Stainless stell for high temperature 2

[kangomath]

Dear experts,
My company will run a Sulfuric Acid Plant project. Our licensor require 316L material as converter and ducting shell material which will operate at 600 Celsius.

I know 316L having good resistance in sulfuric acid. But with that high temperature, will 316L suffering intergranullar corrosion since it will be exposed into sensitization temperature range?So, what is the main reason to choose this material for this operation condition, and what should I do for welding procedure?shall the welding procedure tested also with corrosion test simulating operation condition? Your opinion and experience is highly apreciated..

 

[EdStainless]

What part of the plant are you talking about?
What acid concentrations?
If you are talking good 316L (<0.02% C) then it will sensitize, but not much.
I would be more concerned about the formation of intermetallic in the welds related to residual delta ferrite.
I might look into welding with 316Ti

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P.E. Metallurgy, consulting work welcomed

 

[kangomath]

Thank you Ed...
Actually it is a converter which will convert H2SO3 into H2SO4 in gas condition which I have no idea the concentration, and the temperature is 600 celsius.
And yes, I preffer like 316Ti for this application..

 

[EdStainless]

Try reading this.

MS-1: Materials Selection for Sulfuric Acid

Converters
The converter operates at high temperature (up to 625ºC [1,157ºF]) in an oxidizing
atmosphere. Sulfur dioxide from the burners enters the top of the converter through
Al-coated steel or type 304 ducting. Traditionally made of brick-lined carbon steel or
cast iron, converters today are usually fabricated from type 304H (S30409), often with
a minimum 0.04% carbon to provide increased high-temperature strength. Type 304L
(S30403) does not have adequate strength at the temperatures used in modern con-
verters. Sensitization of high-carbon stainless steel will occur throughout the struc-
ture during service, not just at the welds. This is not a problem, however, since the
stainless steel is never in contact with wet chlorides, except possibly from the outside
during the very short startup and shutdown periods.
Recent work has shown that type 304H (S30409) stainless steel exhibits accelerated
corrosion at temperatures above 630°C (1,166°F) in converter atmospheres. The high
silicon stainless steels were found to be more resistant under these conditions, but the
effect on mechanical properties of silicon-rich phases was thought to need further
study. If converters are operated at temperatures consistently above 630°C (1,166°F),
it is likely that materials that have better high-temperature corrosion resistance than
304H (S30409) will be needed.9


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P.E. Metallurgy, consulting work welcomed

 

[ShabsRBI]

In Refinery FCCU operation, SS304H material is used for cyclones and operating temperature remains high as 730 Deg C. At this temperature SS-304H suffers Sigma phase embrittlement and loses low temperature toughness. High temperature exposure of SS-304H produces Sigma phase and that shall be determined through Replica metallography. Sigma phase at the weld is normally more than the base metal. Initial stages of Sigma phases are tolerated but after long service of approximately 20-25 year Sigma phases presence warrants replacement of Cyclones and its attachments.