During our inspection of valve, we found the following typical quality problem in inspected valves.
In order to reduce cost, we found some thickness of valve was not qualified. the reason was vendor choose WT thicker valve body billet in production.
The thread stroke connection of bonnet and body of needle valve was too short, the thread pre-tightening force was insufficient, the bonnet will fall off during high closure pressure test.
Pitting and blowhole was found in casting valve. Also we found sealing face damage.
4) Pressure test
During the pressure test, the leak point was often found in packing, back seat, connection of bonnet, sealing face and penetration defect in valve body.
5) Material replacement
Stem should used SS material, but carbon steel was used instead especially used in required torque Large diameter valve by some vendors.
Alloy steel should be used in valve body, but it was replaced by carbon steel (WCB) especially in anti-corrosion, sulfur resistance valve.
Copper alloy should be used in Stem nut, but some vendor used casting iron instead.