Maintenance
Bol te d j oi n t in teg r ity s e r v ices
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Industrial Sectors - Steelworks - Food - Thermoelectric power plants - Paper Factory - Chemicals and Petrochemicals Plants - Refineries
Flanged joints Type N OT E S O N F LA N G E D J O I N T S
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n production, processing, storage and transport systems of fluids there are boted flange joints with ring type gaskets, which connect equipment, lines, tanks or assemblies together. The flanged joint, compared to a welded joint, offers obvious
advantages in the prefabrication phase of components or plant sections; moreover, the inspections are easier, the maintenance and replacement of faster components. However, each flanged joint is a potential source of danger if it not maintained with method and competence. Too many accidents and near misses occur every year due to leaks from flanged joints; causes could be, for example, an insufficient specific knowledge of the maintenance activities, the underestimation of the risks in case of leakage and an inadequate application of the operating instructions .
References
A flanged joint can be like a welded joint. As for fixed joints, even for flanged connections it is essential that operators are specialized, trained, that suitable equipment is used and that there are specific installation procedures, so that the Essential Safety Requirements are met. As well as a welding that is not carried out correctly, even a wrong assembly of a flange could cause damage, even considerable, to things, people and the environment.
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Tightening Methods T I G H T E N I N G TO RQ U E By using manual, pneumatic or hydraulic torque wrenches, it is possible to tighten flanged joints with bolts of any diameter. The use of the hydraulic dynamometric wrench represents a simple and reliable solution for the tightening of flanged couplings; the tightening torque control allows, in fact, to supply the bolts with the required load with a good approximation (± 10%). Depending on the model chosen, keys develop a torque between 200 Nm, ideal for providing a “correct” stress to the bolts in the case, for example, it is important not to exceed certain load values on the seal, up to 35000 Nm, sufficient value to supply a tension of 300 N / mm2 to 4” bolts.
B O LT T E N S I O N I N G
U LT R A S O N I C B O LT M E A S U R E M E N T
Available in a wide range of models for bolts up to 6 “they are able to develop a
Load measurement through an ultrasonic
maximum load of 5,000 kN.
system, associated with both tightening with a
The tensioner consists of an annular piston interposed between a threaded insert,
torque wrench and direct tensioning, serves to
screwed to the end of the bolts, and a support bridge, provided with a slot on the
verify that the residual tension on the tie rod
base to allow access to the nut with a special pin (tommy bar).
corresponds to the theoretical value required.
The load applied directly to the bolt extends it, making it possible to rotate the nut by hand by means of a bar to be inserted in the holes made on the nut’s faces,
This measurement is generally carried out
or, should it be lacking, on the holes of the outer crown of a special hexagonal
using an ultrasound system, whose operating
bush.
principle is based on measuring the time taken
For the application of hydraulic tensioners, it is necessary that each bolt protrudes
by a shock wave to cover the entire length of
from the nut of an equal length at least once its diameter.
the bolt; from this measurement, carried out
It is advisable to tighten at least on 4 bolts at the same time, to compress the
before and after tensioning, we go back to the
gasket uniformly, avoiding load asymmetries and consequent stress phenomena.
lengthening suffered by the bolt and therefore
The method is extremely precise (± 5%) because it is independent of friction and
to the tension applied on it.
torsional stresses found in traditional torque tightening systems.
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Full Bolting Service Multiple benefits from FBS application FBS program (Full Bolting Service) aims to improve the reliability of flanged bolted joints with gaskets, whether they are of line, equipment or instrumentation, to make them efficient and reliable and not to give rise to leaks in any operating condition and due to any type of thermomechanical stress from type of plant where they are in.
WHY FBS It is common to find joints in system that leave leakages produced from the inside outwards, due to the high pressure to which the joint is subjected (leakage). The product that comes out could be dangerous for both environment and health, and sometimes give rise to situations of high risk with catastrophic consequences. The reasons why through a joint there is product leakage can be multiple and almost always referable to a wrong maintenance, consequence of an approach that does not identify and appropriately evaluates the elements that have greater influence in achieving the final objective, “the seal to the pressure “. Therefore, it is considered necessary to implement a maintenance program that minimizes the leaks from the flanged joints.
W H Y A F LA N G E B O LT E D J O I N T I S A F F E C T E D B Y L E A K A G E ? The leak through a joint occurs if during any operating conditions, the residual load on the gasket is such that on the whole development of it, is not less than the minimum required, depending on the pressure, the gasket and the finish of the contact surfaces of the flanges. If this condition does not occur in a portion, even a small one, there is the beginning of the leakage which could undergo changes in flow, usually increasing, sometimes it could even disappear and then reappear and sometimes disappear completely (thermomechanical actions). Briefly we will say that to maintain the internal pressure it is enough that the residual load on the gasket is never less than the minimum necessary.
