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Curing Chronic Pipe Leakage

How the raised surface profile of PTFE sheet gasket helped a midstream oil and gas processor address leaky pipes

Bolted flange-gasket connections in process piping systems are common and given little thought – unless they start to leak.

Chronic leakage proved to be an issue for one of Garlock’s clients, a midstream oil and gas processor and services provider. The site processes, stores, and transports natural gas, liquefied natural gas and petroleum products. Garlock was brought in to provide a solution to the problem.

Successful connections are dependent on a variety of things, including the state of the flange surfaces, alignment, bolt and nut grade and strength, bolt and nut thread condition, lubrication, bolt tightening process, service conditions, and choice of gasket.

When a flange-gasket joint is assembled, the gasket must first be compressed to fill the gaps between the flange surfaces, creating a seal when system pressure is applied. Secondly, it must maintain that seal as the system is brought on-line and temperature and pressure escalate.

As the temperature increases, a gasket made of non-metallic materials such as rubber, fibre, PTFE and inorganic fillers is prone to lose thickness, that is, creep. And the thicker the gasket is, the
more it is prone to creep (1/8-inch thick gaskets creep more than 1/16-inch).

The two most important performance qualities of a gasket are its ability to seal and its ability maintain that seal. These can be indicated by industry standard tests for sealability and creep.

On the surface, this particular case study would seem to be an application of little complexity. However, the details of the joint gave rise to several issues that caused the user chronic leakage problems. Here are the service conditions and background of this particular case:

  • Temperature: 100°F to 120°F (38°C to 49°C)
  • Flanges and use: 18-inch Class 150 raised face flanges used in the pipe systems of cooling tower water pumps. Multiple gaskets are on either side of spool piece
  • Media: Water
  • Pressure: 100 psig to 150 psig (7 bar-g to 10.3 bar-g)

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