Corrosion Pitting Prevention on 304/316 SS
Corrosion Pitting Prevention on 304/316 SS
(OP)
Hi all,
My company has come across a situation of corrosion pitting inside of the stainless steel tank right along the weld. The welding materials is 316L SS welding rod to weld 304 SS sheetmetal.
The application of the tank is to heat up different liquids in the tank and transfers heat for hot water or hot air use. The liquids that needs to be heated up are antifreeze or domestic water (city water) at high temperature of 200 ºF.
I have done some research of preventing the pitting corrosion. The methods that I have come across are as following:
Selected the materials with known resistance
Currently, we are using 304SS and 316SS will be the next selection due to higher corrosive resistance. However, the researches that I have conducted state that the 316SS will last 6 months to 1 year longer compared with 304SS. Furthermore, the price is 78% higher.
Control pH, chloride concentration and temperature
Due to our application, it is impossible to avoid that.
Cathodic protection and/or Anodic Protection
I am not sure about this method since there are other materials welded onto the SS sheet metal.
Use higher alloys (ASTM G48) for increased resistance to pitting corrosion
As it is stated in the first method.
Another way is to prevent the pitting corrosion is to have a steel coating with porcelain or epoxy. However, it worries me of the high temperature antifreeze in the tank.
All the suggestions are welcome and appreciated. Once again, thank you for your inputs
My company has come across a situation of corrosion pitting inside of the stainless steel tank right along the weld. The welding materials is 316L SS welding rod to weld 304 SS sheetmetal.
The application of the tank is to heat up different liquids in the tank and transfers heat for hot water or hot air use. The liquids that needs to be heated up are antifreeze or domestic water (city water) at high temperature of 200 ºF.
I have done some research of preventing the pitting corrosion. The methods that I have come across are as following:
Currently, we are using 304SS and 316SS will be the next selection due to higher corrosive resistance. However, the researches that I have conducted state that the 316SS will last 6 months to 1 year longer compared with 304SS. Furthermore, the price is 78% higher.
Due to our application, it is impossible to avoid that.
I am not sure about this method since there are other materials welded onto the SS sheet metal.
As it is stated in the first method.
Another way is to prevent the pitting corrosion is to have a steel coating with porcelain or epoxy. However, it worries me of the high temperature antifreeze in the tank.
All the suggestions are welcome and appreciated. Once again, thank you for your inputs





RE: Corrosion Pitting Prevention on 304/316 SS
If they are pitting from weld oxide (heat tint) then it can be prevented. Using good weld shielding and then a pickling paste to clean them would do the job. Do not let anyone grind them to clean them, this does not work.
You could try to salvage the current tank (if the pits are not too deep) by grinding them out using a fresh grinding wheel. Then cleaning the ground material with a pickling paste. My hunch is that some of the pits are over half way through if you can see them. This tank is history.
Another alloy option is a lean duplex stainless steel. Alloys with names such as 2101, 2003, 2202 are all candidates. They have pitting resistance similar to 316 (or a little higher), the welds (use 2209 filler) do not loose as much corrosion resistance as in 304/316, and they are much stronger so you may be able to use thinner material (if hte design allows).
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Plymouth Tube
RE: Corrosion Pitting Prevention on 304/316 SS
Thanks for your reply and input.
One of the tanks has returned to us due to the problem of pitting corrosion. So, the pits have already started. We didn't have this problem before until recently when we change the material. So your guess is as good as mine. Probably the poor quality of stainless steel.
As you state, the pits start at on the line of the heat tint. I will look it up the suggestion of using good weld shielding and pickling paste. Pardon me for lack of knowledge on welding manufacturing processes. Is there a general procedure of applying the pickling paste?
I will also consider the option of lean duplex stainless steel. Not sure the price is in the acceptable range for 2101, 2003, 2202.
Once again, thank you for your input and suggestion.
RE: Corrosion Pitting Prevention on 304/316 SS
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion Pitting Prevention on 304/316 SS
RE: Corrosion Pitting Prevention on 304/316 SS
RE: Corrosion Pitting Prevention on 304/316 SS
Thanks
RE: Corrosion Pitting Prevention on 304/316 SS
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion Pitting Prevention on 304/316 SS
As far as we know, we recommend antifreeze with mixture of 50/50 solution with water. What the customer claimed is that they have put different brand of antifreeze with mixture of water. However, once the product is out of the door. There is no real way to find out what liquid they actually put in the tank.
The pickling paste basically clean the surface of the welds by acid treatment to remove high temperature scale produced in welding. Will it work better to use pickling paste first and then passivation?
RE: Corrosion Pitting Prevention on 304/316 SS
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion Pitting Prevention on 304/316 SS
This is such a wonderful reading and reference. Thank you for the information.
RE: Corrosion Pitting Prevention on 304/316 SS
I have one more quick question about the pickling and passivation.
I understand it is almost a standard to do the pickling before passivation since the acid that they use in pickling is hydrofluoric acid (HCl) mixture, and the passivation is usually diluted nitric or citric acid (H3C6H5O7 ). I also understand the purpose of picking and passivation.
However, is it possible to do the passivation and the pickling at the same time in one step? does that mean there will be a different acid for both passivation and pickling? If there is, what would be the name of this kind of solution?
Thanks
RE: Corrosion Pitting Prevention on 304/316 SS
Steve Jones
Corrosion Management Consultant
http://www.linkedin.com/pub/8/83b/b04
All answers are personal opinions only and are in no way connected with any employer.
RE: Corrosion Pitting Prevention on 304/316 SS
Once again, another amazing information to clarify my question to passivation. I did not know that the passivation has other definition other than forming a surface film. What I have found is that the traditional method of passivation is to have a film on the surface of the metal. I will look into both ASTM standards and the attachment that you provide. Once again, thanks for the clarification.