TimboGMO
Mechanical
- Mar 12, 2003
- 21
My company has been using 304L Stainless Steel piping for domestic water service for approximately 10 years now. They began the use of this pipe based on recommendations from a few technical papers that the chlorine levels (1 ppm free chlorine avg.) were low enough to not cause corrosion problems in the pipe. The water we are using is cold (60 degF) deep well water with no treatment other than the addition of gasesous chlorine in a concrete storage reservoir. Piping affected by the corrosion we are experiencing is very far from the source of water therefore I do not think chlorine levels are not being exceeded over the levels required to keep the water safe to drink.
The corrosion we are experiencing is pinhole leaks as observed from the outside of the pipe. Once the pipe is cut open you can observe deposits (corrosion by-products or MIC?) where underneath the deposits is significant pitting that causes the pinhole leak. I have attached pictures below.
The pipe is 304LSS most likely welded with 308LSS rod, but I cannot verify as it was installed before my time here. The pipe appears to have been shielded internally with inert gas during welding since some of the pieces pulled out from cut pipe were in better shape and no, or very little "sugaring" was found.
Our boiler chemical company made some suggestions as to what could cause this. Their guesses were sensitizing of the base metal which should be ruled out since it is 304L. Incomplete penetration of the welds (possible at some points), heat tint causing giving lower corrosion protection (which you will get some degree of heat tint even with a good sheild - so why use SS at all if you can't get to this heat tint on the inside of pipe?), or MIC (can't confirm but the water is chlorinated). Velocity of water in this particular pipe may be low, but we have other lines experiencing the same problems that should have normal velocity numbers based on their flow rates.
Has anyone else experienced these issues with 304LSS and domestic water? If so, did you come to any conclusions for causes and resolutions? Right now we have moved back to ductile iron for SS lines for domestic water.
The corrosion we are experiencing is pinhole leaks as observed from the outside of the pipe. Once the pipe is cut open you can observe deposits (corrosion by-products or MIC?) where underneath the deposits is significant pitting that causes the pinhole leak. I have attached pictures below.
The pipe is 304LSS most likely welded with 308LSS rod, but I cannot verify as it was installed before my time here. The pipe appears to have been shielded internally with inert gas during welding since some of the pieces pulled out from cut pipe were in better shape and no, or very little "sugaring" was found.
Our boiler chemical company made some suggestions as to what could cause this. Their guesses were sensitizing of the base metal which should be ruled out since it is 304L. Incomplete penetration of the welds (possible at some points), heat tint causing giving lower corrosion protection (which you will get some degree of heat tint even with a good sheild - so why use SS at all if you can't get to this heat tint on the inside of pipe?), or MIC (can't confirm but the water is chlorinated). Velocity of water in this particular pipe may be low, but we have other lines experiencing the same problems that should have normal velocity numbers based on their flow rates.
Has anyone else experienced these issues with 304LSS and domestic water? If so, did you come to any conclusions for causes and resolutions? Right now we have moved back to ductile iron for SS lines for domestic water.
