Why the scope argument arrives late
A pipe spool is a section of pipe cut, fitted and welded with flanges, elbows, tees or branches, delivered to site ready to bolt in. The enquiry usually arrives as a set of isometrics and a request for a price per tonne. The first real conversation then happens when the first spools are offered for inspection and both sides discover they had different ideas about what fabrication to drawing includes.
Welding skill is rarely the problem. The gap sits in scope: who supplies pipe and fittings, who turns isometrics into spool drawings, which welds are radiographed, who pays for heat treatment, who runs the pressure test, and who carries the cost when a spool reaches site and a flange does not line up with its partner. All of that is knowable before the order is placed, and cheaper to settle then.
What the spool drawing has to settle
An isometric describes a line. A spool drawing describes the piece that will be built, and it needs information the isometric does not carry: cut lengths, spool break points, field weld locations, branch orientation, and where supports land relative to the welds.
Three decisions sit on the drawing and change the price:
- Where the spool breaks fall, because a break at a sensible transport length costs less than one that follows the isometric sheet boundary.
- Which joints are shop welds and which are field welds, since every field weld takes work out of the shop and adds fit-up risk on site.
- Whether the drawing fixes flange bolt hole orientation, because a flange rotated by one hole is a rework item rather than a site adjustment.
A buyer who sends isometrics only and expects the fabricator to produce spool drawings should price that engineering separately, with a review cycle. A buyer who sends spool drawings should still expect a comment sheet before material is cut. A shop that starts cutting without commenting has either read the drawings carefully or not at all.
Pipe, fittings and traceability
Material supply is the largest single variable in a spool order. Buyer-supplied pipe and fittings keep material cost visible and let the buyer use an existing frame agreement. Fabricator-supplied material is simpler to administer but moves the certificate trail and the schedule risk to the supplier.
Either way, the order should name the certificate type. EN 10204 type 3.1 certificates, which report test results from the actual heat, are the normal requirement for pressure and process work. Type 2.2 reports are not interchangeable with them, and a quotation that does not say which one it includes is quoting a different product from the one most specifications call for.
Traceability then has to survive the shop. Heat numbers are transferred to cut pieces, recorded against the weld map, and carried through coating and dispatch. Where the specification requires it, the finished spool carries the heat number in the marking, so a later repair can be traced back to the mill certificate.
Welding: procedure, qualification and the weld map
A shop working to ISO 3834-2 has a welding quality system covering procedure specifications, welder qualification, consumable control, inspection and records. That is the framework worth asking for by name, because it describes how the shop controls welding rather than what it can weld.
Two documents sit under it on a spool order. Welding procedure qualification records to ISO 15614-1 prove the procedure produces sound joints at the material and thickness in question. Welder qualification to ISO 9606-1 proves the individual can deposit that joint in the position the drawing requires. A shop with a good procedure and an unqualified welder working overhead has a problem the paperwork will not reveal, which is why welder identification on each joint is worth requiring.
The weld map ties the two together. It numbers every joint on the spool, records who welded it and to which procedure, and points to the inspection result for that joint. Without a weld map, NDT coverage becomes a percentage of an unknown total, and repair history disappears.
NDT and heat treatment: decide who does what
Non-destructive testing on pipework is normally specified as a percentage of welds by joint category, with certain joints at one hundred percent. The percentage is a design decision that comes from the piping class and the service, not from the fabricator.
What the fabricator controls is execution and evidence. Many shops hold visual and penetrant testing in house and place radiography and ultrasonic testing with a specialist. That is normal, provided the order says so and the reports arrive identified to the weld map.
Post-weld heat treatment follows the same logic. The piping code and the material set the requirement, the thickness tables decide whether it applies, and the shop either has a furnace that accepts the spool or sends it out. A spool that needs treatment and misses it is not a cosmetic defect: the hardness in the heat affected zone is wrong, and the repair is expensive.
Pressure testing: shop or site
ASME B31.3 requires new piping to be leak tested, with a hydrostatic test at not less than 1.5 times design pressure as the default, corrected for temperature, and pneumatic testing allowed only where the hydrostatic route is impractical and under a written procedure. The code permits the test on a completed system rather than on individual spools.
