SS 316 L Thru weld corrosion 7

[JayCarp]

We have the second of our Ozone plants on line. The plants are processing / using the same source water.
This is all well and good but on the second plant on - stream we seem to be experiencing through the weld leaks.

The pipes in question operate at ~ ~ 4 p H.

We have not had problems with the first plant and this has
been a real curve ball -

We have about 40 joints leaking and this is totally new to
my experience as I have worked with austenitic stainless
in ASME Section VIII and Piping and have not experienced this since 1968 -

Has anyone experienced anything similar ? ? ?

 

[EdStainless]

316, pH = 4, slightly warm water, as welded.
I figure that you can handle about 10 ppm Cl before pitting kills you.
A heat of material with a bit lower Nitrogen, or welds that have a bit more oxidation and maybe 5ppm Cl would be the limit.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[HEC]

As always EdStainless, you have nailed it. Look at the material certification for each of the installations for the pipe. Also look at the weld procedure. If the second plant has been welded at a higher heat input the weld will be more susceptable to pitting attack.


Mark Hutton

 

[SJones]

Take a look at the molybdenum contents too. The first installation may well have had a reasonable amount of molybdenum compared with the second facility. Borderline performance can be tipped one way or another by molybdenum and, of course, suppliers like to aim at the low end of the range.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[strider6]

maybe it's a problem of welding sensitization, intergranular corrosion, or maybe a wrong filler materials. To say something it's necessary to make a failure analysis of the weld.

S.

http://www.corrosionist.com

 

[EdStainless]

I see 316L fail in warm potable water service with great regularity.
You should have some standard metallographic work done. Base metal and weld filler chemistries are easy. Looking at the degree of coring (segregation) in the welds would be my next step.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[mcguire]

Welds are susceptible especially to pitting corrosion when sulfur is high, 0.007% to 0.015% is common, to facilitate weld penetration. It doesn't show up in the tubing itself because the longitudinal welds have been annealed.

We all really need to move away from 316 to lean duplex, such as 2101 and 2003. We don't need to make Norilsk richer than they are already. The 10% nickel in 316 is a tremendous waste of money and of a scarce resource. It takes end users, such as the members of this forum, to make this happen.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[unclesyd]

I have will have to disagree with some of the above posts concerning chlorides and 316L SS piping. We have a waste system with over a mile of pipe where the Chloride levels vary from 500 to 1000 ppm with pH in the range from 2 to 7 with a temperature around 150F. This line runs 24/7/365.

I have never seen pitting in the welds on this line. The corrosion rate in this system is very low < 0.005 ipy, measured.
I would suspect that you have a problem with weld contamination that is causing your problem. I have seen SS welds diluted with about every alloy around.

One other problem I've seen is where you have water line, in our case cooling tower water, where there is considerable downtime creating stagnate conditions where MIC has preferentially attacked the welds.

 

[metengr]

There is really not enough information to provide any diagnosis of this problem. Have you removed a section of the weld and pipe to confirm if corrosion pitting is confined to the welds or are you just observing this visually as external leaks at weld joints?

Remove a section of the failed line w/a butt weld and have it analyzed by a competent metallurgical lab.

 

[EdStainless]

McG, I haven't seen S in those levels causing problems unless you are talking about very thick sections. Usually the benefit of smoother more uniform welds helps more than the S hurts. Over the 0.015% level you do start to see reduction in pitting resistance.

Syd, 316 can be very unpredictable, there are so many environments that are so close to depassivating that minor details can push you over. With constant flow and no deposits you can run seawater in 316L, but stop the flow for a few hours and you will destroy the lines. Local oxygen levels and pH are everything.
You are fortunate with your system. It is well beyond a reasonable application for 316L. I would consider 2205 suitable, but nothing lower.

Minor variations in weld practice can be a killer. Poor back shielding, too high or low of delta ferrite levels, too high of heat input, and about 10 other things can all cause significant reductions in pitting resistance in the welds or weld HAZs.

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Plymouth Tube

 

[strider6]

this is one example of corrosion due to poor welding.
HEAT TINTS ON STAINLESS STEELS CAN CAUSE CORROSION PROBLEMS

http://www.corrosionsource.com/technicallibrary/nidi/literature/pdf/14050.pdf

S

http://www.corrosionist.com