Stainless Worms / Leaking T 316 L Piping System 1

[JayCarp]

This is in follow -up to my previous post regarding
a 316 L stainless piping system which has developed
a whole bunch of small leaks -

Was in the receiving area today looking at some new ASTM
A -312 Grade 316 L . Pipe size is 14 " Schedule 10 S. While the O. D. of the weld seam
was smooth as you would expect , the weld on the inside
of the pipe had the appearence of an area which worms had
crawled over. Going to look at this with more higher power
instruments Monday.The depth of this phenomena is about .005
to 0.010.

Has anyone ever seen this before ? Will follow up with
pictures. I was thinking possibly " Low Moly " as I have seen heats of 2.04 to 2.06 Mo which is cutting it kind
of thin -

Is this an acceptable condition ? The MTR 's say that
the pipe passed A - 262 Practice E.

 

[MikeHalloran]

Reports are easy to forge.

Did this material come from the same supplier as the stuff that already leaked? Consider using a different source, at least until they get the message.



Mike Halloran
Pembroke Pines, FL, USA

 

[EdStainless]

The texture may just be from teh welding process and not a problem in it itself.
2.01% Mo is common. When you do checks you will often find 1.98% and that is still within the check allowance.
Take a magnet and see how magnetic the welds are. The residual ferrite level may be very high since this pipe is probably underannealed. High residual delta ferrite will be much easier to attack than 316L.
Sounds like you need a procurement specification.

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Plymouth Tube

 

[mcguire]

A major suspect should be high sulfur. See if the sulfur is over 0.010%. Sometimes pipe makers like such high sulfur levels to make the welding of the longitudinal pipe seam easier. This is ok for welds that are subsequently annealed, but it is bad for girth welds done after annealing.
I have seen tests that show high sulfur 316L, i.e. 0.003% or higher, can have its corrosion resistance lowered to that of 304 by welding.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[EdStainless]

In well made clean welds S as high as 0.016% has little negative impact on corrosion resistance.
Contamination, high ferrite, and surface oxidation are all much more serious issues.
Passing a PractE just means that they have low carbon.

What country was this pipe manufactured in?

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Plymouth Tube

 

[mcguire]

Ed
I wish I knew how to post the chart from Suutala in Stainless '84, but it showed 316L having four times the weight loss in FeCl3 after welding, without annealing for 0.020%S versus 0.002%S. I have seen similar etsts showing a reduction in critical pitting temperature of 10C for tubing and corroberating results on pitting potential.
Unannealed MnS inclusions have serious chromium depletion around them. Sulfur makes nice looking welds but it comes at a price.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[unclesyd]

I have to side with mcguire on this one.
We had two processes where P had a significant effect on the corrosion rate of 304L and 316 SS.
Our general specification for 304L is .008 S and the normal request is to get material as low as possible for use in the highly corrosive areas.
The process where the low S is required is HNO3/Organics at 120C. If SS is used in this area there is also a requirement that the C be 0.015 max with the S being 0.008 and P be 0.012 max. Work to verify that S had an affect on the corrosion rate came about due to some work with 2RE10 and some plate with 0.010 C. As this process material can not be tested on the bench, we used the Huey test to verify some field observations of differences in corrosion rates.
The test samples of material was supplied by Sandvik and Eastern. The samples were graded out based on the Carbon and evaluated based on the C and S. We ran over 60 Huey tests and had the plant statistical group evaluate the results. There results were that C had the biggest effect and that the lower C plus low S were synergistic in lowering the corrosion rate. We have no welding problems with the low S material.

The other process was the handling of molten Adipic Acid at 190C using 316 equipment. The specification for 316 used in this process was 0.015 S max. It was noted that as we increased the temperature of the process a few degrees there was a noticeable difference in the corrosion rates the equipment. Laboratory testing revealed that S played a major role in the corrosion rate of 316 in this process.

Fortunately the molten Adipic process is gone and Ti has replaced the 304L in the highly corrosive areas of that process.

 

[EdStainless]

Well if you are using 316 to handle FeCl or HNO3 then the S and P levels really do matter, but in normal pH mild chloride environments were 316 is actually used there is not an appreciable effect from S. I have done electrochemical work in 500ppm Cl and pH=6 and you can't tell that S has any effect.
I have made nitric acid grade 3XX tubing, and yes we worked from 0.005% S for that type of product. That probably accounts for less than 1/2% of SS in use.
Weld penetration in autogenous welds with low S is a bear. You will wider welds with more severe segregation and coring.

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Plymouth Tube

 

[mcguire]

Ed, without sounding contentious, I still say why pay a significsnt premium for the Mo in 316 (over 304)and then negate it by having excess sulfur? For pitting resistance that's what happens.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[BUTCHCWIQAM]

I have one question... when the pipe was tested where did the water come from? and I would love to see pictures
After you answer the question I will elaborate on my theory