New Manway, Gasket, and Weld Build-Up in One Outage: Classification Drives Everything

24 in. manway: alteration. It changes the tank's configuration and introduces a new opening that must be reinforced. Consequences: reinforcement designed to the current API 650 rules using the design thickness (not the measured thickness), weld details and minimum clearances from existing seams applied, certification updated by the organization performing the work with the authorized inspector's concurrence, examination of the neck welds, and a hydrostatic test before return to service. It is not simply "cut a hole and weld a neck."

Nozzle gasket: routine maintenance. No shell metal is removed and no weld is made, so it is neither a repair nor an alteration. It still requires positive isolation of the line, and the joint must be leak-tested before the tank is refilled.

Seam weld build-up: repair. It restores the shell to its design thickness without changing the design. Consequences: qualified WPS and welder, deposited metal at least restoring required thickness (confirmed by UT after grinding), PT/MT of the completed build-up, and a documented acceptance by the inspector. If build-up cannot restore the full thickness over the affected length, a flush patch or insert plate is the correct alternative, not thicker weld metal.

The classification matters because only the alteration pulls in the current-API-650 design check, new certification, and mandatory testing.

No. Three independent reasons:

1. No thickness margin. 0.24 in. equals t_min exactly. The heat-affected zone of a 24 in. opening, the reinforcement welds, and the pitting all sit in metal with zero allowance for either.
2. It lands on the defect being repaired. Placing a new opening above a seam that has thinned to 0.20 in. means welding into and around the repair, with overlapping heat-affected zones and no sound metal for the reinforcement.
3. Clearance. Only 4 in. from a horizontal seam is at or below the minimum clearance normally required between an opening/reinforcement and an existing butt weld, and the reinforcement pad would have to cross that seam.

Alternatives, in order of preference:

• Relocate the manway to sound plate in the second course (or the course above) with measured thickness comfortably above t_min, at least 3 in. clear of horizontal and vertical seams and clear of pitting.
• Repair the seam first, then install a full insert plate in sound metal and cut the manway through the insert. This gives a known thickness and a clean weld land.
• Reinforce with a pad designed to API 650 using the actual measured thickness of the surrounding plate as the starting point, and verify the pad lands on sound metal. Whatever is chosen, the reinforcement calculation must be done against the design thickness, and the finished welds must be examined.

Welding controls: WPS/PQR and welder qualification to the applicable code (ASME IX basis) with procedure review per API 653; preheat as required for the plate thickness and chemistry.

Examination:

• Manway neck-to-shell weld: PT or MT on the root and final passes, plus visual; verify the reinforcement dimensions against the design.
• Seam build-up: PT/MT of the finished surface and UT to confirm the restored thickness.
• Map the thinned seam beyond the 6 in. already found. A 6 in. thin spot is the visible portion of a longer corrosion cell.

Testing: hydrostatic test of the tank to the design liquid level after the alteration. Any substitution must be technically justified, approved in writing by the owner, and does not relieve the need for the weld examinations.

Documentation: repair/alteration description and sketches, WPS/PQR, welder qualifications, NDE reports, hydro test record, updated thickness survey and revised t_min, and the inspector's acceptance. Update the tank record and the inspection plan so the next inspector knows a 24 in. opening and a seam repair exist.