SAFETY IN THE PLANT
THE IDEAL
Claire Lloyd discusses using rupture discs for isolation and protection of safety valves
plants there was a significant increase in safety valve costs to try and meet the lower emission levels required for certification and necessary permits to allow start up and be able to continue to run the plants. While there were increases in the capabilities of safety valves, it was still not ideal or meeting the requirements visualised for future
zero targets. Te expectation was that safety valves could not meet the
requirements and an alternative solution was needed: enter the rupture disc. Rupture discs have been around for decades and were always seen as the secondary solution for overpressure after safety valves, the second-class citizen of
Ideal combination – safety valve and rupture disc
I
n recent years several industries have recognised the need to isolate or protect the inlet of safety valves with rupture discs, but many have missed
the opportunity to fully protect the safety valve from the effect of process conditions entering the outlet side of the valve. Many years ago, the various industries, in many cases driven by legislators and environmental groups, faced the need to improve the rogue emissions that had for many years been almost ignored as part of the way things were. Te first step was to try and find better safety valves, which for new plants was simple to build into the design. But existing plants were looking at substantial investments to replace older designs with newer ones, not an economical choice in a large majority of cases. Even for new
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the safety valve industry, a title they do not deserve! Te lack of understanding of the rupture disc continues to this day. It is still a mystery to engineers in the mechanical and process disciplines and to the field operatives that install and maintain them, or in a lot of cases ignore them. Discs are perceived as being
a “problem”. Tey open and let the pressure out, when in fact that is exactly what they are designed to do. It is still unrecognised by many operators that when the disc performs correctly, it is not the problem, but the solution. So how
COMBINATION For several years now we have regularly
seen rupture discs being installed upstream of a safety valve. Operators are now starting to appreciate that a properly engineered rupture disc will help lower their operating costs and increase the up-time for a plant. Te belief that this arrangement adds
more cost into a project has been proven to be false: in fact the opposite is the case, costs come down. Take a typical installation where the
safety valve faces a process condition with high concentration of corrosive materials, increased temperatures and an operating pressure close to the safety valve set pressure. Tis tests the limits of safety valves and we see poor performance below the expected levels needed for operational stability and no leaks. High maintenance costs are needed to keep the valve as close to original specs as possible, increased downtime to the production for routine valve servicing and/or repairs and higher manpower costs to cover the work scopes.
WHAT’S THE ANSWER? Te solution of the safety valve manufacturers is a higher specification
valve, more exotic materials with higher
does the rupture disc help the safety valve perform better in use? Well in the case of isolation it partners the safety valve and brings the superior performance needed to meet zero emissions more than a stand- alone safety valve provides. Yes the safety valve can have good performance levels on its own, but achieving 100% isolation and providing better operational stability requires the use of rupture discs.
Rupture disc for isolating safety valves
CAPEX costs as well as
increased cost of spares to maintain the valves.
Te use of a rupture disc in front
of the safety valve allows for the use of valves in standard materials, isolated from the process by a ‘more exotic’ rupture disc.
Claire Lloyd is with Rembe.
www.rembe.de
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