Is there a difference between the two

[wenc72]

I'm reviewing a fabrication drawing and it is calling for 2"-3000# couplings and 4" API couplings. I was wondering why the 4" is not called out as a 3000# designation? Is there a difference between the two and if so what?

 

[LittleInch]

I'm pretty sure 3000 psi fittings only go to 2", though bonney forge seem to imply they can go to 4", it's not commonly used AFAIK

http://www.bonneyforge.com/resources/FSFU.pdf

I've no real idea what an "API coupling" is. This is rather vague (at least to me).

API what?
Pressure rating?
Type?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

Check the API-5L standard for the 4" coupling detail which may fit the service condition you have.
The different pressure rating for 2" and 4" fitting may come from the different standards, such as ANSI vs API.