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At waht temperature does the Heat tint occur 1

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bmoorthy

Mechanical
May 29, 2003
457
We have Stainless steel piping

Application

Offshore: Oil and gas.

1) Some lines are subjecte to 85 Deg C
2) Some line are subjected to 133 Deg C and
3) Some line are subjected to 204 Deg C
4) Some line are subjected to 285 Deg C

We we peocure the material they are bright and after we fabricate them we Pickle and passivate them

My Question is

A) At what temperature the SS 316L will start getting the heat tint
B) If in any case, the heat tint is going to occur at "X" deg C and if we the end use is going to be at higher temperature, why take the trouble to Pickle at all?


 
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Sorry lots of typographical errors noticed

The questions are sent again for clarity

We have Stainless steel piping (SS 316L)

Application: Offshore: Oil and gas.

1) Some lines are subjecte to 85 Deg C
2) Some line are subjected to 133 Deg C and
3) Some line are subjected to 204 Deg C
4) Some line are subjected to 285 Deg C

When we procure the material they are bright and after we fabricate them, we Pickle and passivate them. The color of the pipe welds are white

My Questions are

A) At what temperature the SS 316L will start getting the heat tint
B) If, in any case, the heat tint is going to occur at "X" deg C and if we the end use is going to be at higher temperature, why take the trouble to Pickle at all?
 
The tinting that you see in service is staining, not oxide scale. These temperatures are below the heat tint range.
You pickle because it is the correct process to follow for optimum corrosion resistance.

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Plymouth Tube
 
a white color of the weld seems strange.. are you sure that you've correctrly pickled the SS?
heat tint is something that happens in air exposure and during welding...if it will develop in service and the service is corrosive then you've problems...
what is the service of these pipes?

Heat tint (temper) colours on stainless steel surfaces heated in air

S



Corrosion Protection & Corrosion Control
 
Is there a correlationbetween Heat tint and surface hardness in 316 and 304 material?

Will there be differnet tinting behaviour based on the Carbon Content

For example, if there is a pipe thet is 316L and another 316 and another 316H and another 316LN, all subjected to same heat service, would the tinting behaviour change amongst them or would they remain same.
 
it shouldn't make any difference. The surface finish will strongly effect the appearance, but the C and N will not.

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Plymouth Tube
 
I would say without seeing the pipe and welds you have probably slightly over pickled the pipe welds. The welds will normslly pickle at a different, faster, rate than the pipe proper.

If using HNO3/HF This can be caused by the HNO3/HF ratio being off. The percentage HF is too high or the HNO3 is too low.
The pickling solution is too hot.
As above the time in the bath is too long.
The white is really a very light gray if the welds are the proper material. I would check and make sure the filler metal is the chemistry.

Can you comeback with your pickling procedure like concentration, time and temperature?
 
Without seeing your setup for pickling I'll say that your HF is way too high and is way too aggressive and is attacking the weld metal. I would try to get your HF below 5% preferably 3%-4%. Also I would drop the temperature 50C.

If you had 20% HNO3 + 3% HF you would have what is referred to as a bright pickling solution. This solution normally used where you are attempting to keep a good finish and will do a good job on fabricated pipe.
 
Thanks unclesyd for the tip on temperature and on HF.
 
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