Duplex Pricing 5

[NPKresults]

Hello, I have been looking into substituting duplex stainless for our 300 Series applications. From what I have read it seems like duplex has similar if not better overall corrosion resistance than 300 Series and I was hoping that it would be cheaper due to its lower nickel content. Particularly I was looking at 2205 and 2003 to sub for 316 and 304. Unfortunately many of our suppliers do not carry duplex and when I found one who did it turned out to be more expensive than the 300 (in decreasing order of price: 2205, 316, 2003, 304). I was hoping for any thoughts on:

-Are 2205 and 2003 fully substitutional for 304 and 316?
-Are these duplex steels ever cheaper than their 300 Series competetors?

The quote I recieved was for orders of 20,000 lbs. and I am located in the US Mid-Atlantic region. I understand that Duplex is stiffer and requires variations in welding and machining procedure, my main concern would be with the corrosion resistant properties. I realize the question is very generalized, any and all thoughts are greatly appreciated.

Thanks,

Danny B

 

[TVP]

Danny,

There is a group (different from a forum) here at Eng-Tips called stainless steel for engineers that has a great deal of information on converting from austenitic to duplex grades. Since the duplex grades are considerably stronger and often more corrosion resistant than 304/316, the design can be changed to feature thinner sections and therefore lower cost. mcguire and EdStainless are regular contributors on this subject, so you may want to start with a keyword search usign their handless together with duplex, 2205, 2101, 2003, etc.

 

[EdStainless]

Well, I can answer here as well as in the other forum.
There are some general cautions about duplex alloys.

-They are stronger than austenitic grades, so use thinner material where you can and be prepared for more force needed to cut and form.
-They cannot be used above 600F.
-They have a ductile-brittle transition temp. Be careful if you are going to use them below -40.
-They all have better chloride stress corrosion cracking resistance than any austenitic stainless grade.

A rough order of increasing resistance to chloride pitting (crevice) corrosion: 201, 304, LDX2101, 316, AL2003, 2205.
In rough terms you can think of LDX 2101 as an upgrade from 304 and AL2003 as an upgrade from 316. 2205 has significantly higher corrosion resistance.

The price that you pay will be heavily dependent on the volumes. The order that you have is correct. From lowest to highest: 201, LDX2101, 304, AL2003, 316, 2205.
In volume for sheet or plate 316L and 2205 are the same price today once you include all surcharges. Here some rough numbers for volume purchase of flat products:
201-$2.10/lb, LDX2101-$2.20/lb, 304L-$3.00/lb, AL2003-$3.25/lb, 306L-$4.40/lb, 2205-$4.45/lb.

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[moltenmetal]

A couple of things to add to EdStainless's excellent list:

- right now, availability in small-bore piping and fittings is vastly inferior for any of the duplex grades relative to 304/316. Regardless what the alloy surcharges say, you may pay a premium if your principal use for the material is piping. As more people make the substitution, perhaps this will change.

- to maintain the duplex structure and its corrosion resistance, welding must be done VERY carefully. Procedures need to be qualified with metallurgical tests for ferrite content. Welds need to be done "cold" and hence take longer to do.

- yes, you can use thinner sections due to the higher strength, but if you're already at sch 10S no benefit will be realized. Even in the more common grades, sch5S is usually sold at a premium to sch10S

 

[davefitz]

We have about 1 yr experience in using 2205 in FGD scrubber service, and can add:

improved corrosion resistance is not the same as being immune to corrosion. In particular , crevice corrosion is a major issue. Damage is being repaired by weld overlay. later jobs will likely add some type of surface sealing at lcoations susceptible to the layout of stagnant corrosive liquids to forestall the crevice corrosion issue.

Google searches on the topic of corrosion of 2205 yield the following potential causes:

a) critical corrosion temp of 122 F is at or below the design operating temp of a FGD scurbber

b)corrosion reisistance is related to sigma phase formed in intial cooling during fabrication or welding.

c) corrosion can be accelerated by impressed currents or galvanic corrosion effects.

 

[EdStainless]

I'll add one more thought. If you buy any duplex, any alloy, any product form, you should require A923 as part of your spec. There should be no intermetallics in the material. Period.

Dave, How about a redesign to allow surfaces to drain and not collect moisture?
a) CCCT has noting to do with actual service temperatures. These tests are done in synthetic environments and are used to rank alloys.
b) There will be a small amount of IM in the HAZ of welds. There should be none anywhere else. The lean grades are at least an order of magnitude more resistant to this than 2205.
c) ...as with all metals.


= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[davefitz]

ed,
Thanks for the information on A923. The corrosion is primarily at flange faces and dead zones near manways, access hatches, etc. Drainage is not the fix in those cases. weld overlay, epoxy, flake glass, rtd, any thing to seal the surface at these dead zones will be tried.

I understand that weld overlay leads to a nitrogen denuded zone that may have accelerated corrosion.