Tuesday, September 7, 2010

[MW:6911] RE: 6879] Re: Duplex and Super Duplex Stainless Steel

Herman,

Just a quick note. S-numbers have been deleted and where appropriate converted to P-numbers.

See 2010 Section IX, Introduction, Welding and Brazing Data - page xxviii, 2nd column, 3rd paragraph: "In the 2009 Addenda, S-Numberbase materials listed in the QW/QB-422 table were reassigned as P-Numbers and S-Number listings and references were deleted."

It is my understanding that the original intent was to permit extended welding qualification for materials approved for use by B31 committees but not included in Section II (and therefore not permitted by Sc I or Sc VIII). Section IX determined that this had nothing to do with weldability and the user should be aware of what/where the material was permitted to be used.

John

-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of hpi001
Sent: Sunday, September 05, 2010 5:05 PM
To: Materials & Welding
Subject: [MW:6879] Re: Duplex and Super Duplex Stainless Steel

Dear Limesh,

The difference between Duplex and Super Duplex is the so called PREN
values (Pitting Resistance Equivalent Number) which for Super Duplex
should be >40. So this material has better properties against pitting
corrosion compared to standard Duplex Stainless Steel. PREN is also
called PI (Pitting Index) in some specifications.
You can calculate this value by way of the following formula: PREN =
%Cr + (%Mo x 3.3) + (%N x 16) , so to get this value above 40
manufacturers will add some extra Cr, Mo and N compared to standard
Duplex.

The P.no. for most of the Duplex and Super Duplex materials is P.no.
10H, Group No. 1 but some materials (f.e. UNS 32205 (2205)) has no
P.no. but a S. no. (see QW 422 of ASME section IX).

The reason that your impact test fails often is related to the
presence of inter-metallic inclusions such as Sigma Phase in the micro-
structure, which is caused by not controlling the heat input during
welding. Inter-pass temperature should not exceed 175 °C in order to
prevent such unwanted inclusions. An other possible cause can be
cooling down slowly from 850 °C to 350 °C which can cause brittle
structure as well.

Hopes this helps you out.

Best Regards,

Herman Pieper

On 5 sep, 18:29, limesh M <limes...@gmail.com> wrote:
> Dear All,
>
> What is the difference between Duplex and super duplex stainless
> steel?
>
> What is the P. No for duplex and super duplex stainless steel?
>
> One of our duplex stainless steel PQR failed in impact test.What would
> be the reason?
>
> Thanks and Regards,
>
> Limesh

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