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Hi All, During the hydro testin

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metboss

metboss

Petroleum
Joined
Sep 12, 2012
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153
Location
AE
Hi All,

During the hydro testing of Wellhead equipment ( 5,000 psi test pressure; code reference API 6A), pressure started dropping and observed a leak in one of the plugged port (threaded type). Upon visual inspection, a linear crack (1.5") was identified on an entire threaded area of port. This threaded port was drilled into Wellhead body for seal testing purpose.
I have asked them to carry out LPI on threaded area to see the extent of crack followed by machining. It was done and there is no more trace of crack now.

Raw material MTC (AISI 4130) review reveals no lamination or internal defects reported in it. However, in my opinion, it may be due to raw material defect and requested the vendor to carry out "an additional UT test (entire body) to verify the integrity and re-hardness test as it was already undergone cladding & PWHT during manufacturing".

Based on your expertise, please advise on below:
•What might be the root cause for such linear crack (raw material defect or due to heat input from welding??)?
•Can I request for any additional test?
•What should be the remedial action/corrective actions so that we can ensure the safe operation of equipment under rated working pressure (5,000 psi) in field?


 
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Was the threaded port part of the original design or was it added for testing purposes?
 
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It is a part of original design.

Thanks
 
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It is difficult to guess the cause of the crack from the information provided. A raw material defect (in the forging or casting) is possible.

Are you the manufacturer or the purchaser of the equipment? If you are the manufacturer, you can do whatever additional (non-destructive) testing you want. If you are the purchaser, you can request whatever you want, but the manufacturer can also reject your request unless your contract requires them to fulfill it.

If the threaded area was machined away to remove the crack, does the product still fulfill the design requirements (which presumably included a threaded port)?
 
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We are the purchaser of equipment.
After threaded area was machined our for defect removal, it was completely plugged. A new hole is drilled now. My concern is on hidden internal raw material defect(if any) which may appear during the service life of equipment (5,000 psi).
When we checked the raw material UT report from manufacturing QC dossier, neither any laminations nor any internal defects were reported in it. How could the linear crack suddenly appear when it exposed test pressure?
 
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So 1 1/2" deep into the casing or 90 degrees from the edge?

Was it all in the thread?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
 
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Why not just machine out the crack and use a larger port plug? Are you sure it was a crack and not a bad machined thread? Very odd there would be a crack on a machined thread. I'd suggest MP 100%. What is the PSL rating?

Petrotrim Services, LLC
 
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I am not sure what direction you saw the crack, or how big it is, even assuming there are other cracks like it, you probably won't see it with UT/RT.

These defects exists in almost all material. Forged products simply folds and reduce these defects. if the valve already passes, multiple times, hydrostatic testing. The chance of the valve failing in the field is near zero. Many valves out in service today are filled with micro defects, if not bigger defects.

The best practice i can recommend is just to double check other valves just like it, focus some UT/RT near the same location to see if it's systemic defect (highly likely not), and move on. Or you can require PT of the machined thread area for that lot, just to double check.


Luke | Valve Hax |
 
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Hi,

Thank you all for valuable advice.

Jus to update: UT and LPI was done on machined out area and no further defects found. Also, UT was done on all accessible surfaces of Equipment and no defects found. After repair, Equipment was subjected to Hydro test and passed successfully. Finally, it is accepted by ENGG Team as well.

Thanks again!


 
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Since there appears to be no obvious metallurgical cause, you should consider operator error on the test stand. Was this connected to a data logger or are readings taken by hand? A quick transient a above 5k psi could have triggered the failure.
 
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