By Michael Werner, Power Industry Sales Manager, GE Energy’s Consolidated product line
In steam boiler applications, pressure relief valves (PRVs) are the silent sentinels – the last line of defense against potentially disastrous overpressure situations. In a perfect world, boiler pressures would never approach unsafe levels and the valves would never be called into action. However, if and when the valves are needed, they must perform.
Spring-loaded pressure relief valves are designed to deliver long-term reliable overpressure protection. Step one in achieving that goal is specifying the correct valves for the specific application, based on accurate information about boiler conditions and adhering to the rules provided in ASME Section I, paragraphs PG-67 through PG-73. That is the easy part, and just the beginning.
Also required are the proper design of the entire pressure relief system, correct installation of the valves and other system components, and ongoing maintenance of the system. Setting up a boiler’s pressure relief valves for a full life of service requires the combined efforts of the boiler design engineer, the construction team and the end user’s maintenance team.
This article reviews the “to do” list for each member of that team, providing checklists for each to reference. These are, by necessity, general guidelines, as every application is unique; readers should also consult the pressure relief valve manufacturer’s installation and maintenance manual for additional information that is specific to their situations.
Checklist for Boiler Designers
Many of the pressure relief valve-related issues that occur in boiler applications are not related to the valve, but are the result of inlet, outlet or accessory issues. These issues can cause excess vibration (mechanical/sonic), inlet pressure loss, outlet pressure buildup and binding of materials, all of which can negatively impact pressure relief valve performance.
Boiler designers can prevent these issues by completing a thorough review of the pressure relief valve “system” prior to final release to the construction team. The following checklist identifies key items to review.
Checklist for the Construction Team
The construction team takes over when safety valves are received at the job site.
Prior to delivery, the valve manufacturer will assemble and test the steam safety valves to meet ASME Section I, paragraph PG-73. The appropriate ASME Certification Mark and Designator stamps (ASME Sec. I-“V”) are then applied to the valves after successful factory testing.
The boiler manufacturer and valve manufacturer will provide boiler OEM (Original Equipment Manufacturer) drawings, as well as installation and maintenance manuals, to guide the construction team in storing and installing the PRVs, but it is imperative that the valves are installed by an installation team with previous experience successfully installing PRVs. The following steps should be completed by site construction, warehouse and installation teams to ensure that the manufacturers’ recommendations are followed.
After the final review and sign-off, the PRVs are ready for use during boiler operation.
Checklist for the Boiler Maintenance Team
It is important to remember that a PRV is designed to remain closed more than 99 percent of the time, only opening when needed to protect people, processes and/or the boiler during an overpressure situation. The fact that a PRV is “not leaking” does not indicate that it will work properly if needed. For example, if valves are closed for long periods of time, scale deposits can build up, causing the valve to stick in the closed position.
Periodic inspection by an authorized service provider (VR stamp holder) will help ensure that the valve will perform its duty when called upon.
Boiler PRVs can deliver long periods of reliable overpressure protection. All it takes is teamwork by the boiler engineer, construction team and end user to ensure that the system is properly designed, installed and cared for. That effort can deliver significant results, such as increasing safety, decreasing performance problems and lowering the lifetime cost of ownership.
Power Engineerng Issue Archives
View Power Generation Articles on PennEnergy.com