RE: [MW:16854] Pitting Corrosion Resistance Failure in DSS

Dear all,

 

I have experienced suppliers who provide duplex pipe, fitting and flanges which were found to have low ferrite content as measured by in situ ferrite scope. The low ferrite content suggest the presence of intermetallic phase, which was confirmed by microscopic examination as per ASTM A923 Method A. Intermetallic phase formation is caused by improper heat treatment of duplex stainless steel.

 

Are there any mill certificates for the pipe which shows the amount of ferrite content? If not, perhaps you could conduct ferrite scope measurements on both the weldment and pipe body to see if there are low ferrite readings. The acceptable range of ferrite content in duplex stainless steel is 35-65%. If low ferrite readings are observed, then the weldment and pipe could be send to a lab to conduct ASTM A923 Method A to determine the amount of intermetallics.

 

Intermettalic phase  formation will cause reduction in the corrosion resistance.

 

 

Regards

 

Siva

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of pgoswami
Sent: Friday, February 22, 2013 10:20 AM
To: materials-welding@googlegroups.com
Cc: maniesbk@gmail.com
Subject: RE: [MW:16837] Pitting Corrosion Resistance Failure in DSS

 

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 ???

Appreciate your feedback.

 

Thanks.

Pradip Goswami,P.Eng.IWE

Welding & Metallurgical Specialist

Ontario, Canada.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

 

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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

 Dear Mr.Tariq,

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

On Wed, Feb 20, 2013 at 1:27 PM, Tariq Hussain <tariqhussain632@gmail.com> wrote:

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?

 

Regards

 

Tariq 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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