higher strength materials for pressure vessels in ASME B31.3

[ktgottfr]

Greetings,
I am designing a small fitting to be installed inline on a 1-1/2" pipe. This fitting is basically a small pressure vessel packed full of components (so that there is very little free internal volume) and is required to be machined out of a solid block of material.
Now, here is my problem. Another engineer has told me that for asme b31.3 or a category H fitting, that there are severe limits on what materials can be used. Apparently only forged billets or plate can be used for pressure holding components, and the maximum allowable stress is 17ksi for any material regardless of actual yeild strength etc.
When I read ASME B31.3 I do not see these limits written anywhere(although they may still be there). It seems to me that I can use any material in table A-1 for my pressure vessel.
Does anyone here have any insight to this problem? It would be helpful to me if I could make my fitting from a higher strength material, but not completely necessary... thanks!
-Kristjan

 

[vpl]

If it's a pressure vessel, than why does B31.3, Process Piping, apply? Shouldn't you be designing to Section VIII of the Boiler and Pressure Vessel Code?? Please look at paragraph 300.1.3 Exclusions.

Patricia Lougheed

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[ktgottfr]

It looks like you are correct. I am looking at the wrong code. I will discuss with the other engineers here and adjust my question accordingly. Thanks!

-Kristjan

 

[btrueblood]

Erm. If it's a component of a piping system, i.e. is not intended to hold a significant volume of fluid, it is not covered by the BPV, and you default to the piping code. Which...when you grind down to the end of the calc's. for non-standard piping components, pretty much refer you back to the BPV code anyway...

 

[Canadieng]

Kristjan

Where abouts are you located? For this application it would be most appropriate to talk directly with your jurisdiction/AI.

For example, here are some newsletter discussions

Ontario:

http://www.deltathx.com/uploadsDocs/Understanding heat exchangers.pdf

Alberta (page 4):

http://www.absa.ca/newsletter/2008-v13-iss2.pdf

 

[Canadieng]

Also see, for Ontario:

http://www.tssa.org/CorpLibrary/ArticleFile.asp?Instance=136&ID=E121CECFBC82487D86D12B0EC41F9820

 

[ktgottfr]

I am located in Calgary, Alberta. Thanks for the help!

So to get back to my original question, if hypothetically I use section VIII of the boiler code to design the pressure containing components of my device, are there materials with higher strength than A36 steel that I could use? My reading of section VIII suggests that I can use, say a 4135 steel forging for my pressure containing component and that would give me the relatively high allowable stress of 34.3ksi at room temp...

It might sound like a simple question, but there is another engineer here that is telling me that a36 is as strong as is allowed for pressure containment...

-Kristjan

 

[SnTMan]

ktgottfr, under ASME Sec II, Part D, there are any number of materials stronger than A-36 and permitted for Sec VIII, Sec III, Sec I work. Perhaps you can get a look somewhere.

From the discription of your part it sounds like could be condsidered a "manufacturers standard" for which you can kind of pick your methods.

Agree, talk to your AI.

Regards,

Mike

 

[Canadieng]

I am in Edmonton, and I believe your colleague is confused, unless there is more to the story - if this fitting is really as simple as you imply, you can use higher allowable strength materials for Category H fittings. I deal with ABSA quite a bit.