effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

[asad azmi]

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

[Karthik]

Hi, It is not recommended unless otherwise in case of PWHT required on cladding vessels.you can re assemble the internals after PWHT since it is a bolted connection. Thanks & Regards, (Karthik) Karthikeyan.S QA/QC Manager Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8 (Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282 --- On Wed, 11/3/10, asad azmi <azmias...@gmail.com> wrote:

-- To post to this group, send email to material...@googlegroups.com To unsubscribe from this group, send email to materials-weld...@googlegroups.com For more options, visit this group's bolg at http://materials-welding.blogspot.com/ The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.

[Karthik]

hi, If you PWHT with Austenitic SS (SS316) internal sensitation happened at 450 to 600 degrees which will reduce the corrosion resistance of SS316(chromium becomes chromium carbide). But in your case it is SS316L ,for this it may PWHT since 'L" grade has stabilising elements like Ti,Cb,Nb which will help to reduce the sensitation. So if you are not ready to dismantle the internal for PWHT,you may go with SS316L internal for PWHT.

Thanks & Regards, (Karthik) Karthikeyan.S QA/QC Manager Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8 (Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282 --- On Wed, 11/3/10, asad azmi <azmias...@gmail.com> wrote:

From: asad azmi <azmias...@gmail.com> Subject: [MW:8034] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L To: material...@googlegroups.com Date: Wednesday, November 3, 2010, 1:44 PM

[Kathalingam Babu]

Hi

 

SS 316L doesn't have any Stabilizing elements. Since the lower percentage of carbon , the tendency of Cr Carbide formation is less.

 

Sensitation temperature range for the SS316 is typically in the range of 600~850 deg. cel.

 

If you want to do PWHT, you may do less than 575 deg. cel. and increase the soaking time accordingly.

 

In my opinion, I'll not recommend for PWHT with internals.

 

Regards,

 

K.Babu

Singapore

[Bathula Raghuram (Mumbai - PIPING)]

There could also be a possibility of distortion

[Bisso, Giuseppe]

PWHT  on austenitic stainless steels  (like 316,304) is rarely applied ad “stress relieving”.

Sometime applied in medium-small size pressure components ( welded).

The temperature are in the range 205-480 °C max, normally carried out ad 300 °C but only with the scope to get an effective stress-relieving.

Heat treatment carried out in dedicated & ventilated  (electric furnaces), in order to avoid or control possible distortion/warpage.

 

 Joseph B  ,

welding & material eng.

 

---

Da: material...@googlegroups.com [mailto:material...@googlegroups.com] Per conto di Karthik
Inviato: mercoledì 3 novembre 2010 8.45
A: material...@googlegroups.com
Oggetto: Re: additional detail[MW:8038] effect of PWHT Temperature at 600 DEG CELSISIUS ON SS 316L

---

This e-mail contains privileged and confidential information intended for the use of the addressees named above. If you are not the intended recipient of this e-mail, you are hereby notified that you must not disseminate, copy or take any action in respect of any information contained in it. If you have received this e-mail in error, please notify the sender immediately by e-mail and immediately destroy this e-mail and its attachments.

[Karthik]

hI, I agree with Mr.Babu.But as far as i know Sensitation Temp.range for SS316L is 450 to 600 degrees. My doubt is If Sensitation Temp.range for SS316L is of 600 to 850 means,In case of doing Stress reliving(some times after forming needed) around 850 degrees will it get sensitised?

Thanks & Regards, (Karthik) Karthikeyan.S QA/QC Manager Getabec Energy Co.,Ltd. 379,Moo6,Soi8,Nikhomphatana, Rayong-21180, Thailand. Phone: 0066 38 897035-8 (Off) Fax: 0066 38 897034 Hand Phone: 0066 892512282

--- On Wed, 11/3/10, Kathalingam Babu <kathalin...@ppl.com.sg> wrote:

[Kathalingam Babu]

Hi Karthik

 

Yes there is more chances for the sensitation , if you SR at the sensitation temp. range after forming. 

