When an oil and gas operator needed a pipeline valve replacement with key considerations, Curtiss-Wright EST Group proposed a solution.
Safety and speed are key considerations when a pipeline valve needs to be replaced. However, when the pipeline cannot be fully drained of its contents and depressurised, these considerations take on a whole new sense of urgency.
For an oil and gas operator working off the coast of Australia, this was the case. The operator needed to replace a blowdown valve on a spool filled with hydrocarbons on one of its offshore platforms.
They wanted to avoid the conventional process that requires flushing, purging, and then drying the entire spool volume prior to performing the changeout, all of which would add a great deal of time and money to the project.
Further complicating the process, the valve changeout had to be done while ensuring that the spool was completely isolated at all times. There could be no oxygen ingress to the line and no release of hydrocarbons into the atmosphere.
Field-proven solution
Curtiss-Wright EST Group proposed a solution that previously proved successful for the operator in other “tie-in” applications, such as installing new flanges into existing pipework: the Double Block and Bleed (DBB) Test and Isolation Plug.
The DBB is widely used to isolate and monitor potentially explosive vapors from upstream gases or hydrocarbon fluids in a vessel or pipeline during modifications or repairs requiring hot work.
The plug’s dual-cavity port creates a completely air-free, positive pressure barrier between its seals, allowing isolation for welding activities and hydrotesting of new weld connections to be performed with the same isolation tool.
Traditionally, this plug is used to increase the safety for welding activities and gives the operator the ability to hydrotest the new weld between the seals with less than 3.785L of water. This reduces fill times, wastewater, and treatment expenses while facilitating testing in remote areas of the facility.
The dual port system also allows water to be circulated between the seals for improved cooling during pre-and post-weld procedures.
The standard DBB’s seal is pressure rated to 155BarG, with upstream pressure rated to 0.7BarG. Higher pressure ratings can be achieved with special plug designs.
A novel installation approach
While the operator was confident that a standard DBB would effectively isolate the line during the valve changeout, the installation process presented some challenges. The valve would have to be opened to allow the plug to pass through to its set point, which would expose the system to oxygen.
Working in collaboration with its Australian distributor PipeServ, EST Group developed a customised plug and installation strategy, with the ultimate goal of making plug installation as efficient, seamless, and risk-free as possible, without adding to the operator’s maintenance budget.
The launching spool and DBB were designed to safely isolate the valve during changeout through the following installation process. First, the spool assembly was attached to the valve flange. Then, the DBB was inserted into the spool assembly with a lanyard and the chamber was sealed with a flange. Nitrogen gas was introduced between the flange and the DBB plug to displace all oxygen from the system.
With the launching spool closed off and no oxygen present, the valve was then opened to allow passage of the plug.
The DBB was pushed out of the launching spool assembly, through the valve and extended into the line with a long push rod to isolate the valve flange while the upstream chamber was pressurised with nitrogen.
The assembly was designed to ensure that the DBB would be positioned in the line precisely where it needed to be with a predetermined measurement verification marking on the lanyard.
The position of the plug in the line made the conventional actuation process of mechanically activating the plug by manually torquing the nuts on the shaft of the plug impossible. The system was under pressure and closed off from the atmosphere. This necessitated the special hydraulically actuated plug, which included a hydraulic piston cylinder internal to the DBB. The cylinder was activated by energising a hydraulic hose that fed to the plug.
As the cylinder moved, it compressed the seal material forming a leak-tight seal on the two locations on the pipe wall.
During deployment of the novel DBB plug, the team had to develop a way to not only extend the plug to its setting location and safely bring it back, but also maintain pressure boundaries between the hydraulic hose assembly, connections, fittings, and gauges inside the launching spool assembly and the atmosphere.
The solution was to route the hose assembly around the push rod in a spiral. As the plug was moved into position, the assembly extended like an unraveling spring to ensure service to the test plug was maintained while the plug was extended. Once the seals were compressed, the hydraulics were locked and monitored and remained in the system—along with the plug and the rod.
To ensure that the plug was fully engaged with the pipe during the entire process, the team had to continuously monitor the pressure at the plug.
The plug was positioned in the line such that the two seals straddled a 4-inch auxiliary pipe running off the main line. The team pressurised the auxiliary line and monitored it for any drops in pressure, which would indicate that one or both seals was leaking.
With the plug secure, the nitrogen pressure was released, and the launching spool assembly and failed blowdown valve were safely removed. A new valve was securely installed.
The launching spool assembly was reinstalled to the new valve flange and the process was reversed to safely remove the special DBB plug.
Success through collaboration
EST Group needed to operate under a tight timeline to ensure successful execution of this project. Working closely with the operator’s team to ensure it met all of their specifications, they were able to develop the hydraulically actuated DBB plug and successfully deliver it within the short window of opportunity.
In addition to the operator’s crew, a dedicated PipeServ technician was on site during the process to ensure the valve change-out went smoothly. The crew was able to perform the valve replacement in about one day, realising a significant cost savings in time and labor for the operator, over the four-day schedule originally planned.
The custom solution not only delivered lower repair costs versus a traditional valve replacement procedure, but the operator was able to keep their crew safe and the integrity of the pipeline and other equipment intact as well.
For more information, visit cw-estgroup.com.
This article featured in the March edition of The Australian Pipeliner.
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