[MW:18218] RE: 18216] Heat treatment for TP 321 steels

Hi Jose,

Stabilization anneal HT is typically recommended for refinery application for 300 series austenitic S.S and other austenitic alloys to mitigate Polythionic acid SCC (PTASCC).

This damage mechanism is typically associated with refining high "S" crude and occurs typically during the shutdown cycle. Polythionic acid (it's in the family of Sulfurous/Sulfuric Acids) gets formed by reaction of oxygen and water with sulfide corrosion products (i.e., metal sulfides) or with other oxidizable sulfur species (e.g., sulfur, hydrogen sulfide [H2S]), during the shut down cycle.

The typical stabilization anneal cycle recommended by NACE SP 170-2012(formerly RP170-2004) is:-

•   843 to 900 °C (1,550 to 1,650 °F) for 2 to 4 hours to preferentially allow the precipitation of titanium or niobium carbides. Cr stays in solution around these temperatures which ensures the corrosion resistance of 321 grade S.S.

 

FYI the other document to know about various effects of PTA SCC  and engineering mitigation techniques is API -RP-2011 or earlier versions. See below the extracts of API-RP 571.

Following stabilization anneal, ASTM A 262 Practice C is advisable (when asked  by the  client).

 

In order to pass the stabilization anneal HT on PQR , BOTH base metals, welding  consumables should  be procured stabilization HT and above ASTM test if asked for.

 

Thanks.

Pradip Goswami, P.Eng,IWE

Welding & Metallurgical Specialist

Ontario, Canada

pgoswami@quickclic.net

pgoswami@sympatico.ca

 

• A thermal stabilization heat treatment at 1650 DegF (899 Deg C) may be applied to chemically stabilized austenitic stainless steel welds after all welding is complete in an attempt to reduce sensitization and PTA susceptibility. This heat treatment is difficult to apply in the field.
• Susceptibility to PASCC can be determined by laboratory corrosion testing according to ASTM A262 Practice C. A sensitizing heat treatment is often applied to L and/or chemically stabilized grades prior to testing.

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From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of José Luís Ferreira
Sent: Thursday, July 18, 2013 7:59 AM
To: materials-welding@googlegroups.com
Subject: [MW:18216] Heat treatment for TP 321 steels

Dear all,

The specification of my client requires to be carried stabilization heat treatment in WPS qualification for material TP 321, but does not specify parameters for this treatment, says it should be agreed in advance. Usually the parameters which are adopted?

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