from this source also. In some organisations spares decisions are not taken by people with responsibility for the availability of the asset. In one organisation this even led to a decision to dispose of all equipment in stores that had not moved for a specified number of years. Unfortunately in many cases, the spares that are used less are often the most critical and the longest to procure, so adopting a one-sided view can turn out to be extremely costly and short sighted. To make sure appropriate spares are held it is important to carry out a review which considers the demand rate, the lead time to procure and the consequences if the spare is required but not available. Such a review should involve the people who have operational responsibilities (the rotating equipment specialists plus operators). The review can include alternative or intermediate options like stocking semi-finished components, vendor stocking and sharing between assets or companies. One suggestion to minimize downtime for critical equipment is for operators to have “Spares Kit Boxes”.
7. Ensure your organization has a culture of prioritization and getting the basics right Some organizations fail to carry out the basics of asset management properly. A common and hopefully reassuring theme from many of the best practices above is the importance of basic maintenance and housekeeping. Keeping ancillary equipment in good condition is not rocket science, yet these things are often not done correctly. Many failures occur because of issues like poor oil management, failure to check gauges and readings such as differential pressures across filters and act upon them, failure to fix failed instruments and valves, lack of appropriate spares (sometimes even simple things like o-rings), failure to spot a small leak before it becomes a large leak, failure to check levels, or to clean local level indicating instruments etc. A major cause of failures that “should not happen” is, of course, people. In principle, understanding how to operate and maintain equipment, writing appropriate procedures, ensuring sufficient people of the right competence are available to do the necessary work, and carrying out the work correctly, is relatively straightforward. However, a high proportion of failures are due to factors such as lack of training and/or lack of operational discipline. Ensuring people are fully competent for their jobs and keeping their skills up-to-date is critical for reliability. Regular, well-structured “on-the-job training” can be an extremely effective way to do this, yet in a poll of North Sea operators less than 50% undertake this. Another cause of failures is the acceptance of imperfection: having to live with, and tolerate an environment that is not optimal. This situation is inevitable in older, declining assets where costs need to be controlled. However, because some imperfections must be tolerated, there is often the temptation to tolerate all imperfections. The culture of imperfection becomes ingrained and self-fulfilling. Cultural issues are difficult to turn around. To do so requires leadership and commitment – to identify priorities and ensure that improvement efforts are driven through. Organisations need to ensure that a system is in place for managing the basics, that operators and maintainers understand what the priorities are, that they are alert to problems with the system and equipment, that they raise any problems they find, and that the problems are acted upon. Getting the basics right extends not only to operating equipment well but also to managing the problems that inevitably occur. Initiatives often (quite rightly) focus on reducing the frequency of unplanned events. However, it is sometimes overlooked that losses can also be minimized by reducing the duration of shutdowns, including the duration of planned maintenance outages. Indeed very few companies measure their response times to events (how long in identifying the issue?, how long in sourcing parts?, how long in fixing?, how long in ramping up?). Outages can only be successful when the work is planned effectively before it is scheduled and/or started. Effective planning should address areas such as the control of the outage scope, definition of tasks, determination of materials, tools and equipment requirements, estimation of labour requirements and work group coordination. Again this applies to all losses, extending beyond compressors. But if we could improve turnaround times for unplanned compressor losses by 50%, we could increase industry revenues by over $1bn.
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8. Don’t overlook efficiency Sometimes compression system efficiency is overlooked and money is wasted as a result. By lost efficiency we mean a situation in which the equipment is still “working” but its output is reduced, or its inputs are greater. The reason this happens is that people are (rightly) concerned with total failure, so that partial failure can be overlooked. In addition, a common problem with lost efficiency is that it is unnoticed because many relevant parameters are not measured. Relatively small efficiency losses that are allowed to continue for weeks and months can then become significant. One user with a fleet of 10 compressors was concerned about reliability, because the demand on the compressors was close to their capacity. An efficiency related failure mode was labyrinth seal wear which affected compressor output relatively quickly and significantly. Because the compressors were still ‘working’ the importance of efficiency losses to the system were not given sufficient attention. It did not seem to have been appreciated that a 10% efficiency loss over 1 year, had a similar effect as a single compressor being down for just over a month. Other failure modes that can affect efficiency are recycle valve leakage, constant recycle and the GT inlet air filter being clogged. The way to deal with this is proactively to consider efficiency losses and design appropriate measures and actions.
Section 3: A structured way to investigate compressor issues A structured series of questions can be used to understand the compression system and why it is failing.
1
2
What is it?
3 What is its purpose?
4 What has changed?
5 Who is responsible?
6 How is failure data recorded?
7 What are the main symptoms?
What are the causes of these symptoms?
The questions below are suggested examples and relate to each of these steps:
1. What type of compressor is used? What is it driven by? What other elements are in the compression system?
5. How are failures recorded? What is the quality of the data? Are there any KPIs (e.g., MTBF)? How are they measured?
2. What is the compression system used for? Where does the gas come from? Where does it go to?
6. What are the biggest problems with the compressor system? How are these manifested? What are the main concerns looking forward?
3. How old is the system? Have there been any changes to the equipment? Have there been any changes to the gas?
4. Who operates the compressor and maintains it? To what extent is the manufacturer involved? Are any specialists available?
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7. What are the root causes of the problems? What actions should be taken to deal with them? Who should be responsible for dealing with them?
Unplanned losses working group contact details
Jim Gordon TAQA Operations Support Manager jim.gordon@taqaglobal.com
Steve Gardyne Talisman-Sinopec Energy Head of Production Engineering and Operations Services sgardyne@talisman-sinopec.com
Paul Jamieson Chevron UK Operations Manager jamiep@chevron.com
Chris James Schlumberger Business Consulting Reliability/ Compressors Expert CJames@slb.com
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