N E W S   R E L E A S E   from  FURMANITE  AUSTRALIA  

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On-line valve testing reveals inadequate protection

Safety and relief valves installed on plants across a range of industries may not be providing adequate equipment protection or could be impacting on plant performance because they are set incorrectly, technical services company Furmanite is warning operators.

The concern comes following a survey of safety valves on plants from power to refining and minerals processing, comparing test pressures against the manufacturers’ set pressures, which reveals some alarming discrepancies.

“We’ve tested a wide range of safety valves in various sizes on plant equipment from boilers, superheaters and steam drums, to off-gas units and acid plants, on-line, without disrupting operation, using Trevitest technology which is highly accurate to within plus or minus 1% of the set pressure,” Furmanite regional sales manager David Arnold explains.

“What we found was that less than a tenth of the valves tested were within 1% of the manufacturer’s set pressure with, worryingly, over 90% showing deviations of anything up to 21% from the set pressure.”

Most commonly valves were found to be set above the manufacturer’s set pressure (82%), indicating that both the line from valve to equipment and the equipment itself could be inadequately protected by these devices. Notably, some 26% showed a difference between test and set pressures of 10% or more. On the other hand, 18% of the valves were found to be below set pressure, so potentially unnecessarily impeding plant performance and reducing efficiency.

“Interestingly, these findings demonstrate that relying on bench testing is considerably less accurate than testing on-line using Trevitest,” Arnold points out. “This could be down to human error in interpretation of the bench test, possible damage in transportation from the workshop back to the plant which is affecting the set pressure, or could be due to distortion of the valve body when reinstalled into the plant. All are potential errors which can go unnoticed if the valves are not checked on-line once reinstalled.”

Trevitest on-line valve testing technology for safety and relief valves works by applying a force to the valve spindle to overcome the spring tension of the valve. This is achieved using a hydraulic power pack attached to a specially designed set of mechanics (an adjustable frame with hydraulic rams and a load cell) mounted on the valve, and an electronic force transducer, which is linked to a portable computer, to trace the force applied. The recorded data, together with knowledge of the valve seat area and line pressure of the valve, enables the set pressure to be computed.

A date-marked certified print-out of the valve performance is produced, showing valve set pressure and line pressure at the valve. In addition to the set pressure, the spring adjustment and displacement of the valve can be determined from the information recorded, and an indication gained of the effect of the nozzle ring, guide ring and reseating pressure. Sluggish valves, passing valves, valves with long blow down or with long simmers can all be identified from the recorded trace. Moreover, the results and print-outs provide an auditable history trail and comprehensive valve test diagnostic record.

“Issues of incorrectly set valves can be easily overcome by testing on-line using Trevitest,” Arnold advises. “If necessary they can then be adjusted on-line and re-tested easily. No valve is signed off until it’s seen two consecutive correct recorded test pressures.”

A further advantage of Trevitest is the ability to test valves at normal operating pressures and temperatures in advance of scheduled shutdowns, so that only those needing overhaul need be removed from the line during the outage, helping to reduce time pressures, costs and avoid delays in the outage schedule.

“This is another service in our portfolio geared to helping operators keep their assets performing efficiently and maximising uptime,” Arnold comments.

For further press information contact:
Sarah Manwaring-White
Keep in Touch Ltd
Tel: +44 (0)1451 844 488
Email: sarah_mw@keepintouch.co.uk