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Full Bolting Service Multiple benefits from FBS application Of some joints that have historically shown leaks despite having already been treated with special care previously, a careful and accurate analysis will be performed, and they will be redesigned, with the study of the gasket installed and if it is deemed necessary to replace it with another technologically more powerful. It may be considered necessary to make observations on the disassembled joint and gasket, all elements that will increase the information and quality of them to be able to produce an intervention project which will lead to the achievement of the best result. A redesign intervention can concern one or more of the following elements: • Changing bolts an nuts material; • Installation of washers under the nuts; • Change of seal gasket seat finish; • Changing the type of gasket or the simple geometry of the one fitted; • Changing the flange face; • Remove damage caused by nuts embedded in the flanges; • Special instructions for joint assembly; • Calculation of tightening loads and application sequence; • Indications for monitoring the joint during operation and checking operations after stops and before restarting o following reductions in operating conditions. The items listed above are the most immediate, but others can be added to them.
PLANT OPERATIONS Our service includes the actual maintenance activity. We have equipment for disassembly, maintenance as described above, and joint assembly. We have operational staff, and a coordination structure for it, specializing in bolting activities with long experience in the field and over the years have been able to deal with situations of all kinds, developing particular skills in the technical and managerial approach of what it is detected in the system, producing solutions within the time required and imposed by the need to respect the programs. Our way of operating in the plant is such as to allow the client to realize that nothing is overlooked, and nothing is left to chance. All the operations planned for the maintenance of the joints are monitored and evidence is given on the lables that are fixed to the joint to allow anyone to verify the actual execution of the activity.
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Applying Washers The excellent help, without side effects
WHAT KIND OF DAMAGES HAVE BEEN RECOGNIZED DURING MAINTENANCE WITH BOLTED FLANGED JOINTS ? It happens that after tightening, the nut rotating against the surface of the flange generates a dimple and, in this case, the linear relationship between the tightening torque and the tension on the bolt is lost. We know that this phenomenon is more marked on small size bolts. As the size of nuts and bolts increases, the phenomenon is less frequent but the use of adequate washers remains a very effective measure. It is proven that the use of hard material washers improves the load transmission on the bolts. The washers preserve the surfaces of the flanges from the friction actions of the rotating nuts, and reduce, even in the case of Bolt tensioning, the relaxation phenomena due to the effects of collection of the nut on the surface of the flanges (local deformation on the flange which increases with the spend time.
V E D WA S H E R S A DVA N TAG E S The specific pressure differences trigger the seizure with between the nut and the surface of the flange with consequent tearing of the material. The use of washers of adequate thickness and external diameter will reduce the specific pressure on the flange, minimizing the effects of recessing (localized deformation on the flange which increases with the passage of time) particularly in case of high temperatures. VED has designed and manufactured washers with geometric and mechanical features that significantly improve the reliability of flanged joints.
A WASHER AND IMPROVEMENTS ON NUTS TO PREVENT DAMAGES TO BOLTS AND DURING FLANGES MAINTENANCE. Frame the QR-Code to download the complete document issued in collaboration with INAIL and presented to the SAFAP2018.
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ASP&ASG Advantages Sealing solution on air cooler exchangers
VED HAS DESIGNED AND PATENTED SPECIFIC GASKET CAPS AND SPECIFICATIONS During operating conditions of the systems, there may be fluid leaks outside from the inspection holes of air exchangers (air coolers or air fin) on which, often, it is difficult to intervene.
In these cases, containment boxes are built and installed
The image above shows a device on which several containment
directly attached to the caps in which to inject the sealing
lids have been installed to eliminate, with the system running,
compound.
as many leaks from the spy holes.
VED PREVENTIVE ASP & ASG SOLUTION To definitively solve the problem, VED has designed a sealing system consisting of a patented gasket and plug. The VED plug allows, if necessary, the injection of the sealing compound to seal the leak under pressure.
To obtain the best result, the supply of the plug is often associated with a maintenance intervention, which includes the disassembly of existing plugs, the restoration of damaged holes and the installation of special plugs. The name “ASP” is an abbreviation of “Air coolers Special Plug” while “ASG” is an abbreviation of “Air coolers Special Gasket”.
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Conta cts 96010 Melilli (Sr) Zona Ind. Bondifè Tel. 0931 776111 Fax 0931 776136 85059 Viggiano (Pz) Zona Case Rosse Tel. 3429573531 72100 Brindisi c/o Versalis Tel. 0831 546016 Fax 0831 546016 09032 Assemini (Ca) Z.I. Macchiareddu 5° Strada Traversa A Tel. 070 241156 Fax. 070 2548133 31032 Casale sul Sile (Tv) Via M.L. King 58 Tel. 0422 821382 Fax 0422 821283 21055 Gorla Minore (Va) Via A. Colombo 176 Tel. 0331 576780 Fax 0331 465600 Registered Office VED Srl 96010 Priolo (Sr) Via Blanco 2
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