Mechanical isolation tool for ESD valve servicing under development. [Emergency Shut Down]

Journal Article · Mon Oct 10 04:00:00 EDT 1994 · Oil and Gas Journal; (United States)

OSTI ID:6847072

Davies, R ^[1]; Maltby, T ^[2]

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1. Mobil North Sea Ltd., Aberdeen (United Kingdom)
2. Andrew Palmer and Associates, Aberdeen (United Kingdom)

Following the 1988 Piper Alpha disaster and recommendations of the subsequent Cullen report, all offshore pipelines operating in the UK North Sea must be fitted with ESD valves that are maintained in good working order. Although most ESD valves are relatively new, their maintenance is a concern to operators. During any repairs of long trunk-lines, it is desirable to maintain pressure in the pipeline to avoid venting the line. The 30-in. SAGE (Scottish Area Gas Evacuation) gas trunkline is approximately 325 km long and exports gas from the Beryl Alpha platform to the St. Fergus terminal. During a 1993 field shut-down, it was necessary to carry out major remedial works on the SAGE pipeline ESD valve as a result of unexpectedly high leakage across the valve during the statutory annual SI 1029 test. Original plans called for use of the subsea isolation valves to isolate the ESD valve during repairs. Initial testing of the valves, however, made clear that a suitable block and bleed could not be established and that alternative isolation was required. Mobil North Sea used a freeze plug. The SSIV provided a primary barrier, with the freeze plug providing the secondary barrier. The bleed between the two barriers was achieved with a surface vent from the SSIV. The paper describes the freeze-plug isolation, its performance, mechanical isolation tools, tool operation, and remote control systems.

• OSTI ID: 6847072
• Journal Information: Oil and Gas Journal; (United States), Journal Name: Oil and Gas Journal; (United States) Vol. 92:41; ISSN OIGJAV; ISSN 0030-1388
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
032000* -- Natural Gas-- Transport
Handling
& Storage
CONTROL
CONTROL EQUIPMENT
CRYOGENIC FLUIDS
EMERGENCY PLANS
ENERGY SYSTEMS
EQUIPMENT
FLOW BLOCKAGE
FLOW REGULATORS
FLUIDS
FREEZING
MAINTENANCE
NATURAL GAS DISTRIBUTION SYSTEMS
PIPELINES
REMOTE CONTROL
TECHNOLOGY ASSESSMENT
TOOLS
UNDERWATER OPERATIONS
VALVES