Valve Replacement White Paperkylesalomon Wed, 08/19/2026 - 15:35

Reduce offshore valve replacement downtime with double block and monitor isolation

Non-intrusive double block and monitor isolation technology reduces downtime, product loss, and maintenance cost.

Identify challenges driving offshore valve repair and replacement

As a natural result of use and the unavoidable deterioration of seal material over time, the repair or replacement of valves on offshore natural gas platforms is inevitable.

Often, the need for repair or replacement is identified through planned inspection and testing. Sometimes, however, a valve failure is only discovered when a leak is indicated on platform sensors.

Various types of valves serving different purposes are installed on offshore platforms, including:

Trap valves: Isolate the launcher and receiver during operations involving the loading or retrieving of pigs, inspection tools, or isolation tools, and keep personnel from being exposed to pipeline content.
Shutdown valves, including Emergency Shut Down Valves (ESDV): Actuated valves connected to the platform’s control system, allowing a safe and efficient shut down of production if a dangerous situation is detected or in the event of an incident. These valves may generally be installed topside, in the platform riser, or in the pipeline at sea bottom in close proximity to the platform.
Subsea isolation valves (SSIV): Actuated ball valves or mechanical non-return (clapper) valves that are installed on the seabed in close proximity to the platform.
Topside piping, valves, and instrumentation: Connected to the main export or import pipeline.

Regardless of the type of valve or its application, replacing it will involve complete removal of the old before installation of the new unit. Repairing in situ may only require taking it apart. Before this work can commence, the pressure and pipeline content (normally hydrocarbons) must be removed from the pipeline or section where the faulty valve is. This can be done by either decommissioning (bleeding down) the entire pipeline and then recommissioning (refilling and restoring pressure) after the work is completed, or by isolating the section where the valve will be repaired or replaced. Depressurization can be costly as valuable production is lost (pipeline inventory plus loss of production during the extended period of time required to depressurize the pipeline). Moreover, the removal of pipeline inventory can create significant environmental challenges, which further escalate the overall costs and complexities of the repair or replacement process.

An alternative to depressurization of the entire pipeline is isolation of the section on which the valve repair or replacement is to be carried out. Localized pipeline isolation offers several advantages as both production downtime and loss of pipeline product are kept to a minimum, with associated environmental and economic benefits. A wide range of methodologies, both intrusive (such as hot tapping and plugging) and non-intrusive (inline plugs, use of inline valves), can be used to isolate pressurized pipeline sections. Both intrusive and non-intrusive methods are well accepted in the industry, with the choice of one over the other being largely governed by factors such as location and accessibility of the pipeline, operating pressures, pipeline inventory, etc.

This paper outlines how non-intrusive double block and monitor plugging technology provides a double barrier isolation for gas export lines during valve replacement, satisfying regulatory requirements and operators’ concerns about safety, time, and cost.

The term “double barrier isolation” is commonly used to refer to an arrangement of two seals in series to isolate a pipeline. In general, barriers are termed double when each can retain the full pressure alone; each is tested; their integrity can be monitored; and they are “independent” of each other. The underlying requirement for a successful double barrier is therefore a system in which the failure of any one seal will not compromise the integrity of the other.

Implement double barrier pipeline isolation to improve worker safety

During pipe repair work where isolation methods are employed, establishing double barriers to safeguard personnel is often required. According to the International Marine Contractors Association (IMCA) D 044 Guidelines for Isolation and Intervention: Diver Access to Subsea Systems, use of double barriers is recommended in all situations where the failure of one barrier may be harmful to personnel:
“For subsea liquid and gas conveying equipment, the general principle is that a minimum of two independent and tested isolations should be established between personnel engaged in any task where the presence of potential hazard from a positive or negative pressure source exists.”

Double barriers for isolating pressurized pipelines can be provided through different arrangements of pipeline valves, flanges, plates, etc., or through the use of inline isolation tools that can seal against the inner wall of a pipeline. The choice of methodology is largely based on detailed risk assessment to ensure that the severity and mitigation of risks are correctly identified and measured. Double block and bleed (DBB), double isolate and bleed (DIB), and double block and monitor (DBM) are commonly used arrangements for providing double barriers in pressurized pipelines.

DBM is the principle incorporated into the design of the SmartPlug® pipeline pressure isolation tool, which features two independent plug modules in its standard configuration. This allows the integrity of each seal to be validated at all times by monitoring the pressure in the annulus (between the two plug modules), which represents a significant safety advantage.

The DBM isolation technology behind the SmartPlug tool has been evaluated by Det Norske Veritas Germanischer Lloyds (DNV GL), one of the leading technical assurance, advisory, and risk management companies in the global oil and gas industry, and has been found to satisfy the Safety Class requirements specified in DNV-RP-F113.

Deploy double block and monitor isolation for safer offshore operations

The proprietary SmartPlug tool is a non-intrusive, double block and monitor pipeline pressure isolation solution
that allows any pipeline section to be isolated at, or close to, operating pressure. The modular, self-lock, double block design ensures fail-safe operations in most pipeline media, including gas, crude oil, distillates, treated/untreated water, glycol, and diesel. Articulated modules increase piggability of the bi-directional tool. The standard tool configuration consists of two independent plug modules. These typically travel on a spring loaded wheel system. Each is independently capable of isolating the full pipeline pressure, thus providing a true double-block isolation anywhere in the pipeline system. In some cases, a third plugging module is added for post-repair hydrotesting, using the same tool without retrieving it from the pipeline.

A typical isolation tool has one pig module on each end. These house the onboard control and communication system and assist in driving the tool in and out of the pipeline. The control and communication system communicates wirelessly with the external extremely low frequency (ELF) antenna placed on or above the pipeline.

The standard SmartPlug tool is designed to seal against 250 bar (3,000 psi) operating pressure. The control module (CM) contains the communication and pressure monitoring capabilities, a tracking system interface, battery pack, hydraulic system, and means of contingency unsetting of the tool. The monitoring and tracking module (MTM) is outfitted with a backup pressure monitoring and tracking system together with a battery pack. The MTM may be outfitted with an additional method for contingency unsetting of the tool independent of the CM. Each plug module is designed and tested to seal against the full pipeline differential pressure. The design provides th...

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Reduce offshore valve replacement downtime with double block and monitor isolation

Identify challenges driving offshore valve repair and replacement

Implement double barrier pipeline isolation to improve worker safety

Deploy double block and monitor isolation for safer offshore operations

T.D. Williamson

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