Knutsford-based subsea valve specialist Oliver Valvetek, in conjunction with a major oil and gas operator, a subsea tree manufacturer and a subsea tooling company, has developed a receptacle for operation by a remote operated vehicle (ROV) that will protect subsea valves from damage caused by the accidental application of too much torque.
“The problems arise because Class 4 ROV receptacles have to be designed in accordance to API 17D / ISO 13628-8. This allows for a maximum operating torque of 2,711Nm, which is considerably higher than the torque to damage limit of subsea valves,” explained Paul Shillito, engineering director.
The torque applied to subsea hardware can be set by the ROV operator, however if this setting is not accurate then in theory the ROV can apply a torque far greater than the valve can tolerate.
“Historically the operators have used different class receptacles for different duties but this requires the tooling to be changed, which means bringing the ROV to the surface and, of course, carries an associated cost in terms of downtime,” said Mr Shillito.
To combat both the problem of damage caused by excessive levels of torque and that of costly topside retooling, Oliver Valvetek has developed a receptacle with an integral shear pin that is set to a level slightly below the torque to damage figure of the valve.
“The shear pin is housed in a retrievable cartridge that is located in the receptacle and operated via a traditional Class 4 square drive mechanism,” said Mr Shillito. “If the valve is over-torqued then the shear pin is designed to snap before the valve can become damaged.”
“In this eventuality a special tool has been developed that allows the ROV to remove the cartridge and replace it with a new one housing another shear pin. All this can be done with the valve remaining in-situ on the seabed.”
The cartridge is held in place by an O-ring, which fits into a groove in the receptacle.
“We’ve had to develop the geometry of the O-ring groove and run tensile tests. If the configuration is too weak then the cartridge would simply fall out, but if it is too strong then the ROV may not be able to retrieve it.”
“In the past we have seen instances where operators have accidentally broken the spindles of needle valves on tree installations, resulting in the tree being shut down whilst the valve is replaced. With this system, it simply cannot happen.”