Brittle Failure of Valve Body Bolting on Dublok Double Block Ball Valves

A UKCS asset has revealed multiple brittle fracture failures to the body bolting on Dublok DBB valves since 2023.

None of the failures to date have resulted in process release due to the remaining bolting providing sufficient redundancy in body integrity. Had the bolting failures exceeded the available redundancy, then there is the potential for the valve body to separate completely from the body adapter and cause a full-bore release from the pipework.

Valves were in service for approximately 20 years. The valve type affected is the Modular Integral Double Block and Bleed ball valve, supplied by Dublok to many UK operators in the period 2000-2010.

Failures have been observed on a range of valve sizes and pressure ratings, up to 2500#.

All failures noted to date have been on uncoated CRA material valves where no additional paint coating was applied over the electroplated body bolting.

Visual inspection of the corroded machine screws as well as “tap-testing” them was carried out on approximately 500 valves, with multiple additional instances of brittle facture exposed.

Testing of the failed cap-head bolting showed abnormally high material hardness.

The cause of the failure was determined as hydrogen induced cracking (HIC), with the source of the hydrogen being the external corrosion of the bolting.