One of the biggest applications for gaskets is sealing joints between pipes and devices like pumps and valves. Welding isn’t an option as it may be necessary to take the unit out of service at some point. Instead, each side of the joint has a flange and they’re bolted together with a gasket in between.
Whenever a flanged joint is opened up it’s important to install a new gasket. Obviously, this has to be the right size and to minimize downtime you need the gasket at hand before taking the joint apart. So how do you determine what size is needed? Well, the answer is, use the ASME standards.
Know the Flange Standards
Two main standards define pipe flanges: ASME B16.5 and B16.47. B16.5 covers flanges used on pipes from 1/2” NPS to 24” NPS. B16.47 addresses pipes from 26” to 60” NPS.
NPS (Nominal Pipe Size) refers to bore diameter. That makes it difficult to determine what size you’re dealing with. If you put calipers on the OD you also need to know the wall thickness. Alternatively, measure the outside diameter of the flange and refer to the appropriate standard.
Two other standards used to define pipes and flanges are MSS SP-44 and API 605. Fortunately, both are also part of ASME B16.47. Flanges complying with MSS SP-44 are defined as Series A while those meeting API 605 are Series B. The Series A flanges are intended for higher clamping loads, so are thicker and have a larger bolt circle diameter.
Standards for Flange Gaskets
Sensibly, ASME has two gasket standards that are closely related to those for flanges. These are B16.21: Nonmetallic Flat Gaskets for Pipe Flanges, and B16.20: Metallic Gaskets for Pipe Flanges.
Ask The Experts
If you don’t have a copy of B16.5, B16.47, B16.20 or B16.21 to hand, don’t guess at what gasket you need. You can look it up online, but it’s easier to call us with the details. One of our gasket material specialists will discuss your application with you and help figure out what size and material you need.