RE: [MW:5799] RE: 5792] FW: 5772- ASTM G 48 testing for SDSS

Dear Sudhakar,

 

The welding parameters are ok including heat input. Pickling is not necessary for DSS welds unless you notice discoloration of welds and moreover it is not required for welding procedure coupons. Hence, pickling and passivation shall not be required for PQR coupons.

 

Confirm the following before you test for G48.

 

• PRE for filler metal shall have 40-45, minimum shall be 40
• Check ferrite content in the deposited weld metal (35-65)
• Minimize root gap to 2 mm (to avoid Ni dilution)

 

In order to achieve better corrosion resistance, follow “Cold Pass” technique for second layer/ pass for SDSS welding. In general for CS and LAS, the second layer/pass is called hot pass, where as in DSS it is called cold pass. It means that the welding current for second layer shall be 75% of root pass in order to achieve better phase balance (austenite+ferrite) and also to have better corrosion resistance in root, which is more critical (wetted part). Cold pass shall be with single bead like root pass in order to avoid dilution and related microstructure changes.

 

See attached article would explain more detail on cold pass technique. In case of cold pass, the dilution will be minimized and also alteration of microstructure in the previously deposited weld metal. Also lower heat input ends with higher % of austenite in the weld which is essential.

 

Follow all other parameters as mentioned in the trailing mail. Hope it would be helpful.

 

Regards,

 

L. Prabhu kumar,

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Sudhakar
Sent: Wednesday, June 30, 2010 10:46 AM
To: materials-welding@googlegroups.com
Cc: <materials-welding@googlegroups.com>
Subject: Re: [MW:5798] RE: 5792] FW: 5772- ASTM G 48 testing for SDSS

 

Dear Mr.Goswami and Mr.Prabhu,

 

Thanks a lot for the inputs.

 

10 days before i have taken a trail to check this test. 

The details are as follows

Material: A 790 UNS 32750 

Size: 2"/160 (8.56mm thk) 

Position: 6G 

Interpass temp: 100 deg max

Heat input maintained: 0.7 to 1.21 kj/mm

Filler wire: ER 2594, (1.6 mm for root, rest 2.4mm)

Shielding gas and purging gas: Argon(98%)+N2(2%)

Flow rate: shielding 10 to 15 LPM

Purging: 8 to 12 LPM

 

For the joint preparation we have used the SS discs and after welding we did the pickling.

 

Susprisingly in the result the weight loss observed was 41.67 gm/m2 and there were pits observed on the root side. I was shocked to see the result and I'm not understanding why it happened. 

Before sending to Lab we did not check the ferrite count.

Thanks again..

 

Sent from my iPhone

On 30-Jun-2010, at 12:35 PM, "Prabhu Kumar L" <l.prabhukumar@saipem-india.com> wrote:

Dear Sudhakar,

 

In addition to the restriction mentioned in the trailing mail, control on heat input is more critical in Super DSS materials such as UNS S32750. Based on my previous experience on these materials, I would suggest heat input limit should be 1- 1.5 Kj/mm for smaller thickness and 2 Kj/mm max for thicker sections.

 

As Mr. Goswami suggested, the ferrite to austenite ratio also critical for G 48 testing. Heat input increases, the rate of cooling would be reduced, and in tern more % of ferrite formation in the final weld. It means that we are allowing more time to transform austenite to ferrite when we use increased heat input. In general the % of ferrite in the weld should be 35 – 65%.

 

Using lower heat input would minimize the formation of ferrite which is more important for SDSS welds.

 

Regards,

 

L. Prabhu kumar,

---

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of pgoswami
Sent: Wednesday, June 30, 2010 6:42 AM
To: materials-welding@googlegroups.com
Subject: [MW:5792] FW: 5772- ASTM G 48 testing for SDSS

 

 

Dear Sudhakar,

 

ASTM G48A(72 hrs), or and modified versions(24 hrs) is the most common specified corrosion test for duplex or super duplex S.S. This test is considered to be a check of the metallurgical condition of the steel rather than  its performance in any service environment.  The ferric chloride solution is very aggressive and resembles actual industrial service environments.

 

For base metals specified test temperatures vary considerably and are 22.5–30°C for 22Cr duplex and 35–60°C for 25Cr duplex(A790, S32750). In ASTM G48A, 72hour test period is stipulated, however shorter version  24hour  exposure is also used  in the industry.

 

For 22Cr duplex, the experience from service as well as from testing according to various specifications is extensive and shows that a test temperature of 22.5–25°C is suitable to ensure that materials properties after welding and heat treatment operations are within the limits expected for 22Cr duplex.

 

For 25Cr duplex, a combination of laboratory test results and service experience, although not as extensive as for 22Cr duplex, strongly indicate that   50°C is a suitable test temperature for solution annealed base metal products.

 

For welded coupons of 32750 typical recommendations of testing temperature of 40⁰C , and either 24 or 72 hrs of exposure time, with no pitting  be present  20X magnification.

 

From my past experiences in such materials I could advise you on these aspects:-

 

·         Choose the base metal and weld filler metal with ASTM G48A  or G48 C (determination of CPT)  test done typically @ 50°C

·         Monitor welding parameters closely, and stick to the welding heat input of 2-3 KJ/mm criteria. Super Duplex 32750 have a tendency to form excess ferrite, which may to turn to sigma phase, for thick section welding. Composition of shielding and backing gas(Argon+ Nitrogen) would be critical.

·         I presume that  ASTM G-48A test is not the only test you’re going to perform. If not look out for the test results of Ferrite count test, a good ferrite to austenite ratio  and relative absence of sigma phase could be a good way to start for corrosion test.

·         Surface preparation of samples could affect the test results. Generally after cutting the samples,  the serrations and undercuts should   be  ground  and the specimen should be ground to a 120-grit finish. Under all circumstances use new blades and avoid mix up with blades cutting C.S or LAS.

 

 

The  test for welded coupons  is  required to be done in as welded conditions, thus the above guidelines would be of help. I have a attached an article on  G-48 test and it’s implications.

 

Thanks.

 

 

Pradip Goswami,P.Eng.

Welding & Metallurgical Engineer/Specialist

Ontario Power Generation Inc.

Email-pgoswami@sympatico.ca,

pgoswami@quickclic.net

 

 

-----Original Message-----

From: materials-welding@googlegroups.com

[mailto:materials-welding@googlegroups.com] On Behalf Of Sudhakar

Sent: Monday, June 28, 2010 8:43 PM

To: materials-welding@googlegroups.com

Subject: [MW:5772] ASTM G 48 testing for SDSS

 

Dear members,

 

What are the extra special precautions that need to be taken for conducting ASTM G48 Method A test @ 40 deg C for A 790 UNS 32750 material.

 

Rgds

Sudhakar

 

Sent from my iPhone

 

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