One short clause in the specification does most of the arguing

A pipe specification runs for pages of chemistry and dimensions, then one paragraph covers what will be done to prove the product is sound. On an ASTM A106 pressure pipe that paragraph lists four items: a bending test, in which a sufficient length of pipe is bent cold through 90 degrees around a cylindrical mandrel; a flattening test that is not required but which the pipe must be capable of passing; a hydrostatic test applied to every length without leakage through the wall; and a nondestructive electric test offered as the alternative to the hydrostatic test, applied to the full body of every pipe. Read that list and one question follows: which body examination is included, and what does each one find?

Hydrostatic and nondestructive electric testing are alternatives, not equivalents

The two are written as options because both are accepted routes to examining the body, not because they detect the same defect. A hydrostatic test loads the wall with internal pressure and finds anything that goes through it: a pinhole, a lap, a seam that failed to close. It cannot find an imperfection a third of the way through the wall. A nondestructive electric test scans the body and can pick up indications that never breach the surface, but its sensitivity moves with the method, wall thickness and diameter. The A335 P22 alloy pipe sheet carries both requirements side by side: each length is hydrostatically tested and each pipe is also examined by a non-destructive method, with the qualifier that the sizes examined by each method are limited by the scope of the respective practice. The seamless API 5L line pipe programme runs from 2 to 26 inches outside diameter in SCH 10 to XXS on the same principle; the welded-or-seamless decision behind it is covered in the comparison of ERW and seamless pipe.

Flattening, bend and squash test the forming the pipe will meet

These are ductility tests dressed as shop-floor operations. A53 pipe is described as suitable for welding and for forming operations involving coiling, bending and flanging, and its building-structure variant states that tension, bend and flattening tests confirm the mechanical properties of the standard. A106 asks for a 90 degree cold bend around a mandrel and treats flattening as a capability, not a routine. P22 makes the choice explicit: pipe whose diameter exceeds NPS 25 and whose diameter-to-wall ratio is 7.0 or less is subjected to the bend test instead of the flattening test, pipe of NPS 10 and above may be given the bend in place of the flattening subject to the purchaser's approval, and the specimens are bent at room temperature through 180 degrees without cracking on the outside of the bent portion. Duplex grades use a third vocabulary for the same idea: squash, extended, water pressure and crystal rot testing on the S31803 seamless pipe and S32205 seamless pipe sheets.

Sampling is written as a fraction of a lot, so the lot definition carries the risk

The quantity tested is rarely the quantity supplied, and the gap is where claims begin. P22 sets the rate by heat-treatment route: batch-furnace material is tested at 5 per cent of the pipe from each treated lot, at least one pipe for small lots, while continuously treated material is tested on a quantity constituting 5 per cent of the lot and never fewer than two pipes. One length out of twenty is a statement about a lot, not about the length delivered. The same arithmetic runs through the yield ladder of the API 5L X42 to X70 line pipe, offered in PSL 1 and PSL 2 from DN6 to DN1200 in 1 to 60 mm wall, and through the P91 alloy pipe range, supplied against ASTM or ASME SA335 with an IBR test certificate available, running 1/2 to 36 NB in 3 to 12 mm wall to 16,000 mm long. Large-diameter work shifts the question from test rate to inspection regime, which is how the large diameter thick wall stainless pipe range is quoted.

Third-party inspection is a set of signatures, and they are not interchangeable

Naming an inspector is not the same as naming a certificate. A mill certificate covers the mill's own testing; a witnessed certificate adds a second party at the test; a class society stamp adds a rule set. The duplex sheets show how the language is written: S31803 pipe and S32205 pipe both list inspection by TUV, SGS, BV, ABS and LR, while the stainless programmes carry SGS, BV, IQI, TUV, ISO and CE marks across the 310S pipe and 304 and 304L pipe ranges. The A53 building-structure pipe states simply that mill test certificates are issued to EN 10204/3.1B, the ordinary level; a 3.2 certificate means a designated inspector signed the results, and it is bought, not assumed. For sour and hydrogen duty the extra list on P91 — NACE MR0175, TM0177, TM0284, HIC, SSC, H2 service and IBR — is a separate decision again. The speciality sheets follow the same pattern: 317LMN tube, 317LMN grade, A213 / SA312 347 tube, 347H seamless pipe.

What the testing programme does not cover

Three things sit outside every certificate and account for most of the surprises. The first is the heat-affected zone: a certificate describes the pipe as delivered, while plate and pipe welding creates a microstructure no mill test examined. The second is the cut edge: mechanical cutting below 10 mm and hydraulic shear above it both leave a worked edge, and on stainless pipe that edge loses its passive film, as the square stainless tube and 302 tube finish lists note. The third is what follows testing: an unbundled pipe end left in the weather stains, and staining is not a mill defect. Where pipe is to be coated, preparation matters more than the coating, the argument set out on the surface treatment page. Duplex and super duplex families — 2205 seamless pipe, 2205 alloy, S32760 / F55 and 2507 — add a ferrite content check to the usual list, and it belongs on the certificate, not in a separate email.

Six lines that turn the clause into a purchase

Write these onto the enquiry and the specification looks after itself: whether the body examination is hydrostatic or nondestructive electric, and at what level; whether a bend or flattening test is required, and at what mandrel or ratio; the impact test temperature; the sampling regime if a lot release rather than a certificate is needed; the certificate level, 3.1B or 3.2, and the name of the inspector; and the surface condition the pipe is expected to arrive in. After that the route is short: carbon and low-alloy pressure duty to A106, A53 or A53 structural pipe; wet duty to the duplex and super duplex grades; high-chloride and mixed-acid duty to Alloy 825. Where bends and sheared ends are part of the order, keep plate bending, plate shear and steel cutting inside the test conversation and have the mill process to order. Leave the clause unread and the first failed pressure test writes it for you.