Mr.. Mani,
The intent of ASTM A 923, Method C. is for detecting the presence of detrimental intermetallic phases in duplex stainless steels. The acceptability criteria for corrosion resistance is the by weight loss. The presence or absence of corrosion attack in this test is not necessarily a measure of the performance of the material in other corrosive environments; in particular, it does not provide a basis for predicting resistance to forms of corrosion not associated with the precipitation of intermetallic phases.
Various experimental results
have shown that , major intermetallic such as sigma phase 0.1-0.5% (volume fraction) are easily tolerable by various duplex and super duplex S.S grades. However, when the volume percentage reaches a level of about 1% a detrimental influence is observed for both alloys. A percentage of σ-phase below 0.5% is perfectly acceptable provided pitting corrosion is the main concern.From severity point of view this test is less severe than ASTM G-48A test.
Hence for application of DSS for refining and petrochemical environments, this test is suggested by various codes, e.g API -938C. and NACE MR-103. Usually, if welded well with welding products of reputed manufacturers (e.g Metrode as mentioned) specimens should not fail.
What was the ferrite count and the volume fraction of intermetallics in the weld coupon??. Was it calculated ???
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of E.S.Mani
Sent: Wednesday, February 20, 2013 4:30 AM
To: materials-welding@googlegroups.com
Cc: sivaselvam@kpoc.com.my
Subject: Re: [MW:16823] Pitting Corrosion Resistance Failure in DSS
Thanks for your info,
Yes the client spec was saying to do ASTM G 48 C.
Yes we used the PQR as per the consumable recommendation.
We used GTAW.
Dear siva,
Cold pass means second pass or next to the root pass.
Mani
Dear Mani,1. Before planning for PQR, You have to confirm from Consumable Manufacturer that, Do they grantee their consumable to pass Corrosion test in accordance with ASTM 923 C, As most of Consumable Manufacturers prefer to test according to the ASTM G 48 Method (Which is actually standard for Pitting Corrosion Test, While ASTM 923 C is for Intergranular Corrosion Test).2. Does your Project specification calls for Corrosion Test as per ASTM 923 Method C. If not, then go for ASTM G 48 C?3. If ASTM 923 C is the requirement, then I shall suggest you to change Consumable Brand ( You may select Sandvik)4. Which Welding Process, did you use?, If possible MIG can be useful, But there is no special restriction for using GTAW, SMAW or SAW.5. Conduct PQR Wedling according to all the recommendations of Consumable Manufacturer including those, shielding / purging gases & current ranges etc.6. There is special technique with DSS & SDSS, depositing thick root pass and thin cold pass (as fast as welder can weld it).7. Did you monitor Oxygen Level in Backing gas (if used) during welding, It should be less than 50ppm or according to Consumable manufacturer?RegardsTariq Hussain.--
On Wed, Feb 20, 2013 at 6:08 AM, E.S.Mani <maniesbk@gmail.com> wrote:Dear Experts,
We are welded DSS A790 UNS S31803 Pipe to pipe PQR welding and we sent it for Mechanical test. But we found PITTING.
The details are below and i attached the test result also.
Material : A 790 UNS S31803 (Pipe to Pipe)
Size : 4" X 8.56mm
Filler Used : ER2209 (Metrode) 2.4mm
Max. Interpass : Below 50ºC
Max. Heat Input : 1.2 KJ/MM
Test Method : ASTM 923 Methode C (22ºC – 24HRS)
Now we are planning to do the PQR again. So please give me you idea to avoid the failure again.
Thanks.
--
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Regards,
E.Subramanian
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Regards,
E.Subramanian
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