Repairs after hydrotesting

Date 07-31-2008 00:07

Hello gentlemen,
Need a little bit of assistance please.
We have purchased some large pressure vessels that were fabricated to ASME VIII Div 1 and they had previously been signed off by the notified body in the country of manufacture.
As part of the refractory process a groove was ground in the main circ weld at the carbon steel/titanium interface. Unfortunately the contractor ground too deep and we have had to reweld the areas. This welding was conducted using the temper bead process which negated the requirement for PWHT. Following rebuild these areas were radiographed and MT tested and numerous transverse cracks were discovered by the MT (Both in the original metal and the rewelded areas.)
We are now removing these cracks and rewelding.
I cannot find anything in ASME VIII that definitively states that a hydrotest must be performed after repairs.
Does anybody know if this is a requirement ?
It is our understanding that a hydrotest must be performed after fabrication is completed but the contractor is stating that fabrication was completed when the vessels were signed off but it is now not required.
Any help would be greatly appreciated,
Regards,
Shane

By fbrieden (***)

Date 07-31-2008 03:45

Is this an "R" stamp procedure?

By Shane Feder (****)

Date 07-31-2008 04:42

No, we are based in New Caledonia and there is no requirement (to the best of my knowledge) for the vessel to be stamped.
Regards,
Shane

By new tito (***)

Date 07-31-2008 13:16

Shane,
This sounds like it should fall under NBIC and the "R" stamp.

In any case, with the extent of the repair, I would hydro again.

By Mikeqc1 (****)

Date 07-31-2008 17:49

shane if you want to reasearch this further try this forum......
http://www.onetb.com/forum.htm

By G.S.Crisi (****)

Date 08-05-2008 00:01

Let's put our horse sense to work.
When the vessel was originally signed off (how I like those King's English expressions!) it was supposed to be OK.
Then, before installing the refractories, the contractor ground a groove which happened to be too deep and it had to be repaired by welding. Who warrants me that the new welding will stand the vessel operating pressure? If I were the client, or the inspector, I'd require a new hydro test.
But then, numerous cracks were discovered, not only in the rewelded area but also in the original metal, which demonstrates that whoever signed the vessel off was, to say the least, negligent or ignorant. Now you are repairing the cracks by welding.
Are you sure you've identified all of the existing cracks? Who warrants me that cracks are not spread all over the vessel?
If I were the client, or the inspector, apart form the hydro test I'd also require also a complete search of cracks all over the vessel weldings.
Giovanni S. Crisi
Sao Paulo - Brazil

By Shane Feder (****)

Date 08-05-2008 00:59

Giovanni,
Thank you for your response.
It is actually quite a long story but will try to abbreviate.
My employer decided that there was no need for us (CWIs) to perform audits on our contractors (this applied to numerous items fabricated all over the world) and that the inspections would be performed by a well known third party inspection company in their respective countries of origin. This turned out to be a major mistake as numerous items arrived on site with problems that were never identified by our third party.
The major circumferential welds were only RTed as per ASME VIII Div 1 and were found to be acceptable and the results were accepted by a well known notified body. As such they were "signed off" and shipped to our site. All of the transverse and longitudinal cracks have been discovered on site by the MT method which was never performed in the factory.
A piece was cut out of the butt weld and sent to a laboratory for analysis. EDS (Energy Dispersive Spectroposcy), AES (Atomic Emission Spectrometer), SEM (Scanning Electron Microscope) and Hardness tests were performed and numerous anomolies were found but probably the most critical was the high titanium content of the weld metal.
We are still investigating how this titanium got into the weld metal. (Whether from weld dilution of the adjacent titanium overlay or possibly "smeared" into the groove by the grinding process.)
I have located the required information - UCS 56 (f) (6) " The vessel shall be hydrostatically tested after making the welded repair."
Thanks everyone for your responses,
Regards,
Shane

By Noel Tan (**)

Date 08-05-2008 05:46

I do agreed with Giovanni, i really have doubts on the testings and inspections if you are able to find many cracks
after all required PWHT, NDT and hydrostatic test have been performed and found complied.

IF you work under your employer (the end user of the PV), it should not be your responsibility to instruct them how to solve this probelm.
your company paid the contractor as well as the well known third party, they should be responsible to investigate and to proposed what
they need to do in order to satisfy the code requirements and your company.

UCS 56 (f)(6) is one of the requirement when you intended to aviod the PWHT on the repair welding which done after the required PWHT
but before hydrostatic test under the normal condition. your case is abit different as there is a doubt on the full integrity and soundness
of your PV. Anyway, hydrostatic test should be the minimum without considering other factors (Testing and PWHT).

Regards,
Noel

By TimGary (****)

Date 08-07-2008 13:04

Are the cracks in the original welds from your supplier, or do they originate from your subsequent material thickness repair?
If there are defects in the vessel as supplied, you should reject the vessel and send it back to the supplier. If you do not, and an accident happens at any time during the vessels life, your organization will be held responsible for knowingly passing on defective product.
If the cracks are a result of your subsequent work, you need to thoroughly complete and document the repairs along with a full array of NDE and hydrotest reports, even if not required by the codes your working with, but just for "lawsuit" insulation.

Tim Gary

By darren

Date 08-09-2008 10:04

sounds like your in a game of hot potato there, give it back to whoever gave it to you before the music stops or you're out of the game.
do like what happens in our shop when these situations arise, someone spray paints a white elephant on it and it gets all the white hard hats buzzing.
just a thought
darren