Hello all,

We want to add RF pad to one of the nozzles on pressure vessel. Vessel is 10 years old. We will weld RF pad in 2 halves around the nozzle neck.
My question is - Is it necessary to carry out hydrotest of whole vessel after RF pad welding or only pneumatic test of RF pad is sufficient?

Regards,
Deepak Mhatre

I think you need to perform hydrostatic test of complete vessel.
Refer UG-99(a).

Your answer would be correct if it was a ASME Sect. VIII prssure vessel. A used item is outside the scope of ASME. You may refer to the NBIC, in which case alternative tests may be performed instead of the hydro. You may perform pneumatic test as you propose.
Mauro

My question is - Is it necessary to carry out hydrotest of whole vessel after RF pad welding or only pneumatic test of RF pad is sufficient?


Deepak,

To perform hydrotest on a ten years old vessel is more harmful and air bubble test of the RF pad welding is sufficient to determined the tightness of weld.

NBIC rules states "It is judgement of the AI if hydrotest is warranted for this type of repair".

leem817

I agree Leem, clear it with your AI.

Recently had same situation and AI let me use pneumatic test with "snoop" for leak detection.

Robert P
QA Manager

Well, I understand it is a repair, but, why adding a reinforcing pad? You have to establish with the AI the repair program and relevant final testing and examination. The friend who wrote here that hydrotest could be dangerous should consider how dangerous could be the service.
This is not an argument to justify the absence of hydrostatic testing. Do hydro if you can, otherwise be sure that the vessel is in condition to sustain the most severe service conditions. Downrate if you are not sure, but do not let an item enter in service if you are not sure it is safe.Think this: would you bring your family for a picnick beside this vessel in service? If not, do what you think better and ask to those who know better than you, and send the pressure vessel in service SAFE.
Regards.
Mauro
Regards.
Mauro

What do you mean for pneumatic test of the pad?
I am afraid you misunderstand the meaning of this test.
This test has the scope of verifying the tightness of the weld between the nozzle and the shell. ONLY THAT
The procedure consists in introducing low pressure air through the tapped hole in the RF and apply the soap solution inside the tank in way of the corner joint of the nozzle to the shell.
I know some Inspectors (Not AI I hope) require to apply soap all around the external welds of the pad: this is a nonsense. if you want to avoid discussions do it, but do not forget to apply soap in the only position where you need: inside the vessel at the root of the nozzle to vessel weld. Please read UG-37. Also concerning when you apply a split RF

(g) Reinforcing plates and saddles of nozzles attached
to the outside of a vessel shall be provided with at least
one telltale hole [maximum size NPS 1⁄4 (DN tap] that
may be tapped for a preliminary compressed air and soapsuds
test for tightness of welds that seal off the inside of
the vessel. These telltale holes may be left open or may
be plugged when the vessel is in service. If the holes are
plugged, the plugging material used shall not be capable
of sustaining pressure between the reinforcing plate and
the vessel wall.
(h) Segmental reinforcing elements are allowed provided
the individual segments are joined by full penetration
butt welds. These butt welds shall comply with all the
applicable requirements of Part UW. Unless the provisions
given below are satisfied, the area A5 as defined in
Fig. UG-37.1 shall be multiplied by 0.75. The area A5 does
not require any reduction if one of the following is satisfied:
(1) Each butt weld is radiographed or ultrasonically
examined to confirm full penetration, or
(2) For openings in cylinders, the weld is oriented at
least 45 deg from the longitudinal axis of the cylinder.
Each segment of the reinforcing element shall have a
clear path to a telltale hole and shall be tested as required
by UG-37(g).