Methyl chloride Corrosivity vs. Alloys 3

[Guest102023]

I need to select alloys to resist small concentrations of methyl chloride (a.k.a. chloromethane) in a planned vapour recovery system. Some condensed moisture is also likely. What is the temperature limit for 2205 duplex in this service?

 

[cloa]

So what is an approximate description of the composition of the vapour being handled? What concentration of chloromethane?

 

[cloa]

What temperature?

 

[strider6]

if it's dry :

http://www.outokumpu.com/applications/corrosion/view_details.asp?name=ME06

if there is moisture i think you've to select another alloy.. these guidelines from NIDI can give u some good advice:

http://www.stainless-steel-world.ne...B9664DEF68CC68=0&bcsi_scan_filename=10020.pdf

S

Corrosion & Rust Prevention Control

 

[Guest102023]

Conditions in the initial transport line are ambient (-10/+35°C) and there is expected to be condensed moisture.
Later the mixture (which also contains inert hydrocarbons) will see temperatures as high as 90°C.

 

[EdStainless]

At ambient temp 2205 should have enough SCC resistance. At higher temp you will probably want to use a Ni alloy (C22, 59, or similar).
I would actually expect the worst pitting conditions at the highest temp that the mixture is still damp. When you get hotter then SCC is the driving concern.

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Plymouth Tube

 

[Guest102023]

Thanks, EdStainless

Is superferritic a viable option for the lower temp. range? I suspect poor impact properties will be a show-stopper though.

 

[Guest102023]

How does 904L compare to 2205 cost-wise?

 

[EdStainless]

904 will be steep, lots of Ni at $10.50/lb.
I know where 317LMN is, and 904L will be more than that. So I would estimate at least 6x the 2205 price.

-10C isn't that cold. If the tube walls are thin then a super ferritic may do the trick. (thin wall, cleaner micro, finer grain, lower DBTT)
What about mechanical and thermal shock?

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Plymouth Tube

 

[Guest102023]

EdStainless, can you suggest a grade of superferritic? With decent low temperature impacts after welding of course.

 

[EdStainless]

The only two being manufactured today are SEA-CURE and AL29-4C. And only SEA-CURE is widely used in Code applications.
Since SEA-CURE has a small amount of Ni in it, and slightly lower Cr, it does have a better DBTT.

The welding can be an issue. The key is using as thin wall material as possible and welding with Ni alloy filler.

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Plymouth Tube

 

[Guest102023]

Does SEA-CURE come in 8", sch. 10? I have worked with all kinds of alloys, but never ferritic SS. I was aware of the grain growth and impurity issues. I would had thought HAZ toughness would be the issue rather than the weld metal. MDMT in my neighbourhood would probably be around -20C/-5F.

 

[EdStainless]

I don't know of a source for that large of diameter material. Besides you can't get the walls that heavy at any diameter. We consider anything over about 0.035" to be heavy wall. (we haven't made anything larger than 4" od)

The ductility issues are in the HAZ, but the only fillers that work are Ni alloy.

If you need 8"s10 then it looks like you are back to looking at duplex grades.

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Plymouth Tube

 

[Guest102023]

That's settled then. Thanks very much.

 

[cloa]

He really needs do his own assessment as while the suggested alloys are for chloromethane solution- in practice there will be only small areas with chloromethane and only temporarily in that condition so such high end alloys may not be reasonable.