A commercial invoice and a material certificate tell you what the manufacturer says it built. Third-party inspection (TPI) is how a buyer confirms it independently — an accredited, uninvolved inspection body checks the equipment against the purchase order and the applicable standards, before it ever leaves the factory.
What a TPI agency actually does
Scope varies by equipment and contract, but a typical TPI assignment for oil and gas equipment covers:
- Material verification — reviewing mill certificates and, where specified, positive material identification (PMI) testing
- Dimensional inspection against the approved drawing
- Non-destructive testing (NDT) — visual, dye penetrant (PT), magnetic particle (MT), ultrasonic (UT) or radiographic (RT) as called for by the code
- Witnessing hydrostatic (pressure) testing
- Witnessing the performance test, for rotating equipment such as pumps
- Final visual inspection, marking/nameplate verification, and painting/coating check
- Reviewing and stamping the manufacturer's data book / documentation package
Witness, monitor, or review only?
Not every inspection needs a fully witnessed test, and the level you choose changes both cost and lead time. The common levels, from most to least involved:
Witness (hold point)
The inspector must be physically present for the specific test — production cannot proceed past that point without the inspector's sign-off. Used for critical tests such as hydrostatic and performance testing on major equipment.
Monitor (notification point)
The manufacturer notifies the inspector of the schedule, but the test can proceed if the inspector does not attend. Used for less critical stages, or where random or spot inspection is acceptable.
Document review only
The inspector reviews test records and certificates after the fact, without attending in person. The lowest-cost option, generally reserved for lower-criticality items or where the manufacturer has a strong track record.
Who are the TPI agencies?
A handful of internationally accredited inspection houses cover most oil and gas equipment inspection worldwide, including Bureau Veritas, TÜV Rheinland, SGS, Intertek, DNV, Lloyd's Register and RINA, alongside regional and national agencies accepted by specific end users. Reputable agencies are generally accredited to ISO/IEC 17020, the international standard for the competence and impartiality of inspection bodies. Large tenders often name an approved list of agencies in the technical specification — always check whether your project restricts the choice before booking one.
Writing the inspection clause in an RFQ
To get comparable quotes, spell out in the RFQ or purchase order:
- Whether TPI is required at all, and for which items
- The approved agency, or an approved list to choose from
- The witnessing level per test stage — witness, monitor or review
- Which tests are required — hydrostatic, performance, NDT, PMI
- Who arranges and pays for the inspector's travel and fees
- The documentation format required — inspection release note (IRN/PSI certificate), test reports, data book
On the boiler feedwater pump tender we ran recently, the technical specification named a defined list of acceptable TPI agencies and required the cost of inspection to be included in the unit price for the complete lot — a good example of removing ambiguity before quotes come in, rather than negotiating it afterward.
Need TPI built into your next RFQ? Send us your equipment list and inspection requirements and we will structure the tender so every offer is quoted on the same inspection basis.
Frequently asked questions
Who pays for third-party inspection?
Normally the buyer, since TPI protects the buyer's interest — either as a separate line item in the purchase order, or built into the equipment price by the manufacturer if the RFQ specified TPI as a requirement. Always state in the RFQ who is expected to bear the cost, to keep quotes comparable.
What is the difference between TPI and a Material Test Certificate?
A Material Test Certificate (e.g. EN 10204 3.1) certifies the material itself. TPI is broader — it covers witnessing or reviewing the manufacturing and testing process as a whole, which may include reviewing material certificates as one part of a larger inspection scope covering dimensions, NDT, hydrostatic and performance testing, and final visual inspection.
Can the buyer's own engineer act as the third-party inspector?
Not really — by definition a third-party inspector is independent of both the buyer and the manufacturer. A buyer's own staff attending a factory test are usually described separately, as a customer witness or customer inspection, distinct from an accredited TPI agency's inspector.
How far in advance should TPI be arranged?
Notify the TPI agency and the manufacturer's inspection schedule as soon as the production and test dates are known — typically several weeks ahead for standard equipment, longer for complex or long-lead pumps and pressure vessels — so the inspector can be booked and travel arranged, especially for factories in remote locations.
