Black Spots on DSS Welding

[Mahmood Alhinai]

Dear Experts,

Kindly, refer attached photos and clarify what could be the reason of block spots appeared throughout DSS welding surface.

 the welding was carried out as per the approved WPS and approved welder, the DSS filler wire was approved (Bohler / ER2594 / ER2209). Pipe material: A790 UNS 31803

Welding process: GTAW

Thanks & Regards,

Mahmood

[patni engineers]

Slag no weld surface

Clean Each weld pass by Ss wire brush.

Check filler wire properties

Use UHP ( high pure argon gas as shielding Gas)

Regards,

Chandrakant

B.E Mech.

ASNT Level II RT/UT/PT/MPT/CSWIP

GST -27AMOPP5962A1ZS
Patni Engineers. Mumbai. India

PED/2014/68/EU

welding shop AD2000/DIN EN ISO 3834

IBR Approved 

Factory Addreess- Pl Call 

--
https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-weld...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CANV5n6iefLaN0vsBJQ3L64_Z6PC38kHXY4nGDL_HjK_UxRG78A%40mail.gmail.com.

[Babur Khan]

Greetings,

We faced same issue, we did Radiography and surface examinations. 

Possible root causes are shielding gas during welding.

Muhammad Babur Khan

Sent from my iPhone

On 13 Nov 2025, at 3:07 PM, patni engineers <patnien...@gmail.com> wrote:



To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CAKLNAG7ZF-SVmp6L1POu1o7ACgUZbYAbFrSGBWbxJmd00J2M%3DA%40mail.gmail.com.

[Bala Murugan]

Hi Mr.Mahmood,

• The black spots on the DSS weld are mostly due to lubricant residue or surface contamination on the filler wire or pipe. 

• Surface Coating/Lubricants: GTAW filler rods (ER2594, ER2209) are frequently manufactured with surface coatings or lubricants to aid wire feeding and protect from corrosion during storage; these may cause visible black spots when burned off.

• Shielding Gas Issues: Even minimal exposure to atmosphere due to improper torch angle, gas cup movement, or inadequate coverage can cause oxidation spots.

• They are superficial and can be minimized by cleaning filler rods and workpiece before welding, and ensuring proper shielding gas coverage.

• Post-weld cleaning (pickling or brushing) further helps remove any surface spots.

Thanks & Regards,

Balamurugan

IWE

--

[Tamil]

This issue called Heat tint. Try to cool rapid or clean picking and passivation method 

To view this discussion visit https://groups.google.com/d/msgid/materials-welding/25CE9578-B897-4467-965F-4161F2865FB5%40gmail.com.

[Nambirajan Avudaiappan]

As per SABP-A-022(Source :- SABP-A-022)

When stainless steel piping or components are manufactured they are normally subjected to a final high temperature solution heat treatment (typically at 1050ºC) followed by water quenching. This leaves the material in the solution annealed condition which is the optimum for corrosion resistance. This heat treatment gives a poor quality high temperature oxide film on the surface which is quite thick, porous and cracked. During manufacturing, this oxide film is normally removed by pickling and passivating the surface in oxidizing acids. The oxide film which is formed at low temperature, either in the passivating solution or just by exposure to air, is thin and dense, giving good protection to the stainless steel. The as-delivered piping is therefore in an optimum condition, with a solution heat treated microstructure and a well-passivated surface oxide finish.

When welding is carried out, the metal close to the weld is reheated to high temperatures, from the melting point at the fusion line to lower temperatures through the HAZ. An unprotected HAZ which is exposed to air during welding will therefore show a high level of oxidation. Characteristically, it would be black in color and in the worst condition may be visibly thick and porous. This oxide is far more easily broken down than the original passivated surface and there is a zone of metal under this oxide which is lower in chromium content relative to the bulk metal.

Therefore, the HAZ has to be protected from re-oxidising at high temperature during the welding process. This is done by shielding around the weld using an inert gas to exclude air, thus preventing oxidation whilst the weld metal and HAZ is hot. Once the weld is cooler, the HAZ will re-oxidise slightly at lower temperatures but this oxide film is a more protective film than the high temperature oxide film. This ‘heat tint’ oxide formed at the HAZ at lower temperatures is so thin that it forms interference colors, forming characteristic blue or rainbow colors. AWS D18.2:1999 addresses factors affecting weld discoloration inside a 316L austenitic stainless steel tube. It presents a color guide (Figure 2) relating degree of discoloration to oxygen content in the backing shielding gas. The heat tint oxide can be identified by a number corresponding to the oxygen level in the shielding gas. A straw-to-yellow heat tint (chart no. 3) is considered desirable but a blue tint up to chart no.6 is acceptable for standard applications.

Best regards,

Nambirajan

--

[Joshi Babu]

Dear Mr. Mahmood,

Please advise your welder , before welding, take a piece of emery paper and rub the entire surface of TIG wire then start welding. Please proceed with Pickling and passivation after this.

Joshi Babu

Sr.QCE

98001420  

--

https://materials-welding.blogspot.com/
https://www.linkedin.com/groups/122787
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-weld...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/materials-welding/CANV5n6iefLaN0vsBJQ3L64_Z6PC38kHXY4nGDL_HjK_UxRG78A%40mail.gmail.com.

--

                       Thanks and Regards

JOSHI BABU