When it comes to pipelines, safety is non-negotiable, which is why T.D. Williamson’s ProStopp® DS is a leading tool in pipeline isolation.
No matter where its operated or which products pipelines carry, integrity is non-negotiable. And while that’s true for the entire industry, gas distribution operators face elevated stakes. After all, when a pipeline literally runs through someone’s backyard, any failure can have enormous consequences.
As the gas distribution industry has grown and regulatory requirements have increased, the technology for keeping systems running safely has advanced to keep pace.
And the effort has paid off: Australian pipelines have a strong safety record and operators know how to effectively manage risk during operations, maintenance and repair. That includes safely isolating their pipelines to create secure work zones without interrupting service to customers.
For decades, gas distribution operators worldwide have successfully isolated their pipelines using a plugging system equipped with a rigid rubber, or static seal.
The SHORTSTOPP® plugging system, for example, meets industry standards for isolating gas distribution mains and is compatible with pipelines operating at pressures up to 35 bar (500 psi).
In 2020, T.D. Williamson (TDW) introduced a new isolation tool, the ProStopp DS, that brought the security of double block and bleed technology to the gas distribution industry and features an energised, or expandable, plugging seal designed especially for low-pressure lines.
The tool also features an integrated chip sweep attachment that removes excess cutter shavings from the sealing area that could otherwise interfere with the sealing performance.
The advantage of the energised malleable rubber seal is that it can expand outward to adhere to the internal topography of the pipe, even if there are geometric anomalies like dents, gouges or irregular weld seams.
Or, in an exceptionally rare but real-life example, when corrosion coating has built up, hardened and become uneven over time. In this case, the corrosion coating created an internal diameter surface condition that would have been more challenging to seal using rigid technology, meaning shutdown might be required before the operators could proceed with their work.
Complexity in overdrive
TDW technicians always prepare for the unexpected, and it’s rare when something surprises them.
Between training under rigorous field conditions and years of experience, they’ve seen just about everything, and they know how to mitigate risk and protect people, assets and the environment.
But when hot tapping and plugging crews arrived at the worksite where they would be isolating a 10-inch (25.4 cm) gas distribution pipeline before rerouting, they had no reason to expect the job would be out-of-the-ordinary.
They certainly didn’t think there would be anything abnormal about the 0.375-inch-thick (0.9 cm) pipe wall.
Once they cut into the coupon to allow access into the pipeline, though, they immediately saw that something was not right. Instead of the pipe wall being smooth and uniform, it was covered with a thick substance that appeared to have passages cut through it.
This was likely the residue of an asphalt/tar coating. Even more concerning, however, was that more than an inch (2.54 cm) of anti-corrosion coating had pooled and hardened at the bottom of the pipeline interior, introducing ovality that could make isolation with a rigid seal more challenging.
Since the ProStopp DS tool’s energised seal is effective on irregular surfaces, the TDW field team knew it would be an appropriate choice for this tricky isolation. In fact, it was the only option for isolating a pipeline with such challenging surface conditions.
To ensure success, the crew contacted the TDW Applications Engineering team, a group of experienced technology professionals who understand every aspect of the design and operation of every valve, fitting, isolation plug and drilling and tapping machine in the TDW portfolio.
Application engineers are empowered to innovate and qualified to modify equipment to perform safely and effectively, even under the most extreme circumstances. In other words, they create inventive solutions that field technicians can actually accomplish. They also support on-site teams every step of the way.
Engineers advised the technicians to begin the isolation by expanding the plugging heads at standard hydraulic pressure and then incrementally increase the hydraulic operating pressure until it reached the maximum.
This would exert more force to compress the sealing elements against the pipeline’s rocky walls. The technician energised the plugging heads, and the operator blew down the isolated section.
More confident sealing wasn’t the only reason using ProStopp DS technology made sense. Its double block and bleed capabilities helped overcome complex challenges related to hidden leak pathways.
Unconventional solution
After setting the ProStopp DS, the lower explosive limit (LEL) sensors monitoring for gas leakage detected a leak downstream of the plugging heads.
Because ProStopp DS technology is engineered so any product between the primary and secondary plugging head is safely bled off through a port, TDW engineers knew that’s not where the gas leak was coming from. They theorised the gas was traveling through the porous passages in the coating and getting between the coating and the internal diameter of the pipe.
To allow work to proceed safely without shutting down the pipeline, engineers recommended a customised and somewhat unconventional solution: creating a nitrogen vapor barrier between the plugging heads to reduce or eliminate hydrocarbon leakage.
That would involve reverse-engineering the ProStopp DS system, which normally flows outward, to flow inward instead.
In the ProStopp DS tool, product that is bled out from between the plugging heads goes up through the control bar of the actuator away from the work area to the control box used to activate (or energise) the plugging heads.
The control box is directly connected to each of the plugging heads on the isolation tool and to the area between the two plugging heads. This setup means that technicians can access the area between the plugging heads, which was key to the vapor barrier approach working.
To create the vapor barrier, technicians plumbed a bank of nitrogen bottles into the bleed line through the hydraulic control box and started flowing the nitrogen back through the actuator, down the control bar and into the zone between the plugging heads. This way if there was a leak, it would be inert nitrogen, not hazardous natural gas.
The good news is that once the vapor barrier was in place between the plugging heads, the downstream LEL monitors didn’t detect any gas, and rerouting activities could continue.
Innovation is a priority
With millions of people depending on them every day for supply continuity, Australian gas distribution operators are always looking for new ways to help them run their networks more safely.
So are the regulators whose oversight ensures the protection of the general public, pipeline operating personnel and the environment.
The service providers who move technology along share the same interest, and the evidence is in ongoing innovation to meet the goals of business and society.
And as for the next big thing in pipeline integrity, it’s probably right around the corner.
This article featured in the September edition of The Australian Pipeliner.
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