SS 316 vessel changes its colour to brown after Heat treatment 1

[Momo1988]

Hi Everyone ,

After the heat treatment process of pressure vessel which shell material is SS316 as per client requirements , the colour of the plates had been converted from stainless steel known colour to brown colour which is refused from both AI inspector and client so :

1- Do you know any solution to remove this brown colour because we use Pickling and there no positive effect .

2- Any advise to prevent the next SS vessel from have these colour during heat treatment process .

Thank you in Advance

Your
Mohamed A.Fatah

 

[Vikko]

Brown color ? Is it rust ? In this case, pickling should be enough. Usually stainless steel change color also at weld joint locations, for the thermal heat effect, so that pickling (or other chemical surface treatments) can be done after, to reuniform the surface. If pickling does not work, I suppose only plating can be done, in case the customer does not want paint coating.

 

[Momo1988]

Very thanks Vikko ,

We will try another pickling technique but i wonder about plating ?
How can i make plating for stainless steel shell ?
And you talk about other chemical surface treatment beside pickling .

 

[metengr]

How did you perform the heat treatment on the 316 ss?

 

[Momo1988]

The pressure vessel is carbon 80 mm ( SA 516 Gr60 with 3 mm claded with SS 316 and we do heat treatment as below :-

Heat treatment as per UCS-56
MAX HEAT 222 C/HR
MAX NORMAL HOLDING TEMP IS 620 C
MAX HOLDING TIME IS 60 MIN
MAX COOLING RATE IS 280 C/HR

 

[Vikko]

Plating in hot dip molten Zinc is just an example, if the customer complain about the color. Or you can also do electroplating with Chromium, like motorcycle exhaust, that would give a mirror effect to the surface, very nice to see.

 

[metengr]

Unfortunately, the stainless steel cladding was exposed to PWHT that will degrade corrosion performance. The brown color is heat tint from exposure to atmosphere under PWHT. At this point, you need to determine if the corrosion resistance has been reduced based on expected service conditions. If I was the client, this is what I would require.

To prevent the next carbon steel vessel from having this problem, butter the carbon steel with 309L and PWHT. Once this operation is completed, the 316 stainless steel overlay can be deposited over the butter layer with no PWHT required.

 

[JStephen]

I was thinking molten zinc was a major no-no on stainless steel, and sure wouldn't recommend galvanizing something just to get rid of the color.

 

[SnTMan]

JStephen, thank you

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[metengr]

I would also not recommend any coating on the clad stainless steel surface, period. You need to remove the cladding and start over or determine loss of performance. This is a nonconformance and must be evaluated under your Quality Program.

 

[hacksaw]

Stainless does oxidize do to its iron content, it is harmless, if contamination is a worry, then passivate with acid wash

 

hacksaw,
Incorrect, and you are clearly uninformed on the matter of heat tint.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[DVWE]

MohammedAFatah,

Another suggestion for future prevention, if possible, would be to PWHT the entire vessel and perform the clad welding afterwards. In accordance with Table UCS-56-1 General Notes (b)(3)(e)

On a side note, are you certain of your PWHT time? You stated your max holding time is 60 min. You should be at a minimum time of 2-1/2 hrs for an 80mm vessel.