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Starflex Sealing India Pvt. Ltd.
 

About Starflex Sealing(formerly Flexitallic) India Pvt. Ltd
Starflex presented a paper on "Productivity and other losses resulting from gasket problems" at National Seminar on Innovative Strategies in Process Plant Efficiency Improvement (ISPPEI-2003)held on February 22nd, 2003 by Applied Chemistry Alumni Association (ACAA) of Calcutta University, Mumbai Chapter. Following are its contents:

Productivity and other losses resulting from gasket problems

Those in manufacturing sector, especially in chemical industry are well aware what a poor quality or wrong installation of gasket can do to plant uptime. An improperly designed, casually installed, poor quality gasket can lead to plants shutdowns, large sums of financial losses, reduction in plant capacities and above all cause considerable environmental damage and pose safety hazards, which are sometimes fatal.Some of the points, which need our attention to improve this situation, are discussed bellow.

Attention to Gaskets during plant turnarounds

One would find that during a plant turnaround, in most cases gasket is the only product replaced in a piping system or in the static equipment being inspected. While a lot of attention is paid to the equipment inspection but often the attention the gaskets need is missing. From engineering personnel to operating staff, everyone is concerned about how fast equipment can be brought back to service and in the process of urgency, missing a few of the known elements of boxing up flanges. It may be mentioned that the system is only as strong as its weakest link, which in many cases is the gasket!
In most of the organizations standard inspection procedures do not call for gaskets and flanges inspection. Focus remains primarily on equipment being inspected leaving a large no of bolted joints un-inspected. This lack of attention leads to a situation where integrity of flange joint, practically speaking, is in the hands of maintenance contractor. Employment of lowest bid contractors may end up in just one leaky joint to significantly affect the performance of a team.
A single flange leak delays the testing of the whole piping loop. There may be a few gaskets like channel to shell gaskets of heat exchangers, which will be very costly to replace in terms of delay they cause if, found leaking after box-up. While it is practically difficult to pay equal attention to all joints, it is worth identifying at least vital joints at the planning stage.
Understanding gasket specifications

Though the standards specify required quality testing parameters, there are barely a few who make an effort to ensure that gaskets conform to standards. Gaskets, considered as consumables, are sometimes ordered in bulk without adequate attention to quality.

The gaskets, bolts, and flanges are designed such that they can maintain a higher stress than the internal pressure and hydrostatic end force in order to maintain a seal. The gasket also needs to maintain recovery in thickness characteristics to maintain the required stress during un-torqueing of bolts and flange due to temperature and pressure fluctuations.The temperature and pressure resistance properties with respect to the application also need to be ascertained during designA leakage would occur as a result of mishandling or if any of the above are out of line.Some of the important quality parameters of gaskets are:
  1. Density

    All gaskets should consistently exhibit compression recovery at the defined stress in order to maintain a seal.The bolts, and flanges are designed keeping this in mind. Imagine, in one instance, a gasket whichis supposed to compress 25% compresses 40% at the specified stress.During the next use, the same specifications gasket from the same source compresses 14% at the same specified torque.

    The gasket that compressed 40% instead of 25% would lead us having a load lower than the minimum required load for operating condition as well as gasket seating.This gasket would not have the properties to maintain the stress levels for a long duration and would lead to premature leakage.If it is a spiral wound gasket, excessive compression stress would put strain on the outer ring which is harder and would damage the surface of the flange.

    Conversely, the gasket that compressed 14% instead of 25% would lead us to a require a higher load than the design load to achieve the require compression.The flange and bolts are not designed taking this excessive load into consideration.Although there would be no immediate effects, there would be a slow permanent damage to the equipment, which would lead to problems such as bending of the flange, stretching of the bolts, and distortions on the flange surface.This would also lead to reduced ability of the equipment to maintain high levels of stresses which would force reduction in operating pressure within the system to maintain a seal, and thus may lead to reduced production levels.

  2. Raw Material Quality

    Raw material quality is another important factor that can influence sealing performance.All materials are rated to withstand a particular temperature and pressure on the assumption that they are supplied in conformance to the required technical parameters.For example, following are typical properties for graphite.

    PROPERTIES  
    Purity 98%
    Density

    1.0g/cm3
    Leachable Chloride ion 50 ppm
    Leachable Fluoride ion content 50 ppm
    Ash Content 2%
    Temp.Range in oxidizing atm. 450 C

    Unfortunately, the demand for lowest prices leads to compromise on quality of graphite. A compromise in purity levels, or leachable chloride/ fluoride contents changes the performance characteristics of the material. Such material would oxidize at lower temperatures of even 300 C. Additionally, higher chloride/ fluoride content can also contaminate the system specially in critical applications such as nuclear power plants.

    Similarly, there are problems with other gasket raw materials that can lead to problems. For example if the gasket is supposed to oil resistance but actually absorbs oil above acceptable limits and changes in dimensions, one will end up having repeated leaks.

    There are numerous applications that suffer huge production losses due to constant gasket leakages. In a lot of such cases, the problem is a result of cheap gasket selection.
 
Innovative products

There are a lot of innovative products that can enhance sealing performance and reduce such problems. PTFE for example suffers extensively from creep and cold flow. It leads to leakage the moment the flange and bolts loosen. Unfortunately, PTFE is the best option for acid resistance and can not be replaced. There are numerous applications where the plant is forced to shut monthly due to leakage in PTFE gaskets. The production losses in such cases are huge. Fortunately, there are special PTFE products which offer very good resistance to creep and cold flow, and maintain superior stress retention. Although such products are more expensive, they help improve production through reduced shutdowns, and thus have replaced all gaskets in such applications in the West. There are innovative products like cammprofile gaskets, Low stress gaskets, weld gaskets, flexicarb sheeting materials etc, awareness of which can definitely help the industry to solve critical gasket applications. There are products available to take care of gasket leaks due to gasket porosity, gasket creep and evenvibrations and hammering in pipelines.

Conclusion
  

As we all know in practice, it is very difficult to train all engineering staff on gasket selection and quality standards and even more to the workmen who handle them. The best ways to reduce the ‘Leaks’ menace are:
  1. Understand and spread the knowledge and importance of gaskets.

  2. Have flanges inspection and gasket installation checks as part of turn around inspection procedures [at least identify and inspect the joints which shall call for longer shutdowns/ are the most unsafe joints when leaking].

    3.
  3. Purchase gaskets with a stricter quality standard from a manufacturer who can demonstrate conformance to specifications.

    4.
  4. Try innovative products for problem sealing cases.
(A properly selected ‘Quality’ gasket shall definitely payoff in long run.)
 
   
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