API 619 vs GB/T 150: What Offshore Air Compressor Skid Buyers Need to Know Before FAT
API 619 tube compressor performance test, GB/T 150 tube pressure vessel manufacturing, the two cannot be replaced, and FAT card points are concentrated in seven intersecting areas: material certification, welding qualification, NDT ratio, pressure testing, double nameplate, third-party inspection scope, and anti-corrosion coating.
Why API 619 and GB/T 150 Are Not Interchangeable
API 619 scope: Rotary-type compressors (screw, centrifugal) for petroleum, petrochemical, and natural gas industries. Core requirements: performance guarantees, mechanical running tests, vibration and noise limits.
GB/T 150 scope: Pressure vessel design, materials, fabrication, inspection, and acceptance. (GB/T 151 covers heat exchangers.)
Key conclusion: An offshore compressor skid is simultaneously governed by both systems—the compressor is performance-tested to API 619, while the gas-liquid separator, buffer vessel, and cooler shell side are designed and fabricated to GB/T 150. The skid structure follows API 610/ISO 1461 or the project specification separately.
Procurement trap: Checking only the API 619 certificate without verifying vessel compliance will get you stuck at FAT by third-party inspection (CCS/DNV/ABS).
The 7 Cross-Check Points Before FAT
| Checkpoint 1 — Material Certification | API 619: Main pressure-bearing materials must be traceable. GB/T 150: Material quality certificates, re-test requirements, and overseas materials must comply with GB/T 150.2 annex. What to check: Verify that EN 10204 3.1/3.2 certificates cover both the vessel shell and compressor housing; for 316L stainless steel, check the PREN value. | ||
| Checkpoint 2 — Welding Procedure & Qualification | API 619: Welded rotors/housings per manufacturer standard + project specification. GB/T 150: WPS/PQR per NB/T 47014, welder qualification per TSG Z6002. What to check: Request the vessel weld WPS/PQR list before FAT and verify it covers the actual welding positions. | ||
| Checkpoint 3 — NDT Ratio | API 619: Typically does not specify vessel NDT ratios. GB/T 150: RT/UT ratios (100% or 20% spot) based on vessel category. What to check: Offshore skids are often required by owners to have 100% RT or UT, exceeding the GB/T 150 minimum—lock this down in the purchase specification in advance. | ||
| Checkpoint 4 — Pressure Test | API 619: Mechanical running test + performance test (flow, pressure ratio, power, vibration). GB/T 150: Hydraulic test at 1.25× design pressure / pneumatic test at 1.15×. What to check: Verify that test pressure, holding time, test medium, and water temperature simultaneously satisfy both documents; pneumatic testing requires additional safety approval. | ||
Checkpoint 5 — Nameplate & Documentation | API 619: Nameplate with model, flow, pressure ratio, speed, power, and API 619 mark. GB/T 150: Nameplate with design pressure, design temperature, vessel category, and supervision inspection mark. What to check: Verify dual nameplates are complete before FAT; a missing supervision inspection stamp on the vessel nameplate is a common rejection item. | ||
Checkpoint 6 — Third-Party Inspection Scope | What to check: Whether the CCS/DNV/ABS inspection scope covers the vessel fabrication process rather than only the final test; verify the H/W/R point settings in the ITP (Inspection and Test Plan). | ||
Checkpoint 7 — Coating & Corrosion Protection | What to check: Offshore environment C5-M or CX coating systems; verify the coating system (e.g., 335μm epoxy + polyurethane), adhesion test, and salt spray test reports; IP56 protection rating requires a third-party certificate. | ||
| Checkpoint | API 619 coverage | GB/T 150 coverage | Must-check documents before FAT |
| Material certificates | Partial | Complete | EN 10204 3.1/3.2 + re-test report |
| Welding qualification | Not specified | Complete | WPS/PQR + welder certificate |
| NDT ratio | Not specified | By category | RT/UT Report + ITP |
Pressure test | Performance test | Hydraulic/pneumatic | Test record + third-party witness |
Nameplate | Performance parameters | Vessel parameters + supervision | Dual nameplate photos |
Third-party inspection | Project specification | Supervision inspection | ITP + inspection report |
Coating | Project specification | Not covered | Coating report + IP56 certificate |
Case Data: What a Real Offshore Skid FAT Revealed
Real parameters of FAT for CNOOC project (partially disclosed)：
Model: Customized Screw Air Compressor Skid
Key parameters: -40°C dew point, 316L stainless steel corrosion protection, IP56 protection, IE4 motor efficiency, CCS certification
Items actually scrutinized during FAT: vessel weld NDT reports, pneumatic test records, dual nameplates, coating adhesion, vibration values
Conclusion sentence: Whether FAT passes often does not depend on compressor performance, but on whether the vessel and skid system documentation is closed-loop complete.
FAQ
Q1: Is API 619 mandatory for offshore air compressor skids?
It depends on the project specification and owner standards. API 619 is the industry benchmark for rotary compressor performance and testing, but offshore projects typically reference API 619 + GB/T 150 + project specification simultaneously, applying the stricter of the three.
Q2: Can a GB/T 150 vessel be used in an API 619 compressor package?
Yes, but the purchase specification must explicitly state that the vessel is designed and fabricated to GB/T 150 while the compressor is tested to API 619, and cross-witness points must be set in the ITP.
Q3: What documents should be ready before FAT?
Material certificates, WPS/PQR, NDT reports, pressure test records, dual nameplates, coating reports, IP56 certificates, signed ITP, and vibration/performance test records.
Q4: Does CCS certification cover both compressor and pressure vessel?
The CCS inspection scope must be defined in the contract. It usually covers the skid as a whole, but vessel supervision inspection may be performed by the local special equipment inspection institute. The coverage boundaries of both certificates must be verified.