Duplex Pipe A790 UNS S31803 in High and Low Temp Service 3

[Angsi]

Our process engineers for some unusual reason requested the piping department to consider increasing and lowering the design temperatures in a couple of duplex piping classes.

These materials are now expected to serve design temperatures of 156 C and -100 C.

Piping Code used is B31.3
Location: Offshore marine environment
Application: High CO2 hydrocarbon gas

First Question
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Duplex pipes are normally limited to a maximum of 100 C if they are uncoated. I understand with the appropriate coating for the temperature range, duplex pipes design/operating can be taken up to 200 C. Is this correct?

Second Question
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The minimum design temperature limit for duplex pipes as per B31.3 is -60 deg C. With impact testing, one can expect the temperatured be lowered a bit, maybe upto -85 C. Has anyone here has the experience of using duplex pipes in such extreme low temperature condition. Will the material be able to withstand the charpy impact testing?

Thanks in advance.

 

[EdStainless]

The exposed temp limit has to do with pitting and CSCC issues. If it is over 100C then water on the surface will evaporate leaving all of the salts and creating very highly concentrated solutions which will attack the alloy.

If they are properly protected these alloys will work up to 315C, provided internall corrosion isn't an issue.

You will not be able to go too low in temp. These alloys have a DBT, there is no getting around it.

= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.

http://www.trenttube.com/Trent/tech_form.htm

 

[bruv]

I have some thoughts for you:

1) What prior experience have your process engineers in using duplex at higher/lower temps? Have they considered carrying out corrosion testing (with or without coatings) at these temperatures? Are tesile strengths within design limits at 200C?

2) Get a bunch of Charpy tests done at all temperatures from RT down to below the minimum service temp. This will generate a transition curve, showing you where the brittle/ductile transition takes place. Work with potential suppliers on this, as they may have the knowledge you need.

3) If the pipework is supposed to operate at these temps, what about the valves? Will these operate in the same conditions. The lowest temperature we have been asked for charpys on duplex castings is -50C.

Bruv

 

[SJones]

In our previous correspondence, it was indicated that Shell DEPs are applied in your work. Assuming similar in this instance, you will note that several Shell specifications will limit the application of duplex, and superduplex, to -50 - +120 deg C. Your first hurdle will, therefore, be to provide a suitable basis for the deviation. As for protection of duplex, superduplex is considered capable of being uncoated up to 120 deg C, after that thermal spray aluminium should be the only coating entertained on pipe of DN50 and above. Below DN50 - change the material to a higher alloy. Irrespective of design temperatures, Shell will require Charpy testing at -50 deg C.

Hope this helps.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[Angsi]

Hi Steve, The operating company that I am working for is not Shell or nearly as large. However, I do at times refer to Shell DEPs. My company hasn't standard engineering specifications for engineering. We try to standardize engineering details as we progress from one project to another(!!!?).

W.r.t duplex pipes temperature limitations, yes, I am aware of Shell's piping classes and I did check them earlier.

I may now have to question process engineer's blowdown calcs and see if there are able to control the temperature drop.

Thanks.

 

[SJones]

Ok Angsi. It's clearer now about your specification approach. Always a good idea to challenge the process engineers as they may be being extremely conservative (on some instances in our current project we have chiselled them up from -80 deg C to -50 deg C that at least puts us back in the realms of carbon steel). Given this scenario, you will be able to work the allowable limits of B31.3 (that are not allowed by Shell) to gain some leeway in temperatures.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[TomEun]

1. Maximum Temperature Limitation of 2205 DSS

1.1 ASME B31.3, Table A-1
; 600 deg.F

1.2 ASME Sec.VIII, Div.1 and Sec.II, Part D, Table 1A
; 600 deg.F

2. Minimum Temperature Limitation of 2205 DSS

2.1 ASME B31.3,
[Table 323.2.2]
; Impact test for welds and HAZ is required when MDMT is colder than -20 deg.F.
[Table A-1]
; -60 deg.F

2.2 ASME Sec.VIII, Div.1, UHA-51(d)(3)
Impact test @ the MDMT is required for the DSS which is thicker than 3/8" when MDMT is colder than -20 deg.F.

---> If you do the impact test for 2205 DSS, you may be able to get the DBTT,-40 to -60 deg.F.

Hope this helps,

Thomas Eun

 

[rorschach]

From my previous experience with super duplexes (Foroni 918, SAF2507) I would also point out that many alloys in this class experience a pronounced loss of strength at high temps. If memory serves, around 150C, Foroni 918 has gone from 85ksi yeild to around 60. depending on the system design, that loss of strength may be an issue. Marco Deuterio who is the local Foroni Rep here in Houston can give you more specifics for 918 if you are interested.