Everybody might know that the general practice/procedure is to perform hydrotest on a vessel before painting.
However, there are special cases where the general practice, project spec even, may not be complied with. This will be subject to Client’s approval of a submitted deviation or concession, in justification of satisfying something like meeting the planned equipment delivery.
On this case, an ASME pressure vessel in water service has been fabricated and now needs to be completed urgently in time for air freight. However, the challenge is to meet the schedule considering the vessel had just finished fabrication, have not been painted nor hydrotested.
Painting is done by Vendor X, while fabrication and testing is done by Vendor Y. Vendor Y advised that they cannot accommodate hydrotesting of the vessel until a couple of days later due to high volume of work at their shop. Drying of paint can take a lot of hours if not days depending on the coating system applied.
To cut the story short, it has been decided by all relevant parties to have the vessel painted first in order to make up on lost time, and then hydrotested, delivered and then do touch up paint at site/yard. Most authorized inspectors (AI) do not allow this as it has risks involved.
Hydrotesting is done to test the leak tightness of the vessel and its weld joint strength. Painting has the ability actually to plug and seal off small pin holes and other defects. During hydrotest, leaks normally occur on joints. It will be easier to spot and prevent sealing of small holes on these areas if it is not painted. However, doing stripe coating/touch-up paint of the welds at site after hydrotest might impact the integrity of the paint.
As per UG-99 (k) of ASME Section VIII Div. 1, painting before hydrotest is allowed but with some restrictions and a bit of caution.
It ended having the vessel painted except for welding joints as you can see on these photos. It’s hard to say whether that process has been successful as I had not heard anything back after the vessel was delivered.
There might be some quality vs. schedule debate here. If you were to decide, what would you do differently? Let us know what you think by putting your comments below.