Hi Vignesh
Looks like I read your post incorrectly in terms of the pipe schedules. - OK
The SS 14" Sch 120 is 27.79mm thick, so after tapering the thicker CS pipe down to that thickness, then according to ASME B31.3, you will need to perform PWHT on the CS. No thickness of 316 SS will require PWHT. Strictly speaking, the weld will need PWHT according to the code. See 331.2.3(b):
(b) Heat treatment of welded joints including both
ferritic and austenitic components and filler metals shall
be as required for the ferritic material or materials unless
otherwise specified in the engineering design.
You will notice that it gives you an "escape clause": "unless otherwise specified in the engineering design"
To clarify how this clause could be implemented, see 331.2.2:
331.2.2 Exceptions to Basic Requirements. As indi-
cated in para. 331, the basic practices therein may require
modification to suit service conditions in some cases.
In such cases, the designer may specify more stringent
requirements in the engineering design, including heat
treatment and hardness limitations for lesser thickness,
or may specify less stringent heat treatment and hard-
ness requirements, including none.
When provisions less stringent than those in para.
331 are specified, the designer must demonstrate to the
owner’s satisfaction the adequacy of those provisions
by comparable service experience, considering service
temperature and its effects, frequency and intensity of
thermal cycling, flexibility stress levels, probability of
brittle failure, and other pertinent factors. In addition,
appropriate tests shall be conducted, including WPS
qualification tests.
-------------------------------------
This means that you can dispense with the PWHT requirement, as long as the appropriate engineering has been done to confirm that the resultant weld will be able to perform the specified service required of it.
Other options are:
1) Simply perform the PWHT. Most modern "L" grade austenitic stainless steels will not sensitise during the PWHT process, so would be OK, as long as you do not apply too long a heating cycle. This would obviously have to be proven during the welding procedure qualification testing. Also note that due to the large difference in thermal expansions between the CS and SS, there will still be rather high residual stresses in the welded joint following the PWHT, but certainly any hardened zones in the CS should be tempered. Because of the resultant high residual stresses, there may in fact not be much benefit to the PWHT, so it is often better to take other measures, and show through "engineering" that PWHT is not needed, or desirable. (See discussion above.)
2) Use a buttering technique. Here you would typically use an alloy that does not need PWHT, but can withstand it, to butter the CS weld surface. (Typically Ni based alloys of the "Inconel" type.) After buttering the weld surface of the CS, perform the required PWHT on the buttered end of the CS pipe. Then using the same Inconel filler, weld the SS pipe to the buttered CS pipe. No PWHT need be applied to the final joint.
As noted by some of the other people in this post, these types of situations need to be evaluated on an individual basis, to make sure that the resultant weld will perform the service required. This will need a detailed knowledge of the service / design conditions of the pipe.
Hope this helps.
Regards
Niekie
This is one time I'm gunna agree with the majority and strongly suggest the OP gets some professional advice as Al suggests! Even suggestions are unethical with the limited info available on a forum.
Hi 46.00
I agree that more "engineering" needs to be done, (as stated a number of times in my post) but often the best way to get that message across is to show why the engineering is necessary. If we do not know what we do not know, then how will we be able to come to the conclusion that we do not know? Forums like this help us with the process. I have certainly been helped in this way on this very forum!
Regards
Niekie
In so many ways that is a typical human problem, not relaying total, adequate, and/or applicable information so those we are depending upon for answers can come to the proper conclusions and resolutions.
Hopefully the suggestions and information presented are giving that opportunity to the OP. I know I am learning more from the thread.
Have a Great Day, Brent
hey NIEKIE
THANX FOR UR VALUABLE COMMENT IT HELPED ME ALOT.....I WENT THROUGH PARA (b) BUT still this line is confusing "filler metals shall
be as required for the ferritic material or materials unless otherwise specified in the engineering design"
can u help
Hi Vignesh
I think you are reading this incorrectly. You need to read the whole paragraph, then you will see that it is saying that all components of the joint must be subjected to the PWHT required for the ferritic material. It does this by listing the different components of the joint:
1) The ferritic material
2) The austenitic material
3) The filler metal
It is NOT requiring you to use any specific filler metal. You are free to use any filler metal that will result in a joint that will be serviceable.
Hope that helps.
Regards
Niekie
By vignesh5585
Date 04-22-2013 15:37
Edited 04-22-2013 15:42
ok ..thanxx again ..niekie
according asme 31.3 pwht is required rite.....Our designer has specified that only CS material above 19 mm should be subjected to pwht but he didnt mentioned anything about dissimilar metal,when we had tlak abt this then he replied refer asme 31.3 for further detail....
Niekie,
Take a look at Vignesh first posting. It has been edited on April 21, which means that in April 21 Vignesh corrected the pipe thicknesses stated on his first posting.
That's why both you and me referred to Sch 80 and 120, that later turned to be Sch 120 and 140.
No mistake from our part. It's Vignesh who later on realized that the thicknesses were stated incorretly. No problem. ERRARE HUMANUM EST, as ancient Romans said.
Giovanni S. Crisi
Hi Prof Crisi
Thanks for pointing that out. I thought age was getting to me!
Regards
Niekie
All guyzz
I apologize for incorrect info given by me......
cheers