Slip On Flanges in Steam Service 3

[engineeringguy]

I have a client requesting slip on flanges for a steam application. I have another client who is adamant that this poses a safety concern and will only accept butt or socket type connections in steam service (ANSI 1500).

I've tried to get a full answer to why this is but I cannot get a rational response. The best I can get is that slip on flange connections are not as strong as weld neck or socket type connections. Why?



"If experience was always the only factor, how would we get to the moon?"

http://www.piping-designer.com

 

[KernOily]

Uhh, what does your client's piping specs say for this line class and commodity? Doesn't his spec set forth whether you use a SO or WN for this commodity?

You DO have a spec, right?

If I understand your problem correctly, this is not B31.1 service, therefore 31.1 is not applicable.

A SO flange might be more flexible than a WN, but you'll be hard-put to prove that in your oil patch design without busting out your FEM software. CAESAR will not let you make the distinction between SO and WEN, as far as I know.

Bottom line is that this call belongs to the client, his piping spec, and his insurance carrier. If he has no spec, report back here for next steps...

 

[mizzoueng]

DSB,

I haven't been able to find it. I probably read it somewhere, but don't remember where.

 

[DSB123]

mizzoueng,
If you read that when you find the reference recommend you find the nearest bin and dump it because it is definitely wrong.

 

[HawksHockey]

Someone may have mentioned this previously, but... Weld Neck Flanges give the client the opportunity to perform a radiographic examination on the welded joint, whereas the slip on flange welds can only be tested using a surface indication test like magnetic particle. There is no real method for testing for voids, inclusions or any other type of internal weld defect on the slip on flange welds (fillet welds). Also, the opportunity to cheat on a slip on (or socket) flange exists, and nobody will ever know unless the internal fit is inspected (slip on flange). There is no way to check a socket flange. I would imagine that the "client" does not want to check into every flange weld to ensure that it meets the applicable code, the "client" just wants the material installed with no hassle. With #1500 flanges, I would expect the pressure to be quite high, and I wouldn't want anyone cheating my installation - therefore WN Flanges it is.

 

[StressGuy]

SO flanges are simply evil, pure and simple. Few things give a stress engineer (at least, one who knows anything) more fits than having to deal with a system made with slip on flanges.

2000psi and 500°F? That's definitely not something to be playing around with.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.