technical advice needed

[finiteinjustice]

Dear forum members

your help & technical insight is needed for following two cases illustrated below, which i am facing right now as i write:

kindly confirm if PWHT is required for monel 400 piping (weld filler: monel 60) in HCL or caustic environment. In our plant. we have seen severe corrosion of monel weld build up in such environment in our caustic scrubber column in the isom unit of ms plant in our refinery (monel weld build up was severly attacked & reduced to porous honeycomb type dendritic structure). Kindly also suggest the details of PWHT.

Note: In normal cases PWHT is not required as monel is a solid solution alloy & is readily fusion welded, normally in the annealed condition. As the heat affected zone (HAZ) does not harden, heat treatment is not usually required after welding

Also kindly confirm if PWHT is required for SS446 sheathed skin thermocouple welding to T91 heater tube material with inconel-82 filler wire.

if possible kindly mail me or suggest some concrete technical backup at finiteinjustice@gmail.com

with regards
"J"

[pg1916]

NB: I have posted a few attachments in my email to your gmail account:-finiteinjustice@gmail.com

Hi,

I came across your query in the forum. I did good dig out of information on this issue. This looks to be a case of selective leaching or dealloying.

Monel 400. is a Ni-Cu alloy, and a single phase alloy, where Nickel and Copper are soluble to each other at any composition. The flip side of this alloy is Cupro-Nickel (70Cu-30Ni). That’s why this alloy, Monel 400 is preferred in many acidic environments and Cupro-Nickel is very popular in sea water applications.

There are reported cases of dealloying of Monel 400 alloys in refinery especially in HF and HCl media. See the attached extracts from API-571 and the other attachment for information. To make the matters worse, iron dilution in Monel welds can seriously aggravate corrosion resistance. Hence one has to look into:-

· “Fe” content –undiluted in the weld metal (verify the CMTR)

· Weld cleanliness—ensure use of clean stainless steel brushes for interpass cleaning.

· Avoid large weld beads, weld with lower heat put and follow multi bead- techniques. This may help in avoiding any localized segregation.

· Ensure that root passes are welded only by GTAW (with Argon purging)



Note:- Monel welds does not require PWHT strictly as per ASME BPV Code. If it is overlaid I have seen clients insist for Stress relieving, often as a process requirement. Straight Monel# Monel butt welds usually does not call for PWHT.



I would advise you to send a piece of failed weld for failure analysis and look for the following:-

· Optical micrography at the failed surface

· SEM/EDAX at the analysis at the failed surface.

· Indicate the most possible mode of failure, i.e. dealloying or any other.



In addition please specify the design conditions of the scrubber:-

· Materials of construction

· Design pressure/Temperature

· Operating Pressure/Temperature

· Operating Media and the concentrations



This would help to make the correct analysis and solution of the problem.



Regarding the second query:- Also kindly confirm if PWHT is required for SS446 sheathed skin thermocouple welding to T91 heater tube material with inconel-82 filler wire. Please follow the guidelines of

· API TECHNICAL REPORT 938-B -Use of 9Cr-1Mo-V (Grade 91) Steel in the Oil Refining Industry.



Generally any P-91 welding , especially for refining environment would call for PWHT.



I would appreciate a sincere response from your end to my email.



Thanks



Pradip Goswami,P.Eng

Senior Engineer/Specialist(Welding-Metallurgy)

Machine Dynamics & Component Integrity Dept.

Engineering & Training Services Division

ONTARIO POWER GENERATION Inc.

34 Regional Road 55, Nanticoke, Ontario,N0A1L0

Tel:-(519) 587-2201, Ext 3107--in Nanticoke

(416) 231-4111, Ext 5925--in Kipling,Toronto

Fax: (519) 587-6825

Email-pradip.goswami@opg.com.

[finiteinjustice]

Dear Mr. Goswami

thanks a lot for the effort you have put in to answer to the queries of a total stranger. and thanx again for the attachments & your observations on my queries.

i too agree with your assertion.

however i will send you a detailed & sincere response later in the eveing through my email.....

"J"