MSS SP-95/NPT Galvanised Air Header

[sangfroid]

I am currently designing an instrument air distribution pipeline (for actuators, control valves etc). Working to a specification, it states "Piping from the isolation valves on the main instrument air supply header to individual consumer shall be of galvanized carbon steel pipe and NPT threaded fittings". The corresponding carbon steel piping specification only mentions a standard "MSS SP-95" AND all valves are to be ASME flanged, not threaded at all. I have never worked with NPT threaded pipe before (only tube compression fittings) and the concept of threaded galvanised *piping* is foreign to me. Could someone explain (a) whether MSS SP-95 and NPT standards are interchangeable; and (b) why would galvanised piping be used?

Thanks in advance, SF.

 

[LittleInch]

Mss sp 95 is a standard for nipples and plugs. NPT is a thread standard (National Pipe Thread Taper), hence different things, not interchangeable.

Galvanised is used for corrosion protection.

See also this thread about a similar thing, which has info on sealant. Search this site for sealing screwed piping and screwed air piping.

http://www.eng-tips.com/viewthread.cfm?qid=352301

You need to have a good design and lots of couplers as you need to work away from any elbow or tee as opposed to trying to screw it into the right orientation. Takes some pre thought as to how to do it efficiently or you'll run out of bits quickly...

Using screwed flanges for valves means they should be in the correct orientation, but is somewhat at odds with a screwed system.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way