October 2017


Subsea Pipeline Repair

Although pipelines are accepted as a safe form of energy transportation, failures can and do occur. Damage sustained to a submarine pipe in particular, can prove challenging to repair. As identified in DNV GL RP F113 Subsea Pipeline Repair, the main cause of pipeline damage is caused by a degradation mechanism such as corrosion, Hydrogen induced stress cracking (HISC) or physical damage such as unstable seabed conditions, anchor strike, dropped objects and trawl gear interference. In cases where pipeline damage has occurred, the damaged section may need to be cut from the pipeline and replaced with a new pipe section. STATS has developed a range of subsea line stop equipment to allow the safe isolation and access to the pipeline without the need for de-pressurisation or flooding. With the addition of a bypass line, pipeline repairs can be completed with no interruption to pipeline production. As well as pipeline repair, the subsea BISEP® can be used to temporary isolation subsea pipelines to allow critical valve replacement or the tie-in of pipelines.

Illustration of typical subsea pipeline repair scenario

Subsea BISEP® – Hot Tap and Plugging

The subsea BISEP® provides the highest level of hot tap installed pipeline isolation in the industry and complies with subsea isolation guidelines, ensuring safe worksite conditions for divers during breaking of containment activities. The BISEP® is the only hot tap installed double block isolation tool that satisfies the design criteria for DNV GL type approval for Pipeline Isolation Plugs. The design criteria satisfies the requirements for Pipeline Isolation Plugs to provide dual seal and isolation in accordance with Offshore Standards; DNV-OS-F101 (Submarine Pipeline Systems) and recommended Practices; DNV-RP-F113 (Subsea Pipeline Repair) and in compliance with the following code; ASME BPVC Section VIII, Division 2.


Traditionally, hot tap installed line stop isolation tooling provides only a single passive barrier, which is neither testable nor monitorable. As the isolation cannot be guaranteed, additional hot tapped vent ports are required to be installed after the seal to vent any pipeline contents that may pass the seal. To increase safety, secondary line stop isolations may be installed. This approach has negative implications for operators, increasing subsea hot tapping operations and fittings on the line, increasing costs and extending scope duration. 

Left- 14” Subsea BISEP® deployment. Right- Hot tap machine and fitting deployment.

Fail-safe Double Block and Bleed Isolation

STATS patented BISEP® provides fail-safe double block and bleed isolation deployed through a single full bore hot tap penetration, without the need for additional bleed or vent ports. The BISEP® offers significant safety advantages over traditional line stop technology, the hydraulically activated dual seals provide leak-tight isolation of live, pressurised pipelines. This high integrity isolation is provided by a spherical dual seal plug which is deployed from a pressure competent launcher through an isolation valve and rotated towards the flow of pressure to be isolated.

3D image showing BISEP® set with dual seals providing leak-tight isolation.

The seals are activated by a hydraulic cylinder inside the plug which compresses the seals, the resultant radial expansion pushes the seals out against the pipe bore. Further application of hydraulic pressure generates a rubber pressure in the seal elements, giving a high integrity leak-tight seal in mature, corroded pipelines. Each seal is independently tested with full pipeline pressure in the correct direction to verify leak-tight isolation. The seal annulus void is vented to ambient through the BISEP® plugging head to provide a zero-energy zone and provides constant monitoring capabilities to prove the seal integrity before and during subsea activities. Line pressure acting against the BISEP® maintains seal pressure creating a fail-safe feature providing actuation independent of the hydraulic system. In addition, the BISEP® is designed to resist back pressure so can be used as a test boundary for the reinstatement test, unlike any product on the market.

Safety of Personnel, Infrastructure and Environment

The introduction of the BISEP® to the subsea market will revolutionise how subsea hot tap installed isolations are conducted, providing true double block and bleed isolation to the market that provides the highest level of safety for divers and protection to the environment.  

As standards regarding the safety of personnel, infrastructure and the environment increases across the industry, the demand for the subsea BISEP® will continue to grow. The ability to provide high integrity, temporary isolation barriers offer operators significant benefits. Lengthy decommissioning and recommissioning of entire subsea pipelines is minimised or eliminated, increasing safety, reducing out of service time and loss of revenue.

The use of the subsea BISEP® allows isolation and repair of damaged subsea infrastructure without the requirement to depressurising or flood the entire pipeline. This approach allows repairs to be safely and efficiently conducted in some cases while production continues through a bypass.

Hot Tap and Plugging Subsea Applications

·         Mid-section pipeline repair or replacement (corrosion / mechanical impact).

·         Pipeline re-routing or platform decommissioning.

·         Isolation of pipeline end manifolds, pipeline end terminals, subsea manifolds or skids for repair, upgrade or replacement.

Hot Tap and Plugging Operator Benefits

·         Fully verified Double Block and Bleed isolation through a single hot tap penetration.

·         Leak-tight isolation dramatically increases safety over traditional line stop technology.

·         Single operation significantly reduces timescales and costs.

·         Single fitting allows installation on short sections of pipework.

·         BISEP® technology complies with operator double block and bleed requirements.

·         Minimal production disruption on interconnected pipeline networks during valve repairs / tie-ins.

BISEP® Key Features

·         Dual seal annulus void proves and monitors the seal integrity before and during any intervention work.

·         Constant monitoring of key BISEP® parameters from the vessel

·         Isolation integrity continuously monitored through annulus void, hydraulic set circuit and body vents.

·         Seal annulus void provides a zero-energy zone.

·         Design provides axial restraint through bearing on dual clevis plates (no single point failure).

·         Dual compression seals are more compliant and have a far higher success rate than traditional cup seals particularly in pitted pipework.

·         Self-energisation of seals maintains isolation integrity independent of hydraulic control circuit.

·         No need for additional taps for bleed / vent ports.

·         Can accommodate reinstatement pressure test against rear of BISEP®.

·         BISEP® isolation installed upstream of fitting, maintaining fitting in safe zone during workscope.

·         BISEP® launcher ported to facilitate venting, purging and flushing of isolated section.


·         Size range: 3” to 48”

·         Pressure range: up to 153 bar

·         DNV GL Type Approval

·         Design allows for deployment into flow conditions (Engineering Assessment Required)

Equipment Supply

To complement the BISEP®, STATS can supply mechanical hot tap fittings, patented dual seal slab valves and hot tapping machines. Once the BISEP® is recovered, STATS can provide a completion plug to provide permanent isolation to the branched hot tap fitting which enables the removal of the slab valve allowing a blind flange to be fitted.

Read some of subsea BISEP®case studies here.

Tel: +44 (0) 1224 772461