4" Thick but soak for only 15 min at PWHT temp?

[bmoorthy]

Hello All

This is a ASME Sec VIII Div 1 vessel. 4" thick. Forged (SA 765 Gr 1).

The vessel is internally overlayed with Inconel 625.

We are not able to put the whole vessel in the furnace.

We explored the following possibilities.

Butter the edges with Inconel 625 (E Ni Cr Mo 3).
Heat treat the shells independently (One shell at a time)
Then for welding the Butt joint (between the shells) with full alloy weld (E Ni Cr mo3) and NO PWHT.

The question is how long should i soak the the individual shells (at 593 deg c).

1) One school of thought is "15 min only". This is Because the governing thickness is the cladding thickness (Even if the Clad is a part of design calculation).

2) The second scool of thought is soak assuming the governing thickness is 4" (That is total soak time is 2hours 30 Min).

I think i will get an answer if i know what is the governing thickness (For Buttered Joint)

is there some interpretation or relevent clause.

 

[metengr]

Your post is confusing. Is the vessel going to be constructed via cladded shell segments? If so, it makes no sense because why would you subject the Inconel 625 cladding to a PWHT that could risk loss of corrosion resistance especially for a P-No 1 Group No 1 vessel base material?

If you had reviewed Part UCS, Table UCS-56 you could have followed Note 2 (c) 5 where the P-No 1 vessel could have been fabricated, PWHT in whole or in segments, followed by the application of the Inconel 625 corrosion resistant cladding over the entire vessel ID surface with only a 200 deg F preheat for the first pass of the cladding, and NO PWHT.

If the shell segments already have been clad and now you are going to weld the shell segments together to construct the vessel, you could butter each end of the carbon steel weld prep and make the vessel welds using Inconel weld metal – again no PWHT would be required only a 200 deg F preheat.

 

[JoeTank]

Metengr,
Are you saying that these P1 4 inch thick vessel segments can be welded together w/o PWHT?

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[bmoorthy]

Metenger


Yes the situation is complex.

We are in this situation due to dimensional constraints and strict final tolerances (We want to avoid distortion, even 1mm cannot be tolerated, hence the objective is to perform PWHT to code compliance and if possible reduce the soak time,in full compliance of the code requirement)

PWHT is being done by the virtue of CODE UCS 56 requirement (Not because the items are overlayed, but because of grove thickness)


There are 6 shells. The Id is Overlayed with Inconel (625)

In PQRT we have established the retention of corrosion resistance of Inconel 625 by testing as per G 48 and G 28 (practice A). Hence Corrosion resistance is not an issue.

The question is regarding the girth seam (Circum seam category b joint)

Sequence proposed

1) Weld the shell 1 Complete inside Overlay(No Nozzles or head). Then Butter the edge of the shell 1 then PWHT the shell 1.

2) Weld the shell 2 (No nozzles or head). Then butter the edge of shell 2 then PWHT the shell 2.

3) other shells and nozzels and heads are welded separately and heat treated separately (Soak time as per governing thickness of the grove weld).
We have supporting weld procedures for all the possible combinations that the job might encounter.

The question is,
A) while i PWHT the shell 1 (With Buttering) what should be my soak time. is 15 minutes enough or should it be 2hrs and 30 min
B) while i PWHT the shell 2 (with Buttering) what should be my soak time.is 15 min enough or should it be 2 hrs and 30 min

C) Shall 1 and shell 2 after welding will not be heat treated after girth seam welding since we are going to use full alloy weld. The weld is between Incoloy and Incoloy with Incoloy. (Using the procedure QW 283 fully complied)

 

[metengr]

bmoorthy;
If you butter the entire weld prep surfaces of the 4" thick P-No1 shell segments with Inconel, using a 200 min F preheat, as per UCS-56, you do not need to PWHT after buttering. The buttering can be treated as a corrosion resistant weld overlay as per Note 2 (c) 5 for P-No1 base materials. Once the buttering of the entire weld preps are completed, the girth weld could be completed using a qualified WPS for P-No43 to P-No43 base material using F-No 43 filler metal with no PWHT. This is a very expensive way of fabricating the vessel. Also, NDT those buttered surfaces before you deposit the girth welds.

I would assure a 1/4" thick butter layer on the entire 4" thick weld prep using a 200 deg F preheat.