Compact Spriax DBB System Reduces SCA's Downtime

Spirax Safebloc Double Block and Bleed valves have helped SCA Hygiene in Prudhoe, Northumberland, to eliminate unscheduled boiler shutdowns costing up to GBP20,000 each in lost production. SCA Hygiene runs a 24/7 process, producing branded tissue. It is the company's practice to only carry out maintenance work on a live-steam system behind double block-and-bleed isolation. The company frequently suffered minor problems with blocked level-gauge glasses on its boilers.

However, because only single isolation valves were fitted to the gauge glasses, the boiler had to be shut down and depressurised to enable maintenance engineers to fix the problem safely, halving production output for up to 10 hours. SCA Hygiene decided to replace the existing single isolation valves with four Safebloc valves on each of its boilers, so that any future maintenance work on its gauge levels could be done without having to shut down a boiler.

Previously, a boiler shutdown could cost the company up to GBP20,000 in production downtime, meaning the last four valves paid for themselves three times over within the first six months. Double block and bleed (DBB) is the industry's best practice for double isolation for safe maintenance without having to shut down the entire system.

Double isolation is achieved by closing two isolation valves, with the intermediate bleed valve being left open to provide a sealing integrity check to ensure the downstream pipeline remains safely isolated during maintenance work. The patented design of Spirax Safebloc incorporates two isolation valves and a bleed port in a compact assembly, making it easy to install into the space left by an existing single isolation valve. According to the company, it had never have been able to install a DBB system in the past as other designs take up too much space, often sticking two to three feet out from the boiler.

An added advantage of Spirax Safebloc is that a retrofit can be undertaken quickly, eliminating the time-consuming and expensive pipe cutting, welding and pressure testing needed to engineer a conventional double block and bleed arrangement from separate isolation and bleed valves. This UK-manufactured and easy-to-fit unit is robust enough for industrial environments. It uses proven technology from the Spirax Sarco range of bellows-sealed globe valves that offer zero gland leakage, while ensuring tight shut-off conforming to DIN 3230 BO1 and ISO 5208 Rate A specifications.

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