Post Heating for Alloy Steel
senthil raja
I m Senthil working in L&T. I m presently in MRPL project,
Mangalore. In our client(EIL) specification it is given that post
heating shall be carried out for the alloy steels (Cr-Mo) where PWHT
cannot be carried out immediately.
I need to know what is the time limit within which PWHT shall be
carried out without post heating. What is the standard or code which
can be reffered for this.
Kindly share your experience sirs & friends,
regards,
Senthil Raja.
muthusrinivasan muthuselvam
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Jignesh Desai
sudharsan s
Devarajan Ramasamy
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GOSWAMI Pradip -THERMAL
Hi Senthil,
Post heating is termed as DHT(dehydrogenation heat treatment). This involves heating to a temperature (preferably above interpass temperature) immediately after welding to cause sufficient dissipation of hydrogen from the weld pool. This prevent any localized entrapment or build up of hydrogen pressure which may cause delayed or hydrogen induced cracking. EIL specification should mention the post heating temperature.
Otherwise based on the intended application you may follow API guidelines:-
· As per API Recommended Practice 934-E- Recommended Practice for Materials and Fabrication of 1¼Cr-½Mo Steel Pressure Vessels for Service above 825°F (441°C)- The DHT shall be performed at a minimum metal temperature of 570°F (300°C) for duration of one hour minimum.
· API RECOMMENDED PRACTICE 934-C-- Recommended Practice for Materials and Fabrication of 1 1/4Cr-1/2Mo Steel Heavy Wall Pressure Vessels for High Temperature, High Pressure Hydrogen Service-- The DHT shall be performed at a minimum metal temperature of 570°F (300°C) for duration of one hour minimum.
However the fabricator always have the option of extending the DHT time beyond API recommendations.
Thanks
Pradip Goswami,P.Eng.
Welding & Metallurgical Engineer/Specialist
Email-pgoswami@sympatico.ca,
From: material...@googlegroups.com
[mailto:material...@googlegroups.com] On Behalf Of Jignesh Desai
Sent: Wednesday, October 06, 2010 10:05 AM
To: material...@googlegroups.com
Subject: Re: [MW:7397] Post Heating for Alloy Steel
In ferritic steels, hydrogen embrittlement only occurs at temperatures close to the ambient temperature. Therefore, it is possible to avoid cracking in a susceptible microstructure by diffusing hydrogen from the welded area before it cools. After welding has been completed, the steel must not be allowed to cool to room temperature; instead, it should be immediately heated from the interpass temperature to the post heat temperature and held at this temperature for some minimum amount of time.
Also did you see UOP Spec 8-12-6, para 2.4(a) - Fabrication of piping?, where UOP asked for post heating of carbon steel? It may be carried out for some case of CS where thickness>50.0 mm). I am sure this spec. must be part of your project.
On Wed, Oct 6, 2010 at 11:47 AM, muthusrinivasan muthuselvam <msm...@gmail.com> wrote:
Mr.Senthil..
The main purpose of doing immediate PWHT without post heating is to avoid hydrogen induced cracking.. To my knowledge there is no code requirement or specification mentioning about the time after which you can do the PWHT.
But please note that delaying the PWHT after welding will improve the condition for hydrogen induced cold cracking. So the PWHT has to be carried out immediately after completion of welding.
best regards,
M.S.Muthu selvam.
On Tue, Oct 5, 2010 at 10:42 PM, senthil raja <senthilra...@gmail.com> wrote:
Hi,
I m Senthil working in L&T. I m presently in MRPL project, Mangalore. In our client(EIL) specification it is
given that post heating shall be carried out
for the alloy steels (Cr-Mo) where PWHT cannot
be carried out immediately.
I need to know what is the time limit within which PWHT shall be carried
out without post heating. What is the standard or code which
can be referred for this.
Kindly share your experience sirs & friends,
regards,
Senthil Raja.
--
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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.
