Duplex Stainless Steel Pump casing

[Hari Srinivasa Murthy]

Dear Friends,

 

Recently in one of our water injection plants, we experience  leak from a pump casing.The leak was due to a suspected minor pinhole. Pump casing is of Duplex Stainless Steel (ASTM A 891). Casing thickness is about 100 mm. Pump working pressure is 5000 PSI.

We have opened the pump  performed DP on the casing internally and externally to identify the path of the leak and causes of leak. We have identified 4 suspected spots from inside the casing, which could lead to  the leak. We have taken Radiography (using Ir192- 14.2 ci) of the casting  with high exposure times but could not get any clear result. We have also used available low frequency VSY UT probe to detect the cause of the leak. This probe could provide us details of casting defect  up to 15-16 mm only. We could not decide the leak path withis information.

With the above background, I would like to request our forum specialists to suggest me  NDT methods to identify the leak path throughout the casting thickness and to share related experiences if any in your facilities.

 

 

Regards

Srinivasa Murthy Hari

 

[hpi001]

Dear Sir,

Unfortunately it's not easy to perform Non Destructive Examination on
castings especially when you want to find some small pinholes in 100
mm thick Duplex Stainless Steels. I'm working for a foundry where we
cast such pump casings as well and I must say the only reliable way of
NDE is radiographic examinations, but than only for larger type of
failures. We always perform 100% Dye Penetrant examination on the both
internal and external surfaces of pressure containing parts as casings
in order to find any pinholes. If we find any pinhole we remove the
failure as far as possible by way of gouging and perform repair
welding. I have to say that this involves always materials in the as
casted condition so we easily can execute such repairs because this
will be followed by final solution heat treatment in order to solve
any unwanted microstructural . We often try to find indications with
Ultrasonic Examination, we even tried Phased Array but than as we
assume the casting is without any identification because of the UT
examination often not acceptable indication will be found during
machining.
In my opinion there are no examination methods to identify the path of
such pinhole through the wall thickness.

If, and I assume this will be the case, the casing is in the final
condition I only can propose to remove the indication carefully up to
a depth which can be welded without getting any problems with final
dimensions due to shrinkage. I don't think it will be technical
possible to remove the full indication but when you can repair the
location afdoende for about 15 mm depth from both surfaces you won't
have a problem with the pressure inside the casing.
If you allow repair welding be sure that the company who's performing
such has a PQR for repair welding without any heat treatment
afterwards. Because when you need to perform such heat treatment you
can get problems when assembling the pump afterwards because of
possible distortion.

Best Regards,

Herman Pieper

[Hari Srinivasa Murthy]

Dear Mr.Herman Pieper ,

 

Thanks for your detailed reply. Initially we also thought of repairing it upto 15 mm thk. But our previous experience in the company on DSS shows  internal creater cracks inside castings though they appear to be pinholes from outside. Cobalt RT source is not available in our place for RT of the defect location.One of my colleague suggested me to carryout Phased Array Technique. 

 

Can you please write me your experience with phased array technique on such castings.

 

Regards

 

Srinivasa Murthy Hari

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[rajagopal kannan]

Dear Murthy,

try a post emulsification PT, if accessible, so that you can locate the pinholes on both sides precisely. but there are least chances for any NDT to detect a leak path.

Thanks,

K.Rajagopal

--

[AGUSTIN JIMENEZ]

Dear Murthy.

I Recomended 2 procedure:

1.- Use Fluorecent PT. cover all pump and created dark space.

or

2.- My experience practice, put gasoil,  on outside pump and check with

black light lamp or normal lamp inside pump.

 

and say me if you can will do it.

 

best regards

Agustin Jimenez 

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De: rajagopal kannan <rajagopa...@gmail.com>
Para: material...@googlegroups.com
Enviado: dom, marzo 7, 2010 11:35:15 PM
Asunto: Re: [MW:4482] Duplex Stainless Steel Pump casing

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[hpi001]

Dear Mr. Hari Srinivasa Murthy,

We did some test on DSS material with Phased Array technique because
of problems with ordinary UT examinations. The NDE company told us
that they will get a better view when using Phased Array but at the
end they couldn't get a clear view. Probably the cause for this are
the different wall thickness in such pump casing which will cause
different cooling rates when perform forged cooling after solution
heat treatment. Due to this differences you also will get different
grain sizes afterwards and those transition areas to different grain
size also causes reflections during ordinary and Phased Array UT
examination. This also can be the problem with heavy wall thicknesses,
the core of the material will cool down much slower as the material
near the surfaces. When having material with similar properties
through the thickness (mostly not the case for catings) Phased Array
will give you a better view as ordinary UT but when we looking at
small pinholes you will also have the problem that it isn't a flat
indication and therefore UT waves will spread without a clear view of
the indication of interest.
You may give it a try but I don't think you will get a clear view of
the exact location of the pinhole with Phased Array, we performed some
tests on pump casing in materials 1.4470 / 1.4469, depending on the
type A891 could be the EN 10213 equivalent for your material. During
this we sometimes did found some indication but this was never a
pinhole, detected indications were mostly related to shrinkage and/or
slag inclusions and general have more volumetric dimensions.

When you decide to repair the casing always perform GTAW process for
the first layer and execute visual examination after the first layer
in order to ensure that there is no crack present. Incase of doubts
always perform PT examination before welding a second layer. Once you
have sound material you may go for an other welding process such as
GMAW in order to reduce the heat imput.

I hope this helps you out to decide how to go on.

Best Regards,

Herman Pieper