Stainless Steel Welding Problem - Annealing Colors 1

[prady22]

Experts,

Regarding the above mentioned subject would like to solicit your kind advice.

For the running 8 times consecutive stainless steel welding skill test conducted here at the workshop results were all unsuccessful.
The test conducted was for the 2 NPD S80S A316L for positions 2G and 5G. The filler wire used was 2.0 mm A316L brand name Leeden Powerweld Sdn Bhd.

In the beginning the WPS parameter was strictly observed. The result was a failure due to the appearance of annealing colors of blue and red.
Linde action of rejecting the joint was based on the Linde specification, AX_W-SC_2401 (EN) Metallic Piping Systems AG/UG. Herewith attached this document can find in Chapter 5.8 Piping Prefabrication clearly mention for the paragraph, The prefabrication completion status is achieved if,: SS welds are metallic bright (outer and inner surface), straw yellow will be accepted.

The team from my side did some adjustments and experimenting as per site team suggestions.

First, was on the flow rate of Argon gas was checked that while welding is performed it is within range as per WPS.

Second, was Amperage of current for monitoring the heat input during welding was observed that it is within range as per WPS.

Third, was the Argon gas purity which was confirmed 99.99% as per supplier material certificate.

Fourth, cleaned the joint with the acetone was also observed.

Fifth, the interpass temperature was controlled to below 70 deg C before continuing the pass.

Sixth, leak test on the Argon gas hoses and bottle manometers by soap test was conducted to ensure that purity is maintained.

Seventh, Keep evacuation time of other gases e.g. oxygen when purging (2 min) and also after removal of tape.

Eighth, gas detector was also used to monitor quantity of oxygen inside the pipe during purging to check for the purity.

An improvement was observed. There was a reduction and diminishing of the annealing as seen and checked by our QC inside of the finished product. But still unable to perfectly eliminate the unwanted annealing colors. This as per Client and it's still unacceptable. 100% shall be free of blue and red annealing colors to avoid corrosion.

And also one question is, how about field joint welding? How to determine 100% free of unwanted annealing colors? And talking about weld fusion as per visual examination by QC is not a problem here.


Perhaps with all your experience and knowledge can share something to resolve this problem.

Regards,
Prady

 

[metengr]

The bottom line is your getting oxidation on the surface of the stainless steel from exposure to oxygen. You need to improve gas shielding and purging before welding, assuming all other parameters are correct.

 

[EdStainless]

Oxygen and water are your issues.
I am guessing that your acetone has a lot of water in it, how long has that container been open? You need to use small containers of acetone and keep them capped.
There may be a lot of moisture on the pipe surfaces and some warming of them may help.
Don't purge with higher flows, just purge longer.
What O2 level are you looking for at your purge vent?

Don't just test hoses and meters, replace them. If the hoses are a year old or have been allowed to sit unused (especially in the sun) then they are too permeable. I have seen it caused by hoses, connections, regulator diaphragms, and flow meters.

We inspect the ID of every weld for color, anything other than a light gold color is rejected. We use a borescope to inspect the IDs. Yes this is in the field, every weld.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[gtaw]

Heat tint is caused by exposure to air and/or other sources of contamination. Often overlooked is the need to clean the ID of the pipe prior to welding.

I typically do an initial cleaning operation using acetone and then follow that with a 90% isopropyl alcohol flush. That applies to both the OD and the ID. I also insist on wire brushing the joint, inside and outside with a clean stainless-steel brush. It amazing how people often forget the tools used for cleaning and preparing the joint must be clean and the gloves worn must be clean as well.

Air tools can be a source of contamination if the exhaust is not directed away from the surfaces being welded. After all, the source of compressed air is lubricated with oil and contains considerable moisture unless it is filtered to remove contaminates. Some air tools exhaust to the rear and have provisions for a tail hose to direct the exhaust away from the tool.

In service repairs can be more of a challenge due to the potential for internal contamination by surface debris, oxides, fluids, etc. that can volatize during welding. The volatiles can be a source of contamination that can be easily overlooked.

As for the shielding, a magnehelic can be used to eliminate the possibility over pressurizing the system while purging. The volume of the purge must displace the volume of the system by a factor of 7 or more to reduce the oxygen content to a level conducive to oxide free welds. An oxygen monitor is a worthwhile investment. A trailing cup may be needed to protect the exterior surfaces from oxygen until the base metal and weld have cooled sufficiently.

Good luck.


Best regards - Al