Making DBB look easy

Simple and easy aren’t two words usually associated with double block and bleed (DBB) isolation. Though they provide front-line defence against risk during pipeline maintenance, repair, and replacement, traditional DBB tool installations with two separate single seal heads can be a beast.

Depending on pipeline conditions, these heavy, complex tools can also be tricky to deploy or can get stuck in the line, adding steps and stress to the process, and blowing through your budget. All those fittings and bolts mean more hands on deck, more headaches, and more hardware left on the line. And a single failure can trigger a cascade of threats, especially in high consequence areas (HCA).

WeldFit, a provider of pipeline products and services, has attempted to streamline the pipeline intervention process with the Dually® Double Block and Bleed Line Stop System. Since it was introduced in 2023, the Dually system has been installed at more than 60 job sites, performing more than 110 line stops – testimony to the device’s real-world capabilities.

Available for 8 in. through 42 in. pipelines with a maximum operating pressure of 1480 psi (102 bar, 600 class), the Dually system provides a redundant barrier against product leakage with far less setup time. That helps pipeline operators bring assets back online more quickly, reducing revenue loss associated with downtime.

A straightforward take on DBB technology

DBB systems typically involve two plugging heads to completely isolate a section of pipe and a bleed valve that ensures the safe venting of residual fluids or gas.

A patented innovation designed for both gas and liquid pipeline intervention, Dually builds on WeldFit’s success with single seal line stops, achieving DBB functionality with a compact, straightforward tool.

Dually utilises a single pivoting-style plugging head with dual seals that isolate pressure, providing an added layer of verifiable safety. The single pivot point design makes it easier to insert, deploy, manoeuvre, and remove. Plus, there are fewer individual pieces to handle, transport, and assemble in the field, and half the taps, fittings, bolts, and welding points as conventional DBB.

The industry has trusted a single stop design for years but wanted double block and bleed for even more crew safety. Other companies have developed double block and bleed solutions that have had operational challenges in the field, which WeldFit believed it could fix, and decided to work with the concept that’s trusted versus developing something entirely new.

It took the traditional plugging head, which has been used in the industry with a standard fitting and a standard single pivot point for some 70 years and found a way through technology to collapse the seals down in such a way where you can fit it all through the same size hole, which is more reliable, simpler to use, and typically provides the quality of seal that customers require.

For any mechanical seal to function optimally, it needs to make uniform contact with a clean surface. Chips or debris left as the result of the tapping process can create gaps in the seal, letting product leak past. Dually’s chip-sweeping capabilities better remove any foreign material that could interfere with a tight seal.

Improving control

WeldFit created a pressure-free Zero Zone between the seals that acts as a reliable indicator of an effective isolation – any leakage past the first seal would cause a detectable pressure spike in the Zero Zone, instantly flagging a problem.

Beyond detection, the Zero Zone allows for the safe release of any lingering product or vapours trapped between the seals once isolation is confirmed via an onboard gauge. Operators can purge the Zero Zone through an internal bleed port to create a fully depressurised space, enabling technicians to work in a zero-energy environment and ensuring maintenance or repairs can proceed with maximum safety.

Gas has to be allowed to move around, but also controlled in where it moves. Even if gas enters the Zero Zone, it is contained within the Zero Zone and its path forward is isolated, preventing it from passing the secondary seal, or leaking out through any connection points on the very front of the tool that might be exposed to the atmosphere, which ensures the integrity of the work area.

The Zero Zone functions as a robust safety mechanism that:

• Verifies the integrity of the upstream seal.
• Provides a controlled means to depressurise the isolated area.
• Allows for the safe removal of hazardous product or vapours.

A matter of gravity

The Dually system is compatible with diverse pipeline products, including natural gas and NGL, and has been effectively implemented above and below ground, in tight trench boxes, and excavations, meaning it’s a practical choice in all common pipeline maintenance scenarios, even in confined spaces.

Dually has also been successful when deployed in difficult geometries where standard solutions might fail, such as precarious angles.

When pipelines aren’t horizontal, gravity can work against the process of inserting and setting a heavy DBB tool. If the weight of the tool isn’t distributed evenly, the tool might shift or slip, potentially damaging its sealing mechanisms, not to mention the pipeline itself. An angled pipe might be difficult to seal – the sealing elements might not conform to the walls of the pipe. Working on a pipeline at a precarious angle often means limited and awkward access for technicians and equipment. This can make the installation, operation, and monitoring of the DBB system more difficult and time-consuming.

But because of Dually’s compact design it is less susceptible to gravitational forces, meaning it’s equally easy to insert and remove, regardless of the pipe’s angle. Under conditions where other DBB providers were reluctant to go, Dually performed flawlessly, showcasing its versatility.

Real world trials

WeldFit began development of Dually in April 2021, moving into rigorous proof testing that simulated defects under controlled conditions and extensive field trials to validate the system’s reliability under real-world pipeline conditions before its release. Proof testing of the head and components was performed at 1.5 times design pressure (2220 psi for 1480 psi rating, or 151 bar for 102 bar rating); additional testing included deploying the tool in the thinnest and thickest wall pipes to ensure compatibility with every schedule of pipe, and function tests without pressure to check deployment and retraction.

Independent testing is performed at pressures much greater than what will ever occur on a pipeline. A significant field-testing phase involved working with a major North American operator at 12 US sites along 50 miles of 20 in. and 24 in. diameter pipelines. Testing was conducted over six months, from May to November, under varying weather conditions and pressures. Each deployment lasted approximately 30 days, and the system remained online throughout the test period.

“We had never predicted that some of these heads were going to be in the line for 30 plus days at a time,” Chris Peavy, WeldFit line intervention services coordinator, said. “That longevity alone is incredible. And because we didn’t need to rework, unbolt bypasses, or reattempt seals at any of the 12 job sites, it saved significant time and cost.

“Even if you say we saved two days per site, that’s 24 days of savings on cranes, construction crews, excavators, and labour. That equates to millions of dollars of savings for our client,” he added.

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