Pressure Vessel Procurement and Inspection
Previously, Decundi Inspection Services has been awarded a contract to purchase several heavy wall pressure vessels (thickness greater than 1-7/8") made from SA-516-70N material. In addition, the scope for the procurement of these pressure vessels includes Decundi coordinating with the vessel fabricator to carry out the pre-inspection meeting and also to carry out inspections during the fabrication, post-weld heat treatment, and testing of the pressure vessels.
The dimensional inspection was carried out for the wall thickness, outside diameter, and length of the cylinders for two (2) of several pressure vessels (refer to 30" Ǿ heavy wall below) commented about within these narratives where the primary vessel spoke about is noted to be a 24″ diameter heavy wall pressure vessel on saddles and with 2:1 elliptical head. Decundi inspection personnel apply due diligence and go above and beyond the usual inspections checks carried out during the fabrication of pressure vessels, and in this regard, for pressure vessels procured and inspected for Decundi's client, that benchmark dimensional inspection was carried out for the wall thickness of the 24" diameter vessel and was carried out using a Starrett digital caliper. The wall thickness was found to be 1.883" thick. The required wall thickness for this 24" Ǿ vessel is noted to be 1.875" thick.
After rolling the cylinder and prior to welding the long seams, Decundi inspection personnel carry out an inspection for the weld preparation at the long seams for compliance with Section IX, QW-402, as stated in the welding procedure. For the case of the aforementioned 24" Ǿ heavy wall pressure vessel, the weld preparation was noted to be a double V-groove at the long seams on the cylinder. Also, a dimensional inspection of the weld preparation at these long seams was found with a 31° double bevel, a 62° included angle, a 1/16" landing, and zero (0") root opening. Visual inspection of the weld preparation found the surfaces to be smooth with no erratic profile, chatter, or kerf from torch cutting was noted.
Before the commencement of welding, Decundi inspection personnel carry out an inspection for the welding electrodes used for the deposit of the root pass, fill passes, and cap bead at the long seams. Verification is made that the welding electrodes for the root pass found the consumables to be 3/32" Ǿ E7018-1 (SMAW process), and in addition, an inspection of the 3/32" Ǿ E7018-1 electrodes found these low-hydrogen electrodes were contained in hermetically sealed containers. Decundi also assures that the welding rods are in good condition, with no damage noted to the coated shielding (flux) on the welding rods. In addition, Decundi inspection personnel also confirm that after opening the hermetically sealed containers, the electrodes are stored in an oven held at a temperature of at least 250 °F (120 °C) as required by AWS D1.1.
The assigned inspector for the fabrication of pressure vessels inspects for 1″ clean back at the toe of the long seams and girth seams on the I.D. and O.D. and at the openings for all nozzle and manway attachments where this clean back is required for mitigating possible weld defects. During the fabrication of heavy wall pressure vessels, Decundi inspection personnel verify that prior to deposit of the root pass, preheat is applied at the long seams, girth seams, and the openings for all nozzle and manway attachments and to the correct temperature as stated on the WPS.
Verification is made for proper cleaning of the deposited weld at the root bead at the joints commented on above (refer to long seams, girth seams, nozzles, and manway) for removal of the slag, following which, inspection is carried out for verification that the root bead is free of defects such as porosity or crack. For the fill passes and cap bead, an inspection is carried out for the welding consumables for submerged arc welding. Decundi inspection personnel also carry out an inspection for assurance that back gouging at the joints is carried out to sound metal plus smooth grinding of these surfaces, and also MT is carried out before deposit of the fill passes and cap bead from the opposite side of the joints. We monitor the amperage and voltage during welding, plus verification that proper interpass cleaning is carried out after each fill pass by SMAW and SAW processes throughout the completion of the weld. Inspection is also carried out for the weld reinforcement at the I.D. and O.D. at the long seams and girth seams for compliance with ASME Section VIII Division 1. Decundi inspection personnel also carry out an inspection for re-rolling of the cylinders of a 24″ diameter heavy wall pressure vessel and 30" Ǿ heavy wall pressure vessel using a sweep board for the permissible out-of-roundness as required by ASME Section VIII Division 1, paragraph UG-80 (a) (1).
Inspection is carried out for the 2500# RTJ, RFLWN nozzles installed on the vessels, and benchmark thickness measurements are taken for the wall of the nozzles and also that the ring groove is free of damage such as arc-strike, scratches, and dents. Decundi inspection personnel carry out the final dimensional inspection of pressure vessels for assurance that the vessels are fabricated as per the drawing, following which hydro testing is carried out, plus abrasive blasting and painting.
