BISEP, High Temperature Steam Line Isolation Rehabilitation

The BISEP's standard elastomer seals are rated to 150 degrees Celsius. The steam lines at this Middle East refinery ran at up to 381 degrees. That gap - more than 230 degrees beyond the tool's certified operating range - was the central problem STATS had to solve before a single hot tap could be made.

STATS had been contracted to provide leak-tight pipeline isolation services on three pressurised steam lines as part of a wider restoration project at a major refinery following a fire. The project would ultimately involve 48 individual hot tap and BISEP line stop deployments and 24 Tecno Plug isolations - ranging from 2" to 54" in diameter - all completed in nine months. But before any of that could happen, STATS had to prove that a tool could work in conditions it had never been certified for.

The three steam lines to be isolated - a 30" x 30", a 24" x 6", and a 36" x 10" - were operating at temperatures between 190 and 381 degrees Celsius and pressures between 4 and 42 Bar. Standard BISEP technology uses HNBR (Hydrogenated Nitrile Butadiene Rubber) elastomer seals, which are qualified to a maximum of 150 degrees. Deploying them into lines running at more than twice that temperature was not an option.

The pipework added further constraints. None of the lines were piggable, which ruled out any inline deployment approach and meant STATS had to access each isolation point through a branched fitting - either a welded split tee or a mechanical hot tap clamp - with equal-sized branches to allow hot tapping and BISEP deployment into the live steam.

The steam pipework was located 20 metres above ground level, with limited working space due to surrounding pipework. Scaffolding had to be erected at each isolation location. Working at that height in close proximity to pipelines radiating intense heat required a detailed risk assessment for every isolation point - workers in safety harnesses, heat protection suits, reduced shift patterns, and regular crew changes throughout all live activities.

STATS explored both elastomer and graphite seal options to find a material capable of providing a leak-tight seal at 381 degrees and 42 Bar. To test candidates, STATS constructed a dedicated 10" test fixture at their operational facility in Abu Dhabi - attaching heat blankets to a canned-end fixture to replicate the extreme temperature conditions - and ran multiple prototype deployments to evaluate graphite and rubber seal performance under load.

After extensive testing, two materials proved capable of sealing at the required conditions: a graphite seal and a specialist high-temperature rubber compound. STATS selected the specialist rubber seal for the project based on its performance during testing. Before committing to live deployment, STATS conducted final validation tests at the refinery itself using a 10" steam loop - providing confirmation that the rubber compound would perform as required at the actual temperature, pressure, and flow conditions of the live pipelines.

With a qualified seal material in hand, STATS developed an isolation methodology that used the physics of steam to make the deployment of a standard BISEP possible - even in lines far beyond its rated temperature range.

STATS identified the u-bends in the steam system as the optimal isolation locations. A modified BISEP fitted with a single high-temperature seal was deployed into the steam line at the u-bend location to create an initial heat barrier. Once the modified BISEP was set and the flow of steam arrested, condensation began to form behind the isolation point. The u-bend gradually filled with water, which cooled the section of line behind the barrier from 381 degrees down to a temperature at which standard seals could safely operate.

With the line cooled and water-filled behind the heat barrier, a standard HNBR dual-seal BISEP was deployed into the line behind the modified BISEP. Each seal was independently pressure tested and the annulus between them vented to atmosphere - creating a fully monitored, leak-tight double block and bleed isolation. An isolation certificate was issued to the client, permitting breaking of containment to proceed safely.

The client required that the hot tap clamps and fittings be removed from the pipeline after the work was complete - leaving no permanent fittings on the line and eliminating any future integrity risk from additional leak paths. With the BISEP still providing a monitored isolation barrier, a pressure-competent temporary launcher was installed to the cut pipe end, with a pre-installed Tecno Plug fitted with high-temperature HNBR dual seals inside. The Tecno Plug was deployed through the launcher and positioned upstream of the BISEP, then hydraulically activated to set locks and seals and create a zero-energy zone between the seals. Once the Tecno Plug was confirmed leak-tight and providing the primary isolation, the BISEP was unset, retracted, and recovered. The clamp and fitting were then safely cut from the pipeline, a flange welded onto the pipe end, and a full-bore valve installed - leaving the pipeline ready to return to service with no residual fittings.

In total, STATS completed 48 individual hot tap and BISEP line stop deployments and 24 Tecno Plug inline isolations - covering steam and hydrocarbon pipelines ranging from 2" to 54" in diameter. Design, manufacturing, and all onsite activities were completed within nine months.

To the best of the company's knowledge, this project represents the world's first successful temporary double block and bleed line stop on large-diameter live steam pipelines - a benchmark achieved through original research and development, rigorous prototype testing, and a two-stage isolation methodology engineered specifically for the thermal conditions of the steam system.

When the temperature gap between a client's requirement and a tool's rated capability is more than 230 degrees, the answer is not a workaround - it is original engineering. STATS developed new seal materials from scratch, built a test facility to qualify them, validated the solution at the refinery before going live, and designed an isolation methodology that used the thermodynamic behaviour of steam to extend the tool's operating envelope safely. The result was not just a completed project - it was a proven capability that now exists where none did before.