Hi Rutvik,
ASTM A 995 GR.4A(DSS) is 22Cr-5Ni-Mo-N(UNS-J92205) duplex casting. The matching chemistry for this product is ASME -SA-240 S31803 (in plate), and in pipes SA-790. However many a times castings would have a lot of unbalanced chemistry due many factors e.g.: manufacturing technique, shapes, irregular cooling rates, responses to heat treatment etc. That's why welding on duplex castings are always more difficult then welding on plates or pipes.
Duplex stainless steels are very good alloys with a good combination of enhanced mechanical properties and corrosion resistance when properly balanced in composition and properly heat treated. Generally they develop a range of approximately 30 to 60% ferrite with the balance austenite.
In your case, the manufacturer have a welding procedure which meets the requirements of ASME Sec-IX. But client's requirements or any specification requirement are over and above the code requirements, due to the facts that they are service application specific. If client requires the flowing tests as mentioned below, your vendor (casting shop) has to redo the qualification test. It may be done by preferably weld a supplementary test coupon to the existing PQR and performing tests such as ferrite count, pitting corrosion , detection of sigma phase and other intermetallic phases. It is not necessary to repeat the mechanical tests.
In order to perform a supplementary weld coupon:-
· Weld a test coupon following exactly the welding parameters of existing and qualified PQR. Duplex S.S requires a good control on welding heat input.
· You may use casting materials (if available as spare) or plate or pipes of equivalent composition and properties.
· Perform ferrite count - ASTM-E-562
· Detection of any intermetallic/sigma phases-ASTM-E-923
· Pitting Corrosion Test- according to ASTM G-48
· Meet any other test requirements as asked by your client.
ASTM –A-995 Clause -12. recommends stress relieving of duplex S.S castings, if the weld repair is major (i.e. if the depth of repair is over 20% of actual wall thickness or 1 inch, whichever is smaller). Should the weld repair calls for stress relieve as per A-995, then a completely new PQR shall be established, meeting all Sec-IX mechanical tests, plus the other tests as mentioned above. Usually ASTM-A-488 is the guiding document for qualification of welding procedures for casting repair.
Note : ASTM-A-995 –Supplementary requirements S-1 through S-51 describes some of the additional testing as required by your client.
Hope my response clarifies the issue.
You may download these free documents for your reference:-
· http://www.imoa.info/_files/stainless_steel/Duplex_Stainless_Steel_2d_Edition.pdf. This is a comprehensive document on duplex S.S.
Thanks.
Pradip Goswami, P.Eng.
Welding & Metallurgical Engineer/Specialist
Component Integrity Section.
Engineering and Training Services
Ontario Power Generation Inc.
Res:-88,Garth Trails Crescent
Hamilton,Ontario, L9B2X1,Canada
Email-pgoswami@sympatico.ca
Email-pgoswami@quickclic.net
Tel-905-679-9677
-----Original Message-----
From: materials-welding@googlegroups.com
[mailto:materials-welding@googlegroups.com] On Behalf Of rutvik dixit
Sent: Tuesday, February 23, 2010 12:45 PM
To: materials-welding@googlegroups.com
Subject: [MW:4366] DSS REPAIR WELDING PROCEDURE
Hi everyone,
I need to inspect the castings of ASTM A 995 GR.4A(DSS). Now mfr. is having the approved/qualified wps for repair work. This material (castings) is
having other requirements like ferrite content, pitting corrosion resistant test, sigma phase, total of intermetallic phases. The qualified wps doesn't consist these metallurgical tests, but having all mechanical and impact test. can mfr. go ahead with this wps for repair work? wps is having any
relationship with these type of metallurgical tests?
With regards,
Rutvik
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