Safety in the Plant Rupture Disc and


Safety Valve Isolation and Protection of Safety Valves, using Rupture Discs on the Upstream and Downstream Connections


In recent years several industries have recognized the need to isolate or protected the inlet of safety valve 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 were left for years to flow and ignored as part of the way things were done.


The first step was to try and find better safety valves, which for new plants was simple to build in to the design. But, the 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 plants there was a significant increase in safety valve costs to try and meet the lower emission levels required for certification and permits to necessary to allow start up and be able to continue to run the plants.


While there were significant increases in the capabilities of safety valves, it was still not ideal or meeting the requirements visualized for future zero targets. The 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 poor boy to the safety valve industry, a title they do not deserve. The 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 a “problem” they open and let the pressure out, when in fact that is exactly what they are designed to do, it is still unrecognized by many operators that when the disc performs correctly it is not the problem, but the solution.


So how 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


MARCH/APRIL 2018


performance needed to meet more than a stand-alone safety valve provides to meet zero emissions. 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.


For several years now we regularly see 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.


install lower grade materials in the safety valve, while still meeting all the requirements of design, but with significant reduction in the safety valve capex.


The rupture disc and holder will be a minor cost compared to the exotic or higher specification safety valve capex and if you add in the lower maintenance costs the disc and holder costs you nothing, in fact you are on a win-win path with more production uptime, less emissions, greater safety, overall lower maintenance costs and spares inventory.


But we still see safety valve with an upstream rupture disc failing, needing maintenance and stopping production or causing safety issues, what went wrong?


Let us remember that a safety valve also has an outlet and where is that outlet connected to? In many case the outlet is not a separate line to discharge but is manifolded together with other parts of the plant allowing process gases/vapor to enter the outlet of the valve creating safety valve failures.


Rupture disc for isolating safety valves


The 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. This 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.


The solution of the safety valve manufacturers is a higher specification valve, more exotic materials with higher capex costs as well as increased cost of spares to maintain the valves. Take a typical petrochemical plant with several hundred safety valves and the capex mounts up to be a significant increase in the cost of the valve inventory.


Rupture discs fitted upstream of the safety valve in a material that will isolated and withstand the process conditions leaves the plant owner to


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This is something easily eliminated by a downstream rupture disc to prevent any process gases entering the safety valve on the outlet side. The rupture disc will also block any back pressure from entering the safety valve and remove those concerns during valve selection.


With burst sensors installed both upstream and downstream rupture discs can be monitored and connected back to the control room for system reporting across the plant so operators no instantly which valves and discs are in a green or red state.


The rupture disc manufacturer can in conjunction with design/process engineers work together selecting the rupture discs to give the best possible safety and isolation performance. Unfortunately this is still a rarity and is a factor in the rupture disc getting the blame for poor performance when all it is in fact doing is what it was designed to do, be the most important safety device in the plant, your only fail-safe device that always opens when faced with an over pressure situation.


Case history: Refinery application where safety valves failed in operation due to process conditions attacking the metal structure.


REMBE was approached by the refinery to assist them overcome serious issue with their safety valves. The plant requirement was to be able to operate for 3 years without safety valve removal for service and recertification except in emergency cases. On removal of the safety valves at a scheduled shutdown several valves were found with broken or cracked springs, springs corroded to failure point, bellows corroded and


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