Duplex stainless steel - Dual certified 1

[sreekrishnan]

ASTM A790 S31803 / S32205 dual certified.

Which material proportion they will change to maintain the dual certificate?

From ASTM standard, i could see changes only in Cr (less diff) and N.

 

[EdStainless]

They are meeting the more restrictive chemistry (Cr, Mo and N are all tighter) and mechanical properties (95/70 vs 90/65) of S32205, and since these lie completely withing the ranges for S31803 it naturally meets that also.
You want the S32205 composition, it is more stable and has better corrosion resistance, but you need S31803 listed since some Code application still only refer this UNS.

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P.E. Metallurgy, Plymouth Tube

 

[sreekrishnan]

Many a thanks for your quick reply. In that case, we could directly go for S32205 (since it has better corrosion resistance) instead of mentioning both S31803/S32205?

 

[MickMc]

An excerpt from US Supplier website which compliments EdStainless reply.



The term "dual certification" is most commonly used to refer to the practice of certifying a material as meeting the requirements of a specification(s) as two different alloys.

The most common example of this type of "dual" certification is that of 304 and 304L (or 316 and 316L). Material melted to the lower carbon range and processed to maintain the minimum properties for the straight grade will qualify as both "L" grade and regular grade. This dual certification has been a standard practice for years since AOD refinement essentially eliminated the cost differential between regular and low carbon versions. Into the mid-70’s there was a significant premium charge (as much as 10%) for low carbon 304 and 316. It should be noted that dual certifying of this type is not permitted when it encroaches on the principle of grade substitution. For example, Type 321 stainless could meet the chemical and mechanical property requirements of 304, but since it also has the intentional addition of another element (titanium), it cannot be certified as 304.


It is also common to see Alloy 2205 dual certified as both UNS S31803 and UNS S32205. The original broad chemistry limits for S31803 permitted a composition that could result in poor mechanical and/or corrosion properties. The S32205 chemistry limits fall within the original ranges, but are restricted to ensure better properties. The S32205 material also has a slightly higher minimum tensile. Dual certification was necessary, in part, because until recently only the S31803 alloy was included in the ASME B&PV Code.

 

[pradipgoswami]

You may choose 32205 or dual certified 32025/31803 material, provided it meets all the design code and specification requirements. Both materials are classified as P No-10H, Gr-1 in ASME Sec-IX and accepted in 2013 onward version of ASME Codes(both Sec-IX & Sec II,Pt-D). Note matching welding consumables for both materials are ER-2209 or E-2209. Hence re-qualification of welding procedure may not be necessary, if-not mandated by clients for specific applications.You may have to review the specific requirements of specific Corrosion Test, such as G-48A Pitting or SCC Test or IGC Test as per ASTM A-262.

If the vendor classifies material as dual certified grades then the ASME Code rationales should be clearly mentioned(not mandatory but explanation would help).

[highlight #FCE94F]32205 had been the baseline of Duplex stainless steel, originally developed by Sandvik/Avesta,in 1980's and predominately had been the better grade and European version of UNS 31803[/highlight]. UNS 31803 is predominantly an North American Version, introduced later and incorporated in ASME design codes much earlier. UNS S32205 material properties for use in Section VIII, Divisions 1 and 2, were incorporated only recently in in 2013 version of Sec-II, Part -D.

[highlight #8AE234]If there is a choice, then 32205 would be the better pick and the chemistry conforming to this grade would provide better reliability.[/highlight]

Please see the link below and the attachment for more explanations.

Thanks.

http://www.rolledalloys.com/technical-resources/blog/dual-certification

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario,Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299
All provided answer are personal opinions or personal judgements only. It's not connected with any employers by any means.