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Technical Discussions
Shankar Arumugam
Other, NDE Engineer
India, Joined Oct 2013, 39

Shankar Arumugam

Other, NDE Engineer
India,
Joined Oct 2013
39
14:32 Feb-02-2016
PT/Wet MT - before PWHT- reg.

Dear Friends,
In High alloy steels (P91/T91) welds, after welding, post heating, bringing the weld to room temperature, before completion of PWHT, can we perform PT/Wet MT? Is there any effect to the weld due to the moisture/halogen content?

 
 Reply 
 
jon wallis
NDT Inspector, -
Netherlands, Joined Feb 2010, 626

jon wallis

NDT Inspector, -
Netherlands,
Joined Feb 2010
626
16:05 Feb-02-2016
Re: PT/Wet MT - before PWHT- reg.
In Reply to Shankar Arumugam at 14:32 Feb-02-2016 (Opening).

Due to the danger of cracking caused by the brittleness of P-91 prior to PWHT, MT is often performed on these welds and I've never heard of inspection materials being a problem. In fact P-91 is still a carbon steel so the problems of halogens as with stainless steels won't be an issue and the only problem moisture would cause is rusting but this is easily overcome.
I,m not a metallurgist but it seems common sense to me.

 
 Reply 
 
P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
23:04 Feb-02-2016
Re: PT/Wet MT - before PWHT- reg.
In Reply to Shankar Arumugam at 14:32 Feb-02-2016 (Opening).

Dear shankar,

You can very well do these tests without much problem but you have to ensure strictly the following conditions.

1. The job should be strictly at room temperature.

The welding stresses and the dissolved gasses are very high just after welding, particularly in P-91.

Even the carbon or low alloy steels exhibit very high residual stresses after welding due to shrinkage of the weld metal when cooled to room temperature . But this P-91 steel has higher alloy content
( Chromium content of about 9% with other minor alloys) and exhibits Martensitic micro structure just after welding. Because the formation of this micro structure is associated with sudden diffusionless transformation, the weld contains enormous residual stresses due to shrinkage compounded by violent micro structural transformation.

Over and above this any weld after welding has higher content of dissolved gasses including that of Hydrogen. Their solubility in the weld metal comes down with the temperature. They slowly diffuse out during PWHT.

So just after welding and before PWHT the P-91 welding is a potential site ready to crack ( if cracks have not already come) at the slightest mishandling. It should be handled like glass.

Under the circumstances even if the weld is 30 to 70 degrees Celsius above the room temperature the cooling stresses caused by application of the PT/MT materials may become the reason for cracking.

After PWHT the micro structure transforms to Tempered Martensitic phase with reduced residual stresses and dissolved gas content, then the P-91 weds becomes much safer for handling.

2. No mechanical work like grinding, chipping etc should be done for surface preparation. Only light brushing by brushes with brass bristles may be done.

3. After the testing, residual chemicals/solvents should be thoroughly cleaned lest they may interact with fragile surface conditions to create problems.(before PWHT)

4. In general the PWHT should be done at the earliest for P-91 welds as they are highly susceptible for cracking in as welded condition, even without conducting any NDT.

With Best Wishes,

P V SASTRY

1
 
 Reply 
 
Shankar Arumugam
Other, NDE Engineer
India, Joined Oct 2013, 39

Shankar Arumugam

Other, NDE Engineer
India,
Joined Oct 2013
39
07:08 Feb-03-2016
Re: PT/Wet MT - before PWHT- reg.
In Reply to P V SASTRY at 23:04 Feb-02-2016 .

Thank you very much for your valuable reply and now I came to the conclusion that, at room temperature we can perform PT/Wet MT in P91/T91, before PWHT.

 
 Reply 
 

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