TRELLEBORG OFFSHORE, A part of Trelleborg Engineered Systems, has teamed up with First Subsea, another leading supplier to the offshore oil and gas industry, to develop a diverless bend stiffener connector – DBSC.
This provides a safe and reliable solution to the challenging problem of how to install crucial bend stiffeners without risking the lives of divers and also minimising weather interruptions.
Bend stiffeners are used to support flexible pipes, usually known as risers, or cables that run from floating oil and gas platforms at the surface down to the seabed.
The bend stiffeners are fixed to the end of the tube through which the riser runs out beneath the platform.
Made of polyurethane, the bend stiffeners restrict the movement of the riser or cable. They are essential in reducing the fatigue that risers would suffer if left swinging free in the current to bang into the mouth of the tubes they run through.
“If a bend stiffener fails, it can reduce the life of a cable by a factor of 20 or more,” says Antony Croston, Senior Design Engineer for Trelleborg Offshore.
Problems usually arise when bend stiffeners need to be fixed to tubes situated at somewhat greater depths, an operation traditionally performed by divers.
“The operation is hazardous as well as time-consuming and subject to weather interruptions,” says First Subsea Business Development Manager Paul Hughes.
Oil companies such as BP and Shell were becoming increasingly unhappy with using traditional methods, specifically divers. So Trelleborg Offshore decided to develop a diverless solution and began looking for a partner.
“We saw that First Subsea had a good track record and a trusted solution in a similar application, so we went to them,” says Croston.
The solution developed by the partners works on the principle of a connector/receptacle connection. The connector is pulled up into the receptacle of the tube. To accomplish this, the connector with the bend stiffener bolted to it is lowered into the sea and attached to the riser or cable that passes through the tube. The riser is then pulled up into the tube, taking the connector with it.
When the connector is fully inserted, it engages with the tube, releasing the attachment to the riser. This simple underwater operation is performed by a remotely operated vehicle (ROV) – an unmanned submarine.
“Not only is safety improved,” says Hughes, “but the operation can be performed in a matter of hours, instead of the days required when using a diver.
“A unique feature is that this connector can be fitted to all existing tubes. We don’t know of any other supplier that can do that.” It was oil giant BP that first decided to install a DBSC – on its Horn Mountain platform, situated in deep waters in the Gulf of Mexico.
“A vast amount of development and testing took place, as BP thoroughly examined our solution,” says Croston. “This was good for the development. If you can satisfy BP, you can satisfy most people.”
”A second order for four DBSCs is due to be delivered to the Neptune LNG Deepwater Port Terminal off the coast of Massachusetts in the United States.”
“For Trelleborg Offshore, the No. 1 supplier of bend stiffeners, finding a reliable solution was crucial.”
“We’ve got an outstanding track record in reliability and expertise for our bend stiffeners,” explains Croston. “It’s very important to protect this.”