Vessel Integrity Check

You should ask a certified engineer to make a "fracture analysis" computation in order to determine taking into consideration loading the further evolution of the crack and the life expectancy of the vessel.

For some materials even a low depth crack can be dangerous. You should consider that the crack growth rate is proportional (in some phases over linear) with its depth and there is a critical depth when speed reaches the speed of sound.

The 24mm crack - if it is crack is likely to be extremely hazardous.

The cracks will propogate very quickly under the favourable circumstances (ie shock/fatigue)

The shocks may be mechanical (vibration, pressure fluctuation,...) , thermal or any other type that has an effect on the material stress.

Secondly where is the crack? Most likely it will be in the circumferencial weld or HAZ?

As #1 said you may carry out an analysis of the vessel by an expert for the critical defect size corresponding to the stress. But as far as the norms go : cracks or linear indications of any size are not permitted.

I agree nick name and Guest for there posts #1 & #2.

For cracks, no way to wait because of the failure of vessel is very expected at any time due to the sensitivity of cracks to propagate. An authorized firm to do the repair is requested to start immediately to open the crack up to sound metal with the optimum joint design and fellow the WPS's & PQR's and recommendations of the authorized inspector.

Note. An ultrasonic/or similar check test is required to cover many areas of that vessel.

1. Determine the stresses that act across the flawed region.

2. Determine the operating cycle for the vessel as well as the number of these cycles that the vessel will see for the remainder of its planned use.

3. With this information in hand, engage the services of a fracture-mechanics analysist who will determine the safe remaining life of the vessel.

If this is an ASME Code Stamped vessel, then you can check the code calculations, or the Code book itself, for the minimum wall thickness for the service. If the minimum wall thickness is not compromised by the depth of the crack, you can grind it out without any further concern. However, if it is a Code vessel, the AI must be consulted before any repair work requiring welding is performed. If it is not a code vessel, you may have recourse to the OEM for their advise regarding the cracks ( which sound like "creep" caused by IGSCC due to some contamination). You didn't state if the flaws were near the HAZ. Dedpending on the thickness of the plate, repair by welding may require PWHT, regardless whether it is or is not a Code vessel. If the intent is not to do anything, you may want to distance yourself during operation.

One "proviso" to my comment: If grinding is the only thing you do, I recommend that you follow it up with a Mag. Particle examination to assure that the crack has been completely removed.

Its Code stamp vessel; the crack is found on the vessel wall NOT on the weld joint.

Please can you help with the Code calculations you mentioned?

Thanks

I agree with everyone else here. If this is a crack, it could cause further damage.

However, you say "crack-like defect." Is it a crack or is it just some loss of wall thickness?

Even if this is not a crack, you should use some code calculations to back up your judgement. ASME Section VIII is for the design of vessels. API 510 is for repair or rerating of vessels and API 579 is a Fitness-for-Service. You have to prove that your judgement is correct.

Regarding the thickness of shells under internal pressure, please refer to ASME Section VIII, Division 1, paragraph UG-27. In this you will find most, if not all, the information you need to determine if the minimum shell thickness is compromised. Also, you will need the CMTR (Certified Material Test Report), or MTR (Material Test Report) issued by the plate manufacturer/supplier to check the nominal wall thickness; and, take into account any corrosion allowance. Check the area for evidence of "arc strikes" as these may cause these crack-like structures due to poor manufacturing techniques - they cause localized hardened areas that are stress risers and susceptible to form indications as you have described. If this is not the case, then you may want to investigate the area by grinding it out until it disappears - use MT - and then check the wall thickness for the minimum required for the intended service. The OEM should be able to help you with this by offering additional advise.

i think that it's important to define the extension of the defect and the fitness for service (API 579) bal also you should define what is cause of the crack.. i mean if it's due to a corrosion mechanism then you can define corrective measure to control asnd stop it..

Vitt

corrosion & rust prevention