Paul Shillito, our engineering director at Oliver Valves, looks at cartridge-style double block and bleed valves and their benefits in pipeline isolation applications.

Right along the oil and gas supply chain - from extraction through to delivery to the end-user - safety is the number one priority. The ability to shut off the flow in a pipeline with a 100 per cent tight seal is essential, whether in reaction to an emergency scenario or so that inline repairs or maintenance can be carried out.

Some isolate valves are installed purely as a safety measure and may never need to be closed. Others may sit inactive on a pipeline for many years before being required, and yet still must guarantee 100 per cent performance in the event that they are needed.

For pipelines that transport crude oil, natural gas and their derivatives, double-block-and-bleed (DBB) isolation valves are mandatory. This measure, brought in by the Cullen report in 1990 in response to the Piper Alpha disaster, means two separate valves are required with a means of releasing the pressure and draining the space in between.

The idea is that if the first valve lets any material through, it will leave via the open bleed valve rather than through the second isolate valve and into the downstream section of the pipeline where it could cause an incident. However, this presents a challenge, particularly in modern offshore projects involving floating production and storage facilities which put a premium on weight and space.

Conventionally, in order to achieve a double block and bleed system, two standard isolation ball valves would be installed, along with a separate facility for bleeding the pipework in between.

However, where space is of the essence, this approach more than doubles the space required compared with a single valve system. This can make the installation unfeasible, especially where multiple valves along the line need to be upgraded.

Cartridge-style DBB valves

To tackle the challenges inherent in the traditional system - which requires three times more connections than are needed for a single unit - we've pioneered the single-unit cartridge-style DBB valve. Our valve solution incorporates three valves into a single housing. The result is a valve that increases the safety of the system by removing connections between separate units, resulting in fewer potential leak paths.

The volume of the cavity between the valves is also reduced, allowing operators to evacuate the space and establish a safe isolation more quickly - a potential benefit in emergency scenarios. In addition, our design has the same face-to-face length as a standard single isolate valve, as specified in API 6D and ANSI B16.10.

Not only does this mean that it can be easily installed into an existing structure without re-working the surrounding pipes, but it reduces the space required for a double block and bleed system by more than half, freeing up room for other equipment.

Additionally, because the valves are full bore, they offer a negligible pressure difference when open, maximising efficiency and allowing maintenance and inspection pigs to pass through them.

Going forward

Oil and gas pipelines will continue to be a critical part of our infrastructure for many years to come, as millions of people around the world depend on the essential fuels and other derivatives they transport. It is with this reality in mind that regulations are being tightened around levels of emissions from pipelines and around the safety measures that are in place to control the flow of materials within them. Valves play a fundamental role in meeting these standards, and the industry's leading manufacturers are constantly pushing the boundaries of performance to help their clients in the energy businesses meet these goals.