Repair clamps withstand 780bar pressures

Edited by the Engineeringtalk editorial team Apr 20, 2007

FurmaSeal high-pressure repair clamps are designed for rapid and economical on-line pressure leak sealing, whether subsea, topside or onshore.

FurmaSeal high-pressure self-sealing repair clamps from Furmanite, the technical services company geared to maximising asset uptime, have set a new standard in pressure leak sealing, having been shown in pressure tests to withstand pressures of a massive 780bar - believed to be a new record in pressure containment by a leak sealing clamp.

FurmaSeal high-pressure repair clamps are designed for rapid and economical on-line pressure leak sealing, whether subsea, topside or onshore.

The clamp consists of a split sleeve fitting that is installed to cover the damaged section.

It is then bolted to seat and compress the double elastomer seals around the pipe at both ends of the clamp and between the two clamp halves, and fully tensioned to the necessary pre-load.

The FurmaSeal concept can be applied in standard or bespoke designed clamps to meet specific requirements.

Cross asset clamps for instance are designed to allow pipe out-of-roundness and outside diameter variations of more than 30mm to be accommodated, thanks to a system of interchangeable inserts and seals, so that they can be held as contingency measures and applied to a number of different lines as and when the need may arise.

In this instance, the high-pressure repair clamps were being developed as contingency measures for subsea application to accommodate design pressures up to 520bar for 406 and 457mm water injection lines.

The clamps feature a double-seal arrangement to allow seal integrity to be verified following installation by pressurising the inter-seal annulus.

A number of design factors had to be taken into consideration in order to meet the required high-pressure performance.

Key among these was the design of the seal anti-extrusion system, which had to allow pressurisation of the seals (to almost 2000bar when energised) without the seal extruding into any gaps or between the bore of the clamp and the pipe.

Furmanite undertook a programme of virtual prototyping to assess and identify the appropriate design and materials combinations using finite element analysis (FEA) as standard materials and designs would not have been sufficiently strong to allow the required pressures to be achieved.

The structure stiffness was a further design consideration.

The body of the clamp would be subject to deflection under the pressure loading which, at such high-pressures, would result in the joint prising open and the seals extruding, causing pressure containment to be lost.

A high level of rigidity in the joint was therefore required.

Finite element analysis was again used to confirm that the joint would withstand the deflection and remain fully closed at the test pressure.

Given the high levels of stress to which the anti-extrusion system is subjected, materials 2.5 times the strength of standard structural steel were used.

The resulting FurmaSeal clamp, 3.3m in length and 1.8m wide, represented a total assembled mass (including bolt tensioning equipment) of some 30,000kg.

Pressure tests carried out included the interspace between the twin seals and the full cavity, and demonstrated that the clamp was capable of full pressure containment to a massive 78bar.

"This is thought to be the highest pressure containment ever achieved by a self-sealing repair clamp", Furmanite Head of Sales Mike Tucker reports.

"It demonstrates our ability to provide operators with the ability to repair high-pressure subsea leaks quickly and economically, where previously it would have been commonplace to cut and replace, involving considerable costly downtime".