Twelve Two-Inch Bolts at 830 Metres

• 830 msw Water depth
• 12 × 2 in Bolts constraining the flange
• ~5 min Per cut
• One dive All cuts completed

The problem

A flange joining a flowline to a riser in the Stybarrow field, Western Australia, in 830 metres of water, had to be separated by removing the twelve two-inch bolts constraining it. DOF Subsea approached us for a tool capable of it. The FBC-300 flange bolt cutter had done the job on many previous scopes: it clamps hydraulically onto the flange, drives around it to the cut location, and cuts the bolts with either a diamond or a friction disk.

What had to change

This flange was larger than the FBC-300 design parameter, so the tool was modified to suit it. A trial was then run at the Malaga facility, which established that the modified tool would clamp onto the larger flange and cut all twelve bolts on a single disk. That trial is the reason the offshore scope was a single dive rather than a diagnosis.

Onshore trial

Ten by tool, two by rattle gun

Ten of the twelve bolts were taken with the FBC-300 and the last two with a rattle gun. Releasing the final constraint under a cutting disk gives the flowline and riser somewhere to move; the rattle gun keeps that movement controlled.

Outcome

Once clamped, the FBC-300 completed all ten cuts in the one dive, averaging five minutes per cut. It was positioned and operated by a standard work class ROV using the dirty work pack to control the clamp arms, the rotational drive and the rotation and feed of the diamond disk.

On the flange

Delivered under our former name, Proserv Australia.

Decommissioning