Relief valves are important safety devices protecting the plant and personnel by relieving over-pressure events to the atmosphere or a flare. After a release, it is not uncommon for the relief valve to not seat back properly. This causes the valve to pass internally, allowing valuable product, feedstock, or other material to escape unnecessarily during normal operation.
Although each leak in many cases may be small, with hundreds of relief valves across the plant, over time this translates into significant material losses. Plants literally can witness their profits going up in smoke or disappear into thin air. Because hundreds of relief valves may share a common flare, it is not easy to pinpoint which relief valves are leaking and which ones are not. In this article, Jonas Berge explains how smart plants are cutting their product losses by dropping in wireless acoustic transmitters and often see immediate results.
Relief valve leaks
Out of the relief valves that fail to reseat properly, many leak small amounts, but a few may leak profusely.
Plants can measure an increase in flared amount over time, and mass balance calculations also reveal losses.
Plant management keeps track of losses, and plant personnel are on the spot to minimize these losses.
Reducing losses, minimizing flaring, and reducing the carbon footprint are industry-wide trends.
Best practice in the past was to routinely pull relief valves into the workshop for inspection and overhaul, without much information about the expected condition of the relief valve. However, dismantling and overhauling relief valves this way is very labor intensive and can consume considerable time if parts are hard to obtain.
An acoustic transmitter turns an ordinary relief valve into a smart relief valve.
Relief valves are often in difficult to access locations such as on top of vessels or pipe-racks that require scaffolding and a crane for inspections and removal.
Conducting manual leak testing with a portable acoustic tester to survey the relief valves in-situ is a somewhat better approach. However, periodically checking hundreds of relief valves is still very labor intensive and therefore does not get done frequently enough. Each condition check is a snapshot in time and a lot can happen until the next survey. The process includes establishing a test route, scraping loose paint and brushing off rust for each valve, checking that the line is pressurized, applying contact compound on the probe and holding it in place, taking a reading and recording it on a check sheet. Inspection rounds must be frequent to be effective.
Continuous relief valve condition monitoring
Continuous monitoring of relief valve condition is more effective for identifying leaking valves than periodic testing. An acoustic transmitter is easily installed on each relief valve to be monitored. The acoustic transmitter can detect and report both relieving events and leaking relief valves typically every minute or as quickly as once per second if needed. There is no need to send personnel into the field to perform these diagnostics and there is no need to remove the relief valve or take it out of service.
The relief valve remains in-situ, no shutdown or bypass is required, and it has no impact on the process. The acoustic transmitter with digital communications turns an ordinary relief valve into a smart relief valve by providing diagnostics.
Because acoustic transmitters are non-intrusive, they are very easy to install and a low risk to deploy. The sensors clamps on to the outside of the valve using metal clamping bands or a bracket. There is no cutting, drilling, or welding required. No process penetrations are created.
Furthermore, a wireless transmitter requires no power cables and no signal wires so there is no risk to the existing installation associated with opening cable trays or junction boxes. The wireless transmitter is powered by a battery that lasts up to 10 years with a half minute update period.
Continuous relief valve monitoring gives plants the ability to detect leaking relief valves immediately and service them early to stop losses much sooner than was possible in the past. Indeed, at most plants where acoustic relief valve condition monitoring has been deployed, one or more relief valves that may have been leaking for a long time were detected; instant gratification.
With automatic monitoring, maintenance personnel spend less time pulling relief valves or manually testing for leaks, and can instead focus on repairs of those relief valves that are found passing.