A planned refinery turnaround is an operation of extreme density: hundreds of open lines, execution windows measured in hours, and a lost-production bill that can exceed a million euros a day. Sizing the welding crew correctly is not a logistics footnote — it is the variable that decides whether start-up lands on schedule.
Why welding sets the critical path
On a crude unit, FCC or hydrocracker turnaround, welding usually governs the critical path. Static equipment — columns, exchangers, fired heaters, process piping — concentrates thousands of joints that can only be executed once the equipment is dismantled, ventilated and covered by a hot-work permit.
The reference metric is the diameter-inch (dia-inch): a 6" Schedule 80 joint equals 6 dia-inch, but real time depends on wall thickness and process. A qualified pipe welder completes on the order of 25-40 dia-inch per shift in 6G with TIG root plus stick fill, and considerably more on small-bore piping. Counting the joints and translating them into dia-inch is the first honest step of any estimate. For work of this kind we deploy welding crews sized against that count, not against a round number. In Spain, where Sparks Service concentrates its activity, the maths is identical.
WPS, PQR and welder qualification are not the same thing
Before sizing anything you must know how each material will be welded. The WPS (Welding Procedure Specification) is the instruction for how to weld: process, filler, preheat, heat input, gases. That WPS is backed by a PQR/WPQR (Welding Procedure Qualification Record), which qualifies the procedure through destructive tests to EN ISO 15614-1 or ASME IX. The PQR never qualifies the person.
The welder is qualified separately by an ISO 9606-1 certificate (WQT), which fixes their range: process (111 stick, 135 solid wire, 141 TIG), material, thickness, diameter and position (1G to 6G). A welder holding 141 in 6G on carbon steel is not automatically cleared for duplex or 316L. Sizing means cross-referencing the joint matrix against the matrix of valid certificates — the most expensive mistake to discover late.
Counting heads: hours, ratios and overlap
The base formula is simple and unforgiving. Total dia-inch divided by productivity per shift, divided by the number of shifts in the window, gives the productive welders required. Real-world correction factors follow:
- Accessibility factor: scaffolding, confined spaces and work at height cut effective productivity by 20-40%.
- Helper/welder and grinder ratio: on process piping 1:1 or 1:2 is typical; without that support the qualified welder burns expensive time.
- Shift coverage: for 24/7 you plan 2-3 reliefs; with a learning curve and absenteeism, over-size by 10-15%.
- Repairs: a radiographic rejection rate of 3-5% already forces you to reserve repair capacity.
As a market order of magnitude, a qualified pipe welder in Spain runs around €28-45/h depending on process, material and regime; shift overlaps, travel and per-diems are budgeted separately and explain much of a turnaround's cost.
Exotic materials and quality control on site
Spanish refineries — the Tarragona (ChemMed) cluster, Petronor in Bilbao, Cartagena, Huelva or La Rábida — mix carbon steel with lines of 316L stainless, duplex/super-duplex and high-temperature alloys. Each family imposes rules: strict control of heat input and ferrite in duplex, back-purge gas and interpass control in stainless, post-weld heat treatment (PWHT) on heavy alloy sections.
Assurance is built on NDT — radiography, ultrasonics, dye penetrant — and inspection by EN ISO 9712 level II qualified personnel, inside an EN ISO 3834-2 welding quality system with EN ISO 14731 welding coordination. Our approach to quality and traceability starts by documenting every joint with its WPS, its welder and its test record.
48-hour mobilization: the factor that saves the date
The typical risk is not starting — it is the peak. When hidden lines surface as equipment is opened, or a radiograph triggers a wave of repairs, the window tightens and you need reinforcement in hours, not weeks. Here the ability of Sparks Service to mobilize certified welders to site within 48 hours turns a surprise into a planning adjustment rather than a start-up delay. We work to the certificate matrix required by engineering and supply personnel already qualified in the processes and positions of the scope.
Preguntas frecuentes
How many welders do I need for a turnaround? There is no fixed number: sum the dia-inch of every joint, divide by productivity per shift (25-40 dia-inch in 6G) and by the shifts in the window, then apply correctors for access, repairs and reliefs. Count joints first, then count heads.
Does the PQR qualify the welder? No. The PQR/WPQR qualifies the procedure to EN ISO 15614. The welder is qualified separately by an ISO 9606-1 certificate defining process, material, thickness, diameter and position.
Can the crew be reinforced once the turnaround is under way? Yes, and it is often necessary given repairs or emergent scope. With Sparks Service we mobilize certified welders to site in 48h, matched to the project's process and position matrix.
