RE: [MW:8072] RE: 8034] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

Mr. Babu

 

However, the query specifically stated it was bolted and if you note in my reply I recommended leaving loose or loosening the critical bolts if possible to allow for expansion.  I have assumed since it is bolted in place that there is no or minimal welding on the internals themselves thus SCC susceptibility should be unaffected by the heat treatment.

 

John

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Kathalingam Babu
Sent: Wednesday, November 03, 2010 10:25 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:8060] RE: 8034] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

 

John,

 

I would like to share some thing ,

 

Though , SS316L , will withstand against Sensitization,some extend on the sensitization temperature range during SR , there is more possibilities of formation of new residual stresses with existing residual stresses by welding.

 

These accumulated Residual stresses may lead to Stress Corrosion Cracking under corrosive medium

 

Regards,

 

K.Babu

Singapore

 

 

----- Original Message -----

From: John Henning

To: materials-welding@googlegroups.com

Sent: Wednesday, November 03, 2010 10:58 PM

Subject: [MW:8057] RE: 8034] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

 

Note: this response is directly to the question and applies only to referenced L-grade material

 

The effect on corrosion properties will be nil to minimal.

 

The use of the Low carbon (L) material minimizes any tendency towards chrome-carbide (M₂₃C₆).  For the L-grade austenitic stainless steels (3XXL) the carbon is kept below the solubility limit for carbon in solid solution.  Therefore there is little driving force to cause the formation of Cr-carbides that result in stress corrosion issues due to Cr depletion associated with elevated temperature exposures.  This is not to say that no Cr carbide may form along the grain boundaries, however if it does it will be discontinuous and will not cause corrosion problems.  Please refer to the attached generalized phase diagrams.

 

The effect on other material properties will be negligible.  The temperature is insignificant with respect to inducing structural changes.

 

There may be significant problems however with distortion of the members due to the difference in thermal expansion of austenitic alloys vs. carbon steel.  However, bear in mind that the size of the vessel  and length of the members play a major role in how much stress will be developed due to differential thermal expansion.  This may be compensated for by leaving critical connections loose enough to allow expansion and then retightening after PWHT.

 

Other than concerns with the latter point, there is no practical reason why the heat treatment could not be performed.

 

John

 

From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of asad azmi
Sent: Wednesday, November 03, 2010 1:44 AM
To: materials-welding@googlegroups.com
Subject: [MW:8034] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

 

Dear All,

 

Greetings.

 

Contractor is doing PWHT of the Carbon Steel Vessel along with  SS316L  INTERNALS ( BEAMS, CHANNELS) Bolted with the Vessel.  PWHT temperature is 600 DEG CELSIUS.

 

Pls  suggest me whether it is allowed. what will be the effect on mechanical proerties/corrosion ressiatnce  proerties of SS 316L becuase of the PWHT Temperature.

 

Thanks in advance for your valuable suggestions.

 

Regrads

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