Re: [MW:20153] RE: Black spots on DSS Weld Joints.

Mr. Rao:

Chinese products shall be tested and inspected carefully...

In our project, we are dealing with this "Chinese material quality" issue almost on daily basis.

Each day we receive a new material at site, we know that it will turn to another headache...
Most of the samples (which client has taken) have failed in mechanical tests.

Materials without identification is the least of our problems (we can easily reject them and move on)...!!!
It's the so called "good quality" Chinese material which causes problems. They have certificates, identification etc. but they usually fail in tests...!!!
 
The most recent one is LTCS flange (A350-LF2) material with 4J absorbed energy (Impact test), who could possibly imagine that...?

Be careful with those Chinese products.

Regards

Ramin Kondori

Sr. QA/QC Engineer

SINOPEC

r.kondori@petroyada.com
+98-2123592322
+98-9132150320

On Tue, Feb 18, 2014 at 7:49 PM, pgoswami <pgoswami@quickclic.net> wrote:

Mr. Rao,

 

Please see my answers to your queries.

 

Thanks

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgoswami@quickclic.net

pgoswami@sympatico.ca

 

 

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Vasantharao
Sent: Saturday, February 15, 2014 1:46 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:20108] RE: Black spots on DSS Weld Joints.

Dear Sir,

We use Pure Argan  - 99.998%  with moisture <5PPM, Oxygen <5 PPM as per Gas MTC.-- That's fine.

We use separate shop for DSS welding for avoiding contamination from CS welds/ grinding. --That's fine 

Welders aware of Acetone cleaning of joint, filler wires etc. -- That's fine, and should be done.

Purging gas  O2 level continuously monitored with instruments till completion of welding  (maintained <0.03%).--This is good but still try to keep lower, (<0.02%). 

Random checks during welding  observed inter pass temp. some time more than 150 Deg.C  but <200 Deg.C -- That's fine.

Some time we preheat to 50 Deg.C  to remove moisture. - That's fine.

This problem typically we observe in 6" & 8" Pipes, others are satisfactory (lower dia). --This tells me that there're issue with some pipes, assuming that same welding filler (brand, batch and through cleaning  as mentioned above) is used for welding.

Is it dark spots are any inter metallics? ( As per leterature it forms at 300-700 Deg.C, generally during welding, this range not encountered). -- Intermetallics are detected only under microscope, they can not be interpreted by visual inspection alone.  2209 is a relatively lean filler metal (wrt ER 2593 and 2594 filler). Hence I would not suspect much intermetallic. However as a cross check you may take replicas or put one small section of the welds with dark indications under the microscope to see if it contains intermetallics. Note to get  to the  intermetallics, you have to do the grinding , polishing and micro etching, which will remove the dark spots. A better approach is to see the section under SEM & EDAX, which may be done on as it is condition. EDAX will tell what the contaminant is , if metallic or hydrocarbon

Pickling & Passivation will be costlier, management may reluctant to go for it. --There's no other way if the steel is grossly contaminated with any chemicals  

Is there any effect of TIG nozzle sizes, Moisture condensation at regulators?. --I do not think so. 

Some of the Pipes are received from China, is there any material chance?. --I do not want to be prejudiced.But where's there's bulk purchase/ trading, such mishandling  would happen and  would  produce bad results while welding. If the products are directly purchased from the mill, post this problem directly to the manufacturer. Otherwise if it's purchased through dealers( with many sub-agents)  you may have a hard time to get the correct answer.

 

This problem typically we obseve in 6" & 8" Pipes. --If the quantity is not much get them replaced with products from some reputed mill 

Your suggestions noted, i will work on those.

Thank you for your valuable suggestions.

regards

P.Rao.

+968 93883351

On Friday, 14 February 2014 7:57 AM, pgoswami <pgoswami@quickclic.net> wrote:

Hi Mr.. Rao,

 

These black spots are essentially the products of contamination in the weld metal.There may not be a single reason towards this .It may happen as follows:-

• Welding Fillers :- The drawing lubricants e.g graphite could contaminate the welds and cause  these spots to be formed. Through acetone cleaning of all the fillers should be done before welding. Also fillers with oxidized tips should be used following  removal of the oxidized tip(by cutting).

 

• Shielding gas: check the purity of the gas, it should be 99.95% or more.  Premixed gases say Ar+N2 may contain traces of moisture , which  may increase the oxygen potential and the resultant oxidation of the puddle. As you said  earlier the "O2" content was  well below 0.2%.. Assuming the fact that  for shielding gas everything was under control it would be always advisable to check the right purity of the shielding and purging gas, prior to welding.

 

• The condition of the pipes:- Duplex pipes should always be pickled  and cleaned at the mill. If not done at the mill, it's preferred to pickle the pipes and remove the excess scale or oxides in the fabrication shop. Usually such oxides could be very microscopic and very difficult to remove by grinding. Excess oxides may introduce contamination in the weld.Also cross contamination during grinding could harm the welds.

 

The dark spots are bad , with potential for pitting during procedure qualification testing or while put in service.

 

Let me know if it helps.

 

Thanks

 

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgoswami@quickclic.net

pgoswami@sympatico.ca

 

 

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From: Vasantharao [mailto:vasantharao@yahoo.in]
Sent: Wednesday, February 12, 2014 11:57 PM
To: pgoswami
Subject: Fw: Black spots on DSS Weld Joints.

Dear sir,

Can you give you suggestions on DSS dark spots as group member are not responding.

Is there any problem with dark spots. Why it forms. 

regards

P.Rao

On Wednesday, 12 February 2014 1:38 PM, Vasantharao <vasantharao@yahoo.in> wrote:

Dear Experts,

We observe Dark spots on Welding of Duplex Stainless Welds.  

Material is : UNS S31803 ,  Filler Wire for root - ER2594, rest ER2209.

Sample pictures are attached for reference.

Oxygen level in shielding / Purging maintained well below 0.2%.

Interpass <150 Deg.C

Pl. share your valuable information.

Thank you.

P.Rao

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