Internal corrosion 304L SS with domestic (drinking) water
Internal corrosion 304L SS with domestic (drinking) water
(OP)
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.





RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
1) Seems that the welder didn't do a good job. pict 21, you can see that the profile of the weld metal is nonuniform and seems that there is a pit jsut in the middle of the weld metal. This suggest that heat tint and sensitization could be the causes of your corrosion problems. In the same pictures seems to see an area of metal that has a different colour just where most of the pits are. After welding the SS should always be pickled and passivated expecially in potentially corrosive service.
2) You said that the chloride level in the water is below 1 ppm at the well and that there is a treatment with gasesous chlorine. One possibility is that the residual free chlorine after the tratmentis too high.
This a giudeline from BSSA:
"Oxidants based on chlorine (as a gas or more normally as a solution product of hypochlorites) or chlorides (ferric chloride) can promote localised attack.
Levels normally encountered in natural and treated waters are below 1ppm but this can be increased at the hlorination points or due to inadequate mixing in water treatment systems, where attack on stainless steels can then be a potential hazard.
Grades 304 (1.4301 / 1.4307) and 316 (1.4401 / 1.4404) may become vulnerable to free or residual chlorine levels above 2ppm and 5ppm, respectively."
http://
Stainless Steel Corrosion by Water
So is possible that you failure is due to a combination of poor welding and after welding operation and too high level of residual chlorine level in the water.
S.
Metal Corrosion
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water
With good ID shielding there will be NO discoloration at all, not even a little gold or yellow tint.
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Plymouth Tube
RE: Internal corrosion 304L SS with domestic (drinking) water
Here one company that test for MIC and has some very good information on their website. I would give Potter a call.
http://www.mic-test.com/home
RE: Internal corrosion 304L SS with domestic (drinking) water
If you switch to low sulfur, and 0.001% is easily obtainable, laser welded pipe, this problem will cease.
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Internal corrosion 304L SS with domestic (drinking) water
The bigger problem is the surface oxidation and the related Cr depletion.
Second behind the oxidation is the problem with residual delta ferrite in the welds. Not only does the ferrite have very low corrosion resistance but it also results in small electrical currents that attract and stimulate the growth of microbes.
If you try but welding low S pipe you will have larger welds with more segregation. I don't see the S (and MnS) being an issue until you get about four other problems sorted out. If this pipe is made from hot rolled strip then the MnS inclusions in the base metal are larger than the ones in your welds.
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Plymouth Tube
RE: Internal corrosion 304L SS with domestic (drinking) water
Chloride - 35.6 mg/L
Iron - 12.1 ug/L
Manganese Dissolved - 1.51 ug/L
Hardness - 259 mg/L
pH - 7.41
Alkalinity - 305 mg/L
Once pumped out of the deep well only chlorine is added to obtain a free chlorine level of ~1 ppm.
Pipe deposit elemental analysis
Appearance: Reddish Brown Pieces
Elemental analysis by X-ray Fluorescence
The sample preparation was: Dried at 105° C
Iron as (Fe2O3) 54 %
Chromium as (Cr2O3) 19 %
Calcium as (CaO) 2 %
Silicon as (SiO2) 2 %
Nickel as (NiO) 1 %
Sulfur as (SO3) 1 %
Total From XRF: 79 %
The results for the XRF analysis were normalized to Loss at 925° C
XRF + L925 = 100%
Elements Fluorine to Uranium were measured. The following common elements were not detected
or were below the reporting limit of < 0.5%:
Al Ba Cl Co Cu F K Mg Mn Mo Na P Pb
Sn Sr Ti V Zn
RE: Internal corrosion 304L SS with domestic (drinking) water
You didn't list a conductivity, but it must be higher than typical.
I don't think that you can expect 304 to cut it.
consider a lean duplex, LDX2101 or AL2003. They will have good corrosion resistance and not cost too much more than 316.
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Plymouth Tube
RE: Internal corrosion 304L SS with domestic (drinking) water
I agree 304 is a waste of money because of the useless cost of nickel, Ed. 2101 is a good call. I don't think we will ever agree on sulfur in austenitics.
Michael McGuire
http://stainlesssteelforengineers.blogspot.com/
RE: Internal corrosion 304L SS with domestic (drinking) water
RE: Internal corrosion 304L SS with domestic (drinking) water