Quick Summary:
- A Factory Acceptance Test (FAT) for critical process valves is not a rubber-stamping exercise — it is the last opportunity to identify manufacturing defects, material non-conformances and assembly errors before the valve leaves the factory, and finding problems at this stage costs a fraction of finding them after installation or during commissioning.
- The core of any valve FAT is the hydrostatic shell test, seat leakage test and functional operation check, but for safety-critical and high-specification valves the documentation review — material certificates, NDE records, weld procedure qualifications — is equally important and frequently where the most significant non-conformances are found.
- An experienced, assertive inspection team that understands the applicable standard and what they’re looking for is worth more than the most elaborate FAT procedure document — inspectors who don’t know what to ask for, or who accept verbal assurances in place of documented evidence, undermine the entire purpose of factory inspection.
Why Factory Acceptance Testing Matters
Every significant process valve procurement project should include factory acceptance testing (FAT) — sometimes called manufacturer’s works inspection or pre-shipment inspection — as a contractual requirement. The purpose is straightforward: verify that the valve has been manufactured correctly, using the specified materials, to the specified dimensions and tolerances, and that it passes the specified performance tests, before it leaves the manufacturer’s facility.
Finding a problem at FAT is infinitely preferable to finding it after the valve is installed in a plant. Rework at the factory costs a few days and some remediation cost. Rework after installation on a live plant might cost weeks of production delay, scaffolding, permits, specialist contractors and operational shutdown. For offshore installations, the cost multiplication is even greater. The economic case for rigorous FAT on critical valves is not disputed by anyone who has experienced a serious post-installation non-conformance.
Beyond economics, FAT is a safety function. A valve that fails in pressure containment or leaks to atmosphere in a hazardous service creates a safety risk. The FAT is the engineering safety net that catches manufacturing defects before they become safety incidents. Treating it as a formality — a box to tick — misunderstands its purpose.
FAT Scope: What Should Be Included?
The scope of an FAT should be defined in the purchase order or inspection and test plan (ITP) that forms part of the valve specification. For different criticality levels, the scope varies:
For standard industrial valves in non-critical service, a document review of material certificates and test records, plus verification of the manufacturer’s own test data, is often sufficient. A third-party inspection visit is not economically justified for small volumes of standard catalogue valves.
For critical valves — ESD valves, SIS final elements, HIPPS valves, large-bore high-pressure isolation valves, cryogenic or sour service valves — a witnessed FAT by the purchaser’s inspector (or a contracted third-party inspection company) is essential. The FAT scope should include: documentation review (materials, NDE, welds), dimensional inspection, hydrostatic shell test (witnessed), seat leakage test (witnessed), functional operation test (witnessed), and verification of special requirements (antistatic, fire-safe, low-emission packing).
For valves with actuators and positioners, the FAT should include a complete functional test of the fully assembled valve-actuator-positioner package. An actuator tested separately from the valve tells you the actuator works; a valve body tested separately tells you the valve passes pressure tests. Only a combined test tells you the complete assembly works — that the actuator torque is sufficient for the valve, that the positioner calibration produces the correct valve position, that the fail-safe spring functions correctly, and that the partial stroke test sequence operates as designed.
Documentation Review: The Foundation of FAT
Before any physical testing, the documentation package must be reviewed and accepted. This is the aspect of FAT that is most often rushed or superficially done, and it’s where the most important non-conformances are frequently found — not in the physical tests (which the manufacturer has usually done correctly) but in the traceability and documentation trail.
Material certificates (Certified Material Test Reports, CMTRs) should be reviewed against the purchase specification for: compliance with the specified material standard (ASTM A216 Grade WCB, for example); heat number and lot number matching the valve bill of materials; chemical composition within specification limits; mechanical properties (tensile strength, yield strength, elongation) meeting the minimum values; impact test results if specified (at the specified test temperature, meeting the specified energy values); and heat treatment details if applicable.
The critical check is traceability: can you trace each pressure-containing component of the valve back to a specific heat of steel, and can you trace that heat to a test certificate that confirms it meets the specification? Generic test certificates (“this certificate covers all valves of this type”) are not acceptable — the certificate must be traceable to the actual heat of material used in the specific valves being supplied. Requesting serialised CMTRs for each valve by serial number is reasonable and should be specified on the purchase order.
Weld procedure qualifications (WPS and PQR per ASME Section IX, or EN ISO 15614 for European projects) should be reviewed for: coverage of the base materials being welded; coverage of the welding positions used; coverage of the filler materials used; and validity of the welder qualification records for the certified procedure. Welding performed outside the qualified range is a structural integrity concern and a code compliance issue.
Non-destructive examination records should show: the method used (radiography, ultrasound, magnetic particle, liquid penetrant), the technique, the equipment calibration records, the coverage (which welds were examined and to what extent), the acceptance criteria applied, and the results (accept/reject disposition for each examined area). Missing NDE records for required examinations is a significant non-conformance — it means the examination either wasn’t done or wasn’t documented, both of which are unacceptable.
The Hydrostatic Shell Test
The hydrostatic shell test confirms structural integrity of the pressure-containing envelope — body, bonnet and all body joints. The valve is pressurised to 1.5× the pressure rating at the test temperature (typically ambient) with water, held for the specified duration (typically 15 minutes for larger valves), and examined for leakage through the body wall, bonnet joint, and packing box.