That flexibility is where scope gets lost. Testing spools individually in the shop proves the shop welds but needs end caps, water, a test bay and a drying step, and it says nothing about the joints that will be made on site. Testing the assembled system on site proves the whole line but moves cost and schedule risk to the erection contractor, and a leak found at that stage is expensive to reach.
Smaller orders often test a percentage of spools and leave the rest to site. Whatever the split, the enquiry should state it, name who supplies the test medium and calibrated gauges, and say whether the test report is a delivery document.
Supports, guides and the parts that are not pipe
Pipe supports are usually bought with the spools and priced separately, and they carry their own specification. A shoe welded to the pipe, a trunnion, a dummy leg, a guide or a limit stop all attach to the pressure boundary, and that attachment weld is a pressure weld with its own inspection requirement.
The steel part of the support, whether a rolled section, a fabricated bracket or a base plate, is ordinary structural fabrication and can be made to a dimensional drawing. The interface between the two is where errors survive: a shoe whose height is measured from the wrong pipe centreline, or a guide that fouls the insulation thickness, will be found on site.
Spring supports and constant hangers are normally bought from a specialist and set at site. The spool order should still identify where they land, because the fabrication has to leave the pipe free of welds and supports in that zone.
Dimensional control before dispatch
The checks that matter on a spool are the ones that decide whether it bolts up. Overall length and branch positions are the obvious ones. Flange face squareness to the pipe axis, bolt hole alignment across the pair, and the flatness of a mating face are the ones that get missed, and they are the ones that cannot be corrected on site without cutting.
ASME B31.3 sets limits on flange alignment and on joint fit-up, and project specifications usually tighten them. A shop that measures at least the flange faces and records the results is doing what the code expects. A shop that measures nothing is relying on the fitter.
Where several spools must arrive in sequence and connect to each other, a trial fit in the shop turns a site problem into a shop problem. It costs crane time and floor space, and it is worth it once the spool count passes single figures.
Marking, packing and the sequence site needs
Spool marking should match the drawing and line numbers and stay readable after coating. Ends are protected, gaskets and bolting are fitted or packed by spool, and the packing list follows the erection order.
Coating is its own scope decision. Shop primer with a stripe coat on welds, a full system in the shop, and no coating are three prices and three delivery dates. If the site will blast and coat after erection, say so, because primer that has to be removed is wasted money.
What goes in the RFQ
- Isometrics, spool drawings where they exist, and the piping class for each line.
- Material grades, pipe schedule, and whether pipe and fittings are buyer or fabricator supplied.
- Certificate type required, named by EN 10204 grade.
- Welding standard and quality requirement, plus any project welder qualification.
- NDT methods, coverage by joint category, and who performs them.
- Heat treatment requirement and the code table that sets it.
- Pressure test method, pressure, medium, and whether it happens in the shop or on site.
- Support drawings, attachment weld requirements, and who supplies spring units.
- Surface preparation and coating system, with dry film thickness and the governing standard.
- Marking format, packing method, delivery sequence and the receiving address.
Who decides what
| Decision | Owner | Why it sits there |
|---|---|---|
| Spool break points and field weld locations | Drawing owner | Affects erection sequence and site cost |
| Spool drawing production | Negotiated | Either party can do it, but only one is paid for it |
| Material grade and certificate type | Drawing owner | Tied to the piping class and specification |
| Welding procedure and welder qualification | Fabricator | Part of the quality system being purchased |
| NDT coverage | Drawing owner, to the code | Follows joint category and service |
| Heat treatment requirement | Drawing owner, executed by fabricator | Set by material and thickness, not preference |
| Pressure test location | Negotiated and stated | Changes cost, schedule and risk allocation |
| Coating system | Drawing owner | Depends on site conditions and service |
Where the order should land
A pipe fabrication order is a drawing order with a welding process attached. The drawings decide what is bought, the welding documents show how it was made, and the test decides whether it leaves the shop. Settling those three in the enquiry takes a few hours and removes most of the disputes that otherwise surface at inspection.
Realjet carries out welded fabrication to customer drawings, covering cutting, forming, welding under ISO 3834-2 and machining of interfaces, with trial assembly where the geometry calls for it. The contract manufacturing capability page sets out the process scope and the route for sending a drawing set for review, which is where the questions above get answered against a real order.