Valve Testing and Certification: Factory Tests, Witness Tests, and Type Tests

The Testing Hierarchy for Valves

Valve testing is organized into three categories: (1) routine production tests performed on every valve, (2) witness tests where the customer or third-party inspector observes specific tests, and (3) type tests performed on a sample to qualify a new design. Understanding this hierarchy helps engineers specify the correct testing requirements in the purchase specification.

Routine Production Tests (API 598)

API 598 (Valve Inspection and Testing) is the primary standard for routine testing of process valves. Each valve must pass: (a) shell test at 1.5× rated pressure, (b) seat closure test for each seat at 1.1× rated pressure (soft-seated) or 1.1× rated pressure (metal-seated with permitted leakage rate), and (c) backseat test (where a backseat is provided). Tests must be conducted with water, or alternative fluid as specified.

Witness Inspection and Testing

• Customer or third-party inspector observes testing at the factory

• May include NDE of materials (PMI, UT, RT) in addition to pressure testing

• Addition of witness adds cost and schedule due to inspector travel and hold-point coordination

• Common for critical valves in refineries, chemical plants, and power generation

• Specify witness requirements clearly in the purchase order

Type Testing of Prototype Valves

Type testing qualifies a valve design before production. Standards that require type testing include: API 607 or 6FA (fire test on a prototype valve to demonstrate post-fire leakage limits), ISO 15848 (fugitive emission type test), API 6D (pipeline valve design qualification), and ASME QME-1 (nuclear valve seismic qualification). Type test data is retained by the manufacturer and referenced for production valve certification.

Additional Tests Often Specified

• Positive Material Identification (PMI): confirms alloy composition of each part

• Hardness testing: required for NACE MR0175 sour service compliance

• Helium leak testing: for cryogenic and high-vacuum applications

• Torque testing: measures actual operating torque at rated pressure

• Functional test with actuator: confirms actuated valve performance at rated conditions

Documentation and Certification

Test certificates are required deliverables with the valve. EN 10204 defines the common certificate types: 2.1 (Declaration of compliance by the manufacturer), 2.2 (Test report by the manufacturer), 3.1 (Inspection certificate by the manufacturer's independent department or laboratory), and 3.2 (Inspection certificate by both manufacturer and customer-appointed inspector). Specify the certificate type required in the purchase specification.

Summary

A clear specification of required pressure tests, NDE, witness points, and documentation ensures that valves delivered to site meet all quality and safety requirements. The incremental cost of rigorous testing is small compared to the consequence of a valve failure in service.