No visible leakage is permitted during the shell test — any moisture on external surfaces that cannot be explained by surface condensation (from a cold valve in a warm, humid environment) is a failure. If there is any doubt, dry the exterior thoroughly with dry air before pressurising and re-examine.
The inspector should verify: the test pressure actually applied (cross-check the gauge reading against the specified test pressure calculation); the test duration (it must start timing after full pressure is achieved, not when pressurisation begins); and the test medium (water — using air or nitrogen for a shell test creates an unacceptable stored energy hazard if the valve fails catastrophically). The valve position during the shell test should be partly open (per the relevant standard) to avoid pressurising the downstream seat.
Seat Leakage Tests
Seat leakage tests verify that the closed valve seals adequately between upstream and downstream. The test procedure involves closing the valve, pressurising one side (upstream), and measuring the leakage rate from the open downstream side. The leakage must not exceed the class limit specified in the applicable standard (API 598, ISO 5208, API 6D seat leakage classes, etc.).
For Class A or bubble-tight shutoff, no visible bubbles in a submerged test, and zero measured flow in a metered test, is required. For less stringent classes, a defined volumetric flow rate per unit time is permitted. The inspector must understand which leakage class has been specified and apply the correct acceptance criterion — not the criterion the manufacturer considers “good enough.”
Soft-seated ball valves and butterfly valves should achieve Class A without difficulty in new condition. Metal-seated valves will typically achieve Class D to Class VI depending on design — metal-to-metal seating cannot achieve the zero-leakage specification of a soft seat, and the specification should reflect this realistically. Requiring Class A from a metal-seated valve that is physically incapable of achieving it causes test failures that require resolution by specification revision, not valve rework.
Directional tests (testing each seat from both sides independently) should be specified for dual-seated valves where the sealing capability from each direction is independently important. For DBB (double block and bleed) valves, testing each seat separately with the bleed valve open confirms that each seat independently holds the specified pressure.
Functional Operation Tests
For manually operated valves, the functional test verifies that the valve opens and closes smoothly through its full stroke, that end stops are correctly set, and that the operating torque (or handwheel force) is within the specified limit. For gate valves, the backseat position should be verified — the gate should close firmly against the backseat with the gate in the fully open position.
For automated valves, the functional test scope is substantially larger. The actuator should be connected to the plant instrument air (or equivalent) supply at the rated instrument air pressure. The complete operating sequence should be verified: open command produces full opening within the specified time; close command produces full closure within the specified time; fail-safe spring operation on loss of instrument air produces the specified fail-safe position; partial stroke test sequence operates correctly; positioner feedback signal corresponds to actual valve position throughout the stroke; and solenoid valve de-energisation (simulated trip signal) produces full fail-safe operation.
Operating torque under differential pressure is particularly important for control valves and ESD valves. Testing only at zero differential pressure tells you the valve is mechanically functional; testing at the rated differential pressure confirms that the actuator spring force is sufficient for the worst-case operating condition. Many FATs omit the differential pressure torque test because it requires a more complex test setup — but it’s precisely this test that confirms the actuator sizing is adequate.
Special Requirements: NACE, Fire-Safe, Anti-Static
For valves with special requirements, the FAT must include verification of those requirements. NACE MR0175 compliance requires hardness testing of all pressure-containing parts and trim materials — not just a certificate, but actual hardness measurements recorded and submitted. Hardness testing equipment must be calibrated; test locations must cover representative areas of each component (not just one measurement per valve).
Fire-safe qualification requires a test certificate from an independent, accredited test facility — not the manufacturer’s own test. The certificate must be traceable to the specific size, pressure class, materials and configuration being supplied. If the certificate was issued for a different size or configuration, the vendor must justify why it applies to the valves being supplied.
Anti-static testing for soft-seated ball valves requires measuring the electrical resistance between stem and body, and between ball and seat ring. This is a simple measurement (use a continuity tester) but it must be performed and documented. A missing anti-static spring in a valve — which won’t be detected by any other test — is revealed by this test. Resistance must be ≤ 10 ohms.
Issuing FAT Reports and Managing Non-Conformances
At the completion of FAT, a formal test report is issued recording all tests performed, results achieved, and any non-conformances identified. The non-conformance management process determines how identified problems are resolved: some are waived (the deviation is documented and accepted as not affecting fit for purpose), some require rework with re-test, and some are rejections requiring full replacement.
The inspector representing the purchaser must have clear authority to accept or reject valves, to waive minor non-conformances within defined limits, and to require re-work or re-test for major non-conformances. An inspector who doesn’t have this authority — who must refer every decision back to a project manager — cannot run an effective FAT. The authority level and decision criteria should be established before the FAT visit, not worked out in real time on the factory floor.
Summary
Factory acceptance testing is one of the highest-return activities in critical valve procurement. A well-planned, properly scoped FAT with experienced, empowered inspectors who know what they’re looking for will reliably catch manufacturing defects, material non-conformances and documentation gaps before they become field problems. The documentation review is as important as the physical tests — traceability of materials, completeness of NDE records, and validity of weld procedure qualifications are the foundations on which physical test results mean anything. Invest in FAT on critical valves; treat it seriously; and you will spend that investment many times over in avoided field problems.