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meant for educational purposes only, Users must take their own decisions w.r.t.
applicable code/standard/contract documents.
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muthusrinivasan muthuselvam
JASPAL SINGH
hydrogen induced cracking (HIC).
For HIC to occur; the following variables must be present. a sensitive
microstructure, a sufficient level of hydrogen, or a high level of
stress (e.g., as a result of highly constrained connections).
In Ferritic steels, hydrogen embrittlement only occurs at temperatures
cracking in a susceptible microstructure by diffusing hydrogen from
the welded area before it cools.
After welding has been completed, the steel must not be allowed to
cool to room temperature; instead, it should be immediately heated
this temperature for some minimum amount of time. Although various
code and service requirements can dictate a variety of temperatures
and hold times, 450°F(230°C) is a common post heating temperature to
be maintained for 1hour per inch (25 mm) of thickness. Post heating is
not necessary for most applications. The need for post heating assumes
a potential hydrogen cracking problem exists due to a sensitive base
metal microstructure, high levels of hydrogen, and/or high stresses.
Post heating, however, may be a code requirement. For example, ASME
Section III and the National Board Inspection Code (NBIC) both have
such provisions. The Section III requirement for P-No.1 materials
is450 to 550°F (230 to 290°C) for a minimum of 2 hours, while the NBIC
requirement is 500 to 550°F (260 to290°C) for a minimum of 2 hours.
Furthermore, post heating is often required for critical repairs, such
as those defined under the Fracture Control Plan (FCP) for Non
redundant Members of the AASHTO/AWS D1.5Bridge Welding Code. The FCP
provision is 450 to 600°F (230 to 315°C) for “not less than one hour
for each inch(25 mm) of weld thickness, or two hours, whichever is
less.”When it is essential that nothing go wrong, post heating can be
used as insurance against hydrogen cracking. However, when the causes
of hydrogen cracking are not present, post heating is not necessary,
and unjustifiable costs may result if it is done.
Jaspal Singh, CWI-AWS, CSWIP-3.1
Quality Assurance
Process Equipment Division
ISGEC, Yamuna Nagar, Haryana -135001
Phone: 911732307251
Ext: 251 Mb: +91 9996624244
On Oct 7, 12:36 pm, muthusrinivasan muthuselvam <msm...@gmail.com>
wrote:
> not close to ambient temperature.
>
> br,
> msms
>
> On Wed, Oct 6, 2010 at 7:35 PM, Jignesh Desai
>
>
> > In ferritic steels, hydrogen embrittlement only occurs at temperatures
> > close to the ambient temperature. Therefore, it is possible to avoid
> > cracking in a susceptible microstructure by diffusing hydrogen from the
> > welded area before it cools. After welding has been completed, the steel
> > must not be allowed to cool to room temperature; instead, it should be
> > temperature *and held at this temperature for some minimum amount of time.
> > Also did you see UOP Spec 8-12-6, para 2.4(a) - Fabrication of piping?,
> > where UOP asked for post heating of carbon steel? It may be carried out for
> > some case of CS where thickness>50.0 mm). I am sure this spec. must be part
> > of your project.
>
> > On Wed, Oct 6, 2010 at 11:47 AM, muthusrinivasan muthuselvam <
> > msm...@gmail.com> wrote:
>
> >> Mr.Senthil..
>
> >> The main purpose of doing immediate PWHT without post heating is to avoid
> >> hydrogen induced cracking.. To my knowledge there is no code requirement or
> >> specification mentioning about the time after which you can do the PWHT.
>
> >> But please note that delaying the PWHT after welding will improve the
> >> condition for hydrogen induced cold cracking. So the PWHT has to be carrried
> >> out immediately after completion of welding.
>
> >> best regards,
>
> >> M.S.Muthu selvam.
>
> >> On Tue, Oct 5, 2010 at 10:42 PM, senthil raja <
>
> - Show quoted text -
santosh bhandary
Can any one let me know that while preparing WPS, from where do we get the following values for a particular material:
|