alloy steel

Date 02-22-2007 14:39

Not much info provided...sounds like a good question to ask your engineering dept.

Regarding the weld procedures:
SA-335 Grade P11 is a ASME P4 mat'l and the stainless's are P8 mat'ls.
Changing from the P4 to a P8 mat'l will obviously require a different WPS/PQR, ..do you intend to substitute and join the stainless pipe directly to the P4 mat'l as well?

By chall

Date 02-23-2007 13:33

I thought about answering this yesterday, but there is more to it than I can remember.

One thing for certain that needs to be considered: Look in either ASME Section IID or B31.1 and compare the respective stress values of all the metals at the applicable system design temperature. If the stress value of the P8 materials are at least as high as the P4 material, than the materials may be successfully used unless there are other restrictions. My recollection is that some stainless materials may not be used in "wet" environments (but I don't remember the fine details).

I do know that some P8 materials are definitly unsuited for the high temperatures usually present when P4 materials are the "normal" selection; so I expect that you will discover one may work and the other won't.

Charles

By pyman4407 Date 02-27-2007 08:56

thank you very much for helping me

By nosetackle (**)

Date 02-24-2007 05:40

not much information provided,

which fluid is passing through SA-335GR P11 pipe, i.e fluid class. What temperature exactly ? What is the NDT class for that pipe class, Working and test pressure for that pipe classes.

these questions are vital, without knowing that nobody can give an answer.

as far as i know sa312 tp 316 working temperature is up to 300 degC. if your working temperature is close to 300 degC or over, is not possible to use 316
may be you can think to use martensitic and ferritic stainless steels, such as "420",which has high heat and wear resistance up to 600degC.

for high temperature usage incaloy or inconel type materials are used.

but in anycase SA335grP11 will be cheaper for you.

Regards,

T

By pyman4407 Date 02-27-2007 08:57

thanks for all helps

By MBSims

Date 02-24-2007 22:04

My response would be "No - not unless your design engineer has evaluated the change and says it is OK."

Stainless steels expand at a different rate than P11 does as it heats up to the operating temperature. This means both the diameter and pipe length changes at different rates. A dissimilar girth weld between P11 and 304 or 316 will have additional thermal expansion stress across the weld. The changes in length at operating temperature may increase bending loads at elbows that may either be too high (resulting in failure) or require changes to the pipe support load settings. And the allowable stress values for 304 and 316 are much lower than P11 for a given temperature, so the minimum pipe wall thickness required will be higher.

I recommend you not make such a change without consulting a design engineer.

By js55

Date 02-26-2007 15:31

I'm a little worried that such a question would be asked in this forum. This is strictly a design engineering issue.

By MBSims

Date 02-27-2007 04:31

Yes, I share that concern sometimes. But, if the question is being asked to validate an idea that someone wants to bring to their engineering group, then this forum is a good sounding board. I have no problem with that sort of question and would not discourage someone from asking. I respect that the person asking decided to get someone else's opinion rather than do it without asking.

By js55

Date 02-27-2007 14:37

Well said Marty. And I stand corrected. Always better to ask. And SS is not without a history in power and high temp applications. I don't believe the 300C limitation on 316 is valid. Maybe some old timers can remember heavy wall SS in high temp steam applications. I believe the reason they moved away from it was of course the coefficient of thermal expansion, and economics. The bainitic Cr Mo's are a much more economical and less problematic choice.