Advances in pressure relief valves and associated monitoring systems help process manufacturers reduce emissions, increase performance, and make other improvements.
Process manufacturers are faced with many challenges, and in this column, we will discuss how to best cope with these issues in the areas of safety, sustainability, reliability, and productivity. More specifically, we will examine how pressure relief valves (PRVs), a seemingly simple—but in fact, sophisticated—device, can help improve performance in all these areas.
Safety: A Non-Negotiable Priority
Over the last few decades, the emphasis on safety has increased significantly due to regulations, insurance, public perception, and recruiting. Consequently, protecting personnel, equipment, and the environment has never been more important.
Regulatory pressures may ebb and flow, but they are increasing over time and will continue to do so. Similarly, insurance rates and public scrutiny only seem to grow. Meanwhile, personnel are increasingly difficult to recruit and keep, and a safe workspace is critical to ensuring retention. Finally, equipment and construction costs have risen markedly over the past few years, so avoiding safety incidents that cause material damage is also more important than ever.
PRVs prevent safety incidents from occurring in all types of pressure vessels, boilers, reactors, and other process equipment. In the past, these devices simply opened at setpoint to release pressure to the atmosphere, and once pressure dropped, they returned to a closed position, ready to activate when another overpressure event occurred. There was no direct indication of opening or closing, so operators had to determine activation indirectly.
Manual inspection rounds are an option, but these activities often require plant personnel to enter hazardous areas, and to access valves in hard-to-reach locations. Adding an external monitoring device that will not interfere with the PRV’s ability to open is a better approach, and acoustic monitoring devices supporting wired and wireless protocols (Figure 1) are now available and designed for mounting directly on pipes adjacent to PRVs.
An acoustic transmitter (blue device in the upper left of the photo), can be mounted on the discharge pipe of a PRV, allowing it to detect the vibrations caused by any release. These devices send data via WirelessHART.
These devices can detect PRV events in real-time, and analytics can correlate process data with maintenance records to determine root causes. Immediate notification via wireless communication with a host system keeps workers safe and ensures regulatory compliance.
Sustainability: Going Beyond Compliance
As with safety, sustainability has increased significantly in importance, moving from an afterthought to a necessity as public demand for more environmentally conscious practices has increased.
Releases and leakages from PRVs open to atmosphere can lead to fines, lawsuits, and extra work related to identifying the source of each release. Even small leaks can generate large amounts of volatile organic compounds (VOCs), depending on concentration and pressures.
As with safety, PRVs can now play a vital role in improving sustainability, but only if their operation is continuously monitored to detect release events. The same type of monitoring can detect release events, and it can report their duration and severity, and quantify the amount of emissions. This information empowers plant personnel to quickly identify issues, and to then repair or replace the defective device.
Reliability: The Foundation of Operational Excellence
Reliability is particularly important in industries facing intense global competition. Downtime can be costly, not just in terms of lost production, but also in unplanned maintenance costs. This increases the drive for maximum uptime with minimal operating expenditures, along with the need to detect minor issues before they develop into serious incidents.
A PRV release is not a regular event, and as such, each occurrence should be logged for further investigation. If a PRV opens frequently, that is a strong indication of a process problem that deserves more attention, or of a valve not properly specified for the application. In either case, it should be treated as an important alert by operators.
Once again, PRVs play a crucial role as they can warn of impending issues with their own operation, as well as with the equipment they are designed to protect. Unmonitored PRVs simply operate as designed until they fail, with detection of even complete failure often difficult.
By contrast, monitoring also reveals if a valve is leaking or simmering, and alerts for unwanted behaviors, such as cycling or chattering. With real-time information about each release, correlating relief events with process data becomes possible, helping to detect issues with the equipment to which the PRV is affixed.
Relief events can be correlated with historical records and maintenance data. Process manufacturers can perform a much more in-depth and accurate root cause failure analysis not only on the valves, but on the process as well.
Productivity: Automation Meets Efficiency
There are two aspects of process plant productivity: personnel and production. The drive to increase personnel productivity has amplified as the difficulty in hiring and retaining staff has grown, but process manufacturers can work with suppliers to increase automation, multiplying the efforts of their staff. The demand to increase production process productivity is also growing due to the aforementioned heightened worldwide competition.
Both these issues can be addressed with PRV monitoring. As previously stated, manual rounds to inspect PRVs are problematic from a safety standpoint, but they also negatively impact productivity. By removing the need for manual rounds to inspect valves, these systems free up personnel to focus on higher-value tasks, such as supervising numerous sites from a control center. Software applications are available to speed and simplify these monitoring activities.
Automated PRV monitoring also increases production productivity by providing early warnings of impending issues in the devices themselves, as well as in external equipment. This helps facilitate proactive and planned maintenance, rather than reactive upkeep, eliminating the extra costs and downtime that accompany the latter.
Ongoing advances
In addition to monitoring, instantaneous bellows leak detection is a critical safety feature designed to immediately identify and alert operators to leaks occurring in the bellows of PRVs. Bellows are integral to isolating the valve’s internal components from external factors such as process backpressure, which can influence the PRV’s setpoint and performance. Over time, bellows can deteriorate due to mechanical stress, corrosion, metal fatigue, or exposure to harsh process environments. This deterioration can lead to small or significant leaks, compromising the effectiveness of the valve and introducing several safety hazards.
Service records from 30,000 valves in multiple applications and industries show that 2-6% of all PRV bellows are damaged and potentially emitting flare gases to the atmosphere. Incorporating instantaneous bellows leak detection into PRVs is a proactive safety measure that mitigates risks associated with bellows failure to ensure operational reliability, environmental protection, and compliance with safety standards.
These types of advances will persist as automation suppliers continue to innovate; a commitment Emerson takes very seriously. Combined with monitoring systems, modern PRVs are helping process manufacturers increase safety, sustainability, reliability, and productivity, now and into the future. And though we’ve come a long way as an industry, we’re certainly more focused on where we’re going.
About the author
Peter Mathew is the vice president for Emerson’s Pressure Relief Valves business unit, and he has over 15 years of relevant industry experience in general management, operations, sales, and marketing. Mathew holds a bachelor’s degree in business administration from Oklahoma State University, and he completed the Global Leadership Program through Duke University.