 

Cold forming of SS316L  is generally SR Iis not required, as it is having good ductility and formability.

 

Also we need to have the Capcity of Equipment is higher than what we using for the SS304.

 

Upto 8 mm thk, very well formed , with generally available equipments.

 

Regards

 

K.Babu

Singapore

[Kathalingam Babu]

Hi

 

Apologies for the incorrect spelling of "Sensitization"

 

Regards

[Shashank Vagal]

Hi, PWHT (for SR) holding period at the appropriate temp should be as low as possible so that Cr-C does not get much chance to precipitate out. Please refer to a metallurgist for any good solution annealing procedure. Though its purpose is different, the functionality is almost the same. As per my past experience, the job is held at a temp outside the sensitization range till temp gets stabilized, then quickly quenched in a few seconds to below 300 deg C by immersing it in to an iced brine solution (if at 800 deg C or so) or allowed to cool in a ventilated furnace (if below 300 deg C). The PWHT itself and correct temp selection and  distortion minimization measures are the critical issues. The best advice with SS is to avoid PWHT. Since your internals are bolted, why not dismantle them and do PWHT of the remaining CS components? Rgds, Shashank Vagal

[John Henning]

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

 

Dear All,

--

[Kathalingam Babu]

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

[Mayank .]

Asad

Agree 100% with John . I was involved in the fabrication of second
largest Vacuum Distillation Column / VD Column here in India (as of
2003 ).

regarding the PWHT {correct me if I am wrong }it is not SR on the
whole vessel. PWHT is to be done on the BAND of 300 mm near all the
HIGH THK Weld areas that are classified as PWHT required , and that
is completely ok . {our designer was GOOD , he envisaged the problem
during design & provided all the cleats inside the Vessel either above
/ below the Weld Seams by 200-350 mm either side that made our job
Easy to PWHT the Weld } but make sure that all the bolting is loose at
one end as there is a good thermal gradient in CS & SS that works
opposite to all our interests (will not be in the cladded area as such
it is with the outer shell Vs SS Internals - Thermal Expansion ) .
outer shell starts to bulge as CS and the loose end may not rest if
the cleat tolerances are on the smaller side. I have seen a 150 mm
extension on this particular bottom shell on all directions {this is
during initial fabrication so no problem of falling internals } during
PWHT & retract most of the length after cooling

If internals are packings then try to remove the peripheral packings .

If the internals are trays then

if chimney trays are already welded you may consider a CUT in between
& reweld if the whole equipment is being HT (as SS internals {assumed
SS internals} will not expand with reference to the "bulge" during the
HT of the CS equipment ).
Bolting bar can be left loose at one End . & all other trays are just
bolted to the Trays so I guess your contractor has to do a double work
as internals may be in a heap in the bottom of the shell after HT.

it will be the same for Crude Distillation Column too , for that
matter any Column / Vessel with internals.

L grade esp 316L is chosen as there is no enough carbon left for
sensitisation (formation of chromium carbides) ...

hope this helps

regards

Mayank

[Prabhakar Raj]

Hi,

Grade 316L, the low carbon version of 316 is immune from
sensitisation (grain boundary carbide precipitation).

So, there will be no problem if you do PWHT at temperature 600 DEG
CELSIUS for SS316L.

Regrads

Prabhakar,
BV

[Prabhakar Raj]

Hi,

For Sensitisation to occur in SS, carbon is required.

Grade 316L, the low carbon version of 316 is immune from
sensitisation (grain boundary carbide precipitation).

So, there will be no problem if you do PWHT at temperature 600 DEG
CELSIUS for SS316L.

Regrads

Prabhakar,
BV

[John Henning]

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: material...@googlegroups.com [mailto:material...@googlegroups.com] On Behalf Of Kathalingam Babu

Sent: Wednesday, November 03, 2010 10:25 PM
To: material...@googlegroups.com