Gaskets

1Q. Anything you can tell me about keeping gaskets from leaking?

1A. Keep the bolts tight, use the correct gasket, and do your bolt and gasket calculations.

2Q. What are typical nominal clamping gasket stresses used in industry?

2A. Sheet 5-22 ksi (30-150 MPa), double jacket 15-22 ksi (100-150 MPa), spiral wound 8 to 44 ksi (50-300 MPa) with inner ring, solid metal 30-90 ksi (200-600 Mpa), Camprofile 10-30 ksi (70-200 MPa). Always consult the gasket manufacture for specifics on their gaskets as these are only guidelines and depend on the temperatures. Make sure the bolts don't yield especially at higher temperatures or pressures.

3Q. When the gasket clamping stresses are correct and the bolts are tight and the gasket still leaks what can be the problem?

3A. The gasket or clamping surfaces may be damaged, the incorrect bolt tightening procedure may have been used, the wrong type gasket may have been used and relaxed, the flange may be distorting, meaning wavy or non parallel and will need to be checked for robustness, temperature swings may be affecting the the clamping load (see Hydrocarbon Processing April 2002, Case 8: "Analyzing a leaking heat exchanger gasket"), external loads such as piping loads may be opening the flange, are a few possible causes. As you can see a satisfactory gasketed joint requires a well engineered design and installation.

4Q. What happens to a gasket when it is over compressed?

4A. A jacketed gasket may actually crack its outer jacket if over compressed and their is no stop. By no stop is meant a step which only allows it to compress so far. A spiral wound gasket with an inner or outer ring can only compress to the thickness of the ring when it goes metal to metal, so you can really tighten the bolts. Be careful though, flanges distort and other bad things can happen with over tightening.

5Q. What is the most common cause of heat exchanger head gasket leaks?

5A. While this is a complex subject, my experience has been inadequate gasket stress. Gaskets can lose their "spring back" and compression with cyclic thermal loading. After a year, they may have lost 30% or more of the assembly load. Correct tightening procedures are very important to keep large gaskets from losing too much of their assembly stress or "wrinkling" the gasket.