Scheduling Tank and Pressure Vessel Fabrication Around Certified Welders

A vessel shop is not constrained by steel or by machines, it is constrained by bays, certified welders, and a stress relief furnace that runs one load at a time. EDGEBIC by User Solutions counts the bays as finite positions, routes each weld step only to a welder holding the qualification it requires, and carries radiography and heat treat hold points as real time on the calendar.

Long single-piece jobs break most scheduling software. The steps run for weeks, the resources are people with credentials, and half the routing is waiting for something that is not labor at all.

Bays Are the Capacity

Four fitting and welding bays with vessels occupying one for five or six weeks gives you roughly 34 bay-weeks a quarter. That is the plant, and it does not expand because a spreadsheet says everything fits.

Model each bay as a unit of a fabrication work center and put the real step durations on each vessel's routing. The engine places every vessel against the real bay positions and flags any order that cannot claim one in time, naming the step that failed to fit. Multi-week steps span shifts and weekends according to that bay's calendar rather than resetting at the end of each day. See multi-resource capacity planning for the general shape and finite versus infinite capacity scheduling for why the distinction matters.

Partial progress carries forward. A shell that is 60 percent welded stays 60 percent welded through the next reschedule instead of restarting on paper: see how partial completions carry forward.

Weld Procedure Qualification Is a Scheduling Constraint

Code work means the welder has to be qualified on the procedure, the position, and often the material. A schedule that treats every booth as interchangeable will place work that nobody on the roster can legally perform, and the discovery happens at the worst moment.

Model the qualification as a skill, assign it to the welders who hold it, and require it on the routing step. The scheduler places that step only in shifts where a qualified welder is rostered. If your only welder qualified on a particular overlay procedure works Monday through Thursday, overlay work lands on those days. When someone is out, remove them from the roster and reschedule: the affected steps move, and any vessel that can no longer make its date is flagged. Completed work is never moved by that reschedule, so the record of what was already welded and signed off stays intact.

You can pin a specific vessel to a specific welder when a customer or a procedure demands it, and that pin survives every later reschedule. The same certification model is described in operator certifications for welding shops.

Hold Points Are Time, Not Labor

Radiography turnaround, PWHT cooldown, hydro fill and soak, and inspector availability all consume calendar without consuming a welder. Schedulers that count only labor hours delete them, and the promised date is short by exactly the amount of time nobody scheduled.

Put the hold on the routing as queue time, a shift-aware buffer placed after the operation and before the successor may start. A two-day radiography turnaround lands as two real days. For the stress relief furnace, model it as a work center with real units and flag it as one job per day, because it runs one load per cycle rather than a bucket of hours. The batch pattern is the same one used in heat treating furnace scheduling.

Anchoring on the Furnace

On most vessel shops the shared furnace is the true constraint. Flag it as your bottleneck work center and give the constrained vessels a target date. The engine then anchors the plan around the furnace slot: fitting and welding are timed to feed it and hydro test, paint, and shipping are timed off its completion. Vessels that cannot claim a slot before their promised date are flagged weeks ahead. See how to flag and schedule around a bottleneck and why the bottleneck sets the pace.

When you need one extra weekend cycle, a daily capacity override adds it on a single date without changing the permanent calendar. Reschedule and read how many vessels that one cycle rescues before you authorize the crew.

A Worked Vessel

One ASME vessel, promised 14 weeks out.

Two hold points and one furnace slot account for three days and a bottleneck cycle that a labor-hours plan would have shown as free. The vessel is confirmed or flagged on that basis, not on a rolled-up hour count.

Tracking a Six-Week Step

Welders log start, stop, and progress at a shop floor station, so a seam weld running behind pushes only the work that has not started. Because completed operations are never moved by a reschedule, running the plan weekly is safe on a job that has been in a bay since last month. Over a few vessels the logged data tells you what your real weld deposition rate is by procedure, which is the number your estimating department has been guessing at.

Heritage in Code and Program Work

User Solutions has built finite capacity scheduling since 1991, more than 35 years, for operations where certification, inspection, and long durations all constrain one plan: US Navy, GE, BAE Systems, and Cummins across 33 locations. The lineage behind EDGEBIC, including the RMDB heritage, coordinated the Nimitz refit at more than 26,000 tasks, an environment of qualified trades, hold points, and fixed positions. A vessel shop running four bays against a shared furnace is the same discipline at a scale one planner can hold.

Where to Start

Count your bays as real units, add the three or four weld qualifications that genuinely gate work, put your radiography and cooldown holds on the routings as queue time, and flag the furnace as one job per day. Then schedule the quarter and read the flagged list. The first honest bay-week number is usually the most useful thing the exercise produces.

For fundamentals, what is production scheduling is the plain-language start and job shop labor scheduling covers the people side. The industry fit guide maps neighboring sectors and EDGEBIC is the product hub. Ready to find out how many vessels your bays really support? Contact US for a demo.