Why conduct valve inspections before shipment?
1. Stop unexpected breakdowns at customer site. Valves work within fluid pipeline systems. Bad sealing or body cracks will lead to leakage and safety hazards once put into service. Sending defective goods overseas brings huge costs for return and repair.
2. Prevent project delays. Most valves are supplied for engineering projects. Defective units hold up site installation and give rise to compensation disputes between buyer and supplier.
3. Make sure technical parameters match purchase requirements. Check body material, pressure class and connection type to avoid wrong‑material delivery.
4. Check protective packing. Valve threads and flanges get damaged easily during sea transit. Proper packing check cuts loss caused by bump and rust.
Inspection Standards
Sampling rule
Adopt GB/T2828.1, normal inspection, inspection level II
‑ Critical defect (Class A): **AQL=0**. One single unit found will reject the whole batch.
‑ Major functional / dimensional defect (Class B): **AQL=2.5**
‑ Minor cosmetic & packing defect (Class C): **AQL=4.0**
Buyer drawing, API 598 or ISO 5208 takes precedence over general rules.
Inspection items & acceptance criteria
1. Document and nameplate check (Class B)
Model, pressure rating, material grade and heat number shall match purchase order and material certificate. Markings shall be clear without missing or wrong stamps.
2. Visual inspection for valve body (Class A/B/C)
‑ Class A: Crack or penetrating sand hole on body or bonnet → batch rejection.
‑ Class B: Dent or crush on flange face and thread which harms assembly and sealing performance.
‑ Class C: Light scratch, slight surface rust and leftover burrs are acceptable if function stays unaffected.
3. Dimensional measurement (Class B)
Check flange outer diameter, bolt circle, face‑to‑face length and thread size. Out‑of‑tolerance on critical dimensions counts as major defect.
4. Opening & closing operation test (Class B)
Valve shall move without sticking or loose parts, stop at correct position. Handwheel and actuator shall be tightly mounted.
5. Hydrostatic shell & seat sealing test (Class A, carried out on client's request)
Shell test under 1.5 times nominal pressure, zero leakage during holding period. No visible leakage when valve is fully closed. Any leakage is treated as critical defect.
6. Spare parts and accessories (Class C)
Bolts, gaskets and manuals shall be complete with correct specification.
7. Packing protection and shipping marks (Class C)
Protective caps fitted for threads and flanges. Anti‑rust treatment applied on metal surfaces. Outer carton solid, shipping marks and batch labels complete.
Final judgement
1. Whole batch fails if any Class A defect appears.
2. Batch is rejected when Class B defects exceed acceptance number of AQL 2.5.
3. Batch is rejected when Class C defects exceed acceptance number of AQL 4.0.
4. Re‑inspection is allowed after supplier sorts out all non‑conforming items.
