48" BISEP, Precision Pipeline Intervention, Gas Segregation, Oman

When OQ Gas Networks needed to integrate a new extension of Sur gas supply station into their existing 48" pipeline, the connection point was on a live, pressurised system serving customers continuously. Shutting down and purging the entire 65km pipeline was not a viable option - the disruption to gas supply, and the greenhouse gas emissions from large-scale venting and flaring, made it unacceptable. The work had to be done with the pipeline in service.

STATS was contracted to perform hot tapping and line stopping operations on the 48" pipeline in Sur, Sultanate of Oman. The scope involved deploying dual BISEP line stop tools to create a verified, leak-tight double block and bleed isolation of a 150-metre section - isolating it for modification while gas continued flowing to OQGN customers through an integrated bypass.

The 48" pipeline runs 65 kilometres and supplies gas to OQGN customers without interruption. Integrating the new Sur gas supply station extension required modifying a 150-metre section of that live pipeline - welding fittings, making connections, and removing existing pipe spools - while the rest of the system remained pressurised and in service.

A full pipeline shutdown would have required purging and venting the entire 65km line before any work could begin, then recommissioning it afterwards. Beyond the cost and service disruption, the associated greenhouse gas emissions from venting and flaring at scale made that approach unacceptable. The project required a method of isolating only the section under modification, with gas continuing to flow around it.

STATS deployed two 48" BISEPs - one at each end of the 150-metre section to be modified. Each BISEP was introduced through a full bore hot tap intervention: a split tee fitting welded and hydrotested on the pipeline, a slab valve and SureTap hot tap machine installed, a hot tap made and the coupon recovered, and the BISEP deployed through the resulting full bore access point.

With both BISEPs set, a 150-metre temporary bypass line was constructed between the two deployment launchers, operating at 75 bar to carry gas flow around the isolated section throughout the workscope. Each BISEP features dual elastomer seals hydraulically compressed against the pipe wall. Hydraulic activation provides high-integrity sealing even in pipelines with internal corrosion, pitting, or ovality. Once set, each BISEP was tested at full pipeline operating pressure - with each seal independently pressure tested in the correct direction. The annulus between the seals was vented to create a zero-energy zone, which was monitored continuously throughout the operation.

Only when the independent test regime was complete and an Isolation Certificate issued did work on the isolated section begin.

The BISEP is the only DNV Type Approved line stop tool, verified against DNV-OS-F101 (Submarine Pipeline Systems), DNV-RP-F113 (Subsea Pipeline Repair), and ASME BPVC Section VIII, Division 2 - confirming its design meets the requirements for dual seal and isolation of pressurised pipeline infrastructure.

With the isolation confirmed and the certificate in place, STATS supplied a mechanical strap clamp with a 2" branched off-take to provide a controlled vent point on the isolated section. A hot tap machine and valve were installed and the pipeline drilled. The isolated 150-metre section was safely flared and nitrogen-purged until gas-free conditions were confirmed.

Cold cutting machines were then used to remove sections of pipe spools from each end of the isolated section. A tie-in pipeline bend spool was precisely positioned and welded into place at both locations to provide the connections for the Sur gas supply station extension.

With tie-ins complete and the extension commissioned by introducing gas, the isolation certificates were withdrawn. Both BISEPs were gradually unset and retracted into their deployment launchers. The slab valves were closed and the BISEPs recovered. The hot tap machines were reinstalled onto the slab valves and used to install 48" completion plugs into the split tee fittings, providing secure, permanent blinding of the intervention points.

The integration of the Sur gas supply station extension into the existing 48" pipeline was completed without disrupting service to OQGN customers. Gas flow was maintained continuously throughout. The 65km pipeline never went offline.

By avoiding a full pipeline shutdown and purge, the project significantly reduced greenhouse gas emissions compared with a conventional approach. For operators on large-scale gas transmission infrastructure, this project demonstrates what is achievable with a verified, monitored isolation and the right equipment - modifications on a live, pressurised system, carried out safely, without the cost, disruption, or environmental impact of a full-line shutdown.