Corrosion on SS 304 welding area
Corrosion on SS 304 welding area
(OP)
Dear All,
I'm developing a solar water heater which combines the collector and storage tank together, heating portable water directly. The product has been made, and tested. The problem we found after 6 months testing is pitting/crevice corrosion on the top of SS 304 tube (welding area).
My case is:
- SS 304 long tube welded on the bottom and top
- portable water in the SS tube, regular working temp. 35-210F.
- Pressure <90 psi
- Max temp. 600F when the SS tube is empty and baked under the sun.
There is very little corrosion found at the bottom or in the middle of tube. Pitting/crevice corrosion is only found at the top around welding area. The solar hot water was rarely used when testing. I suspect that the pressured steam with chlorine in portable water is causing the corrosion, and the S.S. material structure was damaged at the welding area.
My question is:
-Any coating material can be applied at the top of welding area inside the S.S. 304 tube? but it can not contaminate the portable water under high temp. and pressure.
-Any welding process or procedure can be used without destroy S.S. 304 material structure in this case?
Thank you very much for your help and advice!
Dixie Solar
I'm developing a solar water heater which combines the collector and storage tank together, heating portable water directly. The product has been made, and tested. The problem we found after 6 months testing is pitting/crevice corrosion on the top of SS 304 tube (welding area).
My case is:
- SS 304 long tube welded on the bottom and top
- portable water in the SS tube, regular working temp. 35-210F.
- Pressure <90 psi
- Max temp. 600F when the SS tube is empty and baked under the sun.
There is very little corrosion found at the bottom or in the middle of tube. Pitting/crevice corrosion is only found at the top around welding area. The solar hot water was rarely used when testing. I suspect that the pressured steam with chlorine in portable water is causing the corrosion, and the S.S. material structure was damaged at the welding area.
My question is:
-Any coating material can be applied at the top of welding area inside the S.S. 304 tube? but it can not contaminate the portable water under high temp. and pressure.
-Any welding process or procedure can be used without destroy S.S. 304 material structure in this case?
Thank you very much for your help and advice!
Dixie Solar





RE: Corrosion on SS 304 welding area
Look into passivating the area, and using brushes and other tools that only touch stainless material/welds. Should decrease any cross-contamination.
James Spisich
Design Engineer, CSWP
RE: Corrosion on SS 304 welding area
What is the tube specification? Were the tubes solution treated? Were the tubes cold finished?
RE: Corrosion on SS 304 welding area
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Corrosion on SS 304 welding area
The corrosions were found around the top of circumferential weld area. Attached is a pic of cutting section on the top of the tube. You can hardly see the corrosion on that area. But it is very serious. Almost every tube has tiny holes leaking at the top when the pressure is on. The rust you see outside of the tube is caused by leaking afterwards.
There is no solution or any treatment when welding the top piece on the tube. Can you suggest any treatment to improve the welding, and prevent the corrosion?
Some people say I have to change the material to 316 SS because of chlorine in portable water. But there is no leak or very little corrosion found at the bottom or in the middle of the tube. This leads me to believe 304 may be still OK. I just need some coating to block the steam at the top weld area, especially the inside triangle area at the top.
Thank you very much "stanweld"
Any input, suggestions are much appreciated.
RE: Corrosion on SS 304 welding area
Maybe weld an incoloy 800 top piece is the cost effective way to do it?
I found "Incoloy 800H/HT alloy was intended for high temperature structural applications. The nickel content makes the alloys highly resistant to both chloride stress-corrosion cracking and to embrittlement from precipitation of sigma phase." on Internet
Please comment.
RE: Corrosion on SS 304 welding area
RE: Corrosion on SS 304 welding area
How are you making the circ. seam? I doubt that the gas backpurge is adequate.
RE: Corrosion on SS 304 welding area
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Corrosion on SS 304 welding area
The gas backpurge maybe inadequate during the top circ. welding. But now I more intend to believe that 304 SS probably can not stand the steam corrosion at the top.
RE: Corrosion on SS 304 welding area
RE: Corrosion on SS 304 welding area
RE: Corrosion on SS 304 welding area
One more question:
What kind of welding structure do you suggest to weld the "safe-end, either duplex SS or incoloy 800" to the top of 304 SS tube? any treatment before welding or any special technique to weld those two different SS materials together?
Appreciate all your help.
RE: Corrosion on SS 304 welding area
"You see, wire telegraph is like a very long cat. You pull his tail in New York and his head is meowing in Los Angeles. Do you understand this? Radio operates the same way: You send signals here, they receive them there. The only difference is there is no cat." A. Einstein
RE: Corrosion on SS 304 welding area
The regular working temp. is 35-210F with pressure about 65 pis.
We tested our product from June-Dec. in Texas. Nobody was using the solar hot water. I believe the pressured steam constantly on the top caused the problem.
RE: Corrosion on SS 304 welding area
2. It is most likely that the high ferrite number of standard 304L lead to welds that have much worse corrosion resistance than the bulk metal.
3. Modify the design to remove the tight crevice from a non-flushed area. You will only trap and concentrate impurities.
4. Moving to a lean duplex will give you slightly better pitting resistance than 316 along with MUCH better CSCC resistance. And a lower price. There are a bunch of such alloys on the market, feel free to mix and match, 2003, 2101, 2102, 2404, and whatever has been added this month.
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Plymouth Tube
RE: Corrosion on SS 304 welding area
Thank you very much for your posting.
The current design is concave top for easy and fast welding process.
Convex design with duplex SS (or other alloys you suggested)at the top seems the solution from all the postings here. The top has to be long enough so the circumferential welding line is under the water to protect 304. This solution will increase the material cost quite bit and the difficulty to weld as the wallthickness is only 0.8mm and it's a very long tube (about 7' long).
Is there any coating material I can use to fill the concave gap inside the tube to cover the weld area completely? The pitting/crevice corrosion all happended at the top weld area. The 304 top itself seems OK.
RE: Corrosion on SS 304 welding area
Moving to lean duplex will not change the price much, especially if you go to 0.7mm, the alloys are much stronger.
The welds in a duplex retain a higher percentage of original corrosion resistance than do austenitic alloys.
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Plymouth Tube
RE: Corrosion on SS 304 welding area
Can you let me know the name of manufacturers who are doing automatic butt weld of different SS tubes? We are considering to sub-contract this job out.
Thanks,
Dixie Solar
RE: Corrosion on SS 304 welding area
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Plymouth Tube
RE: Corrosion on SS 304 welding area