Chemical & Process Technology

This is a continuous post from "Useful Documents Related to Pressure Relief Valve (PRV) - Part 1"...The following are comprehensive series of articles related to Pressure Relief Valves by Valve World. For thus of of you are dealing with Pressure Relief Valve design, specification, Operation, monitoring and maintenance should not missed this series of articles.

Pressure Relief Valve Types, Codes & Testing
by Lester Millard
Generally speaking, safety relief valves have been around since the 1600s in more or less the same design concept. In its primary function, the pressure safety relief valve serves to protect life and property. Acting as a 'last resort', this fully mechanical valve is designed to open based on an over pressure situation within a process pressure system, thus not only protecting life but safeguarding the investment and plant itself. This article reviews the principles of pressure safety relief valves for spring loaded and pilot operated designs. It will cover the applicable European and American codes and standards as well as end user procedures that are key elements in establishing safety and safe selection. Testing (set pressure verification) and maintenance - important criteria once the safety valve has been installed and commissioned - will also be addressed. Pressure safety relief valves should be taken very seriously. Manufactured from castings they may not look very sophisticated, but in their design, accuracy and function they resemble a delicate instrument whilst performing an essential role. Self-contained and self-operating devices, they respond to system conditions and prevent catastrophic failure when other instruments and control systems fail to adequately control process limits...

Back-Pressure effects on safety valves operating with compressible flow
by Vincenzo Dossena
The effects of back-pressures on safety valves is a potentially serious problem, but one only now being recognised by the valve industry. Research has been performed by the University of Milan, as reported in the June 2002 issue of Valve World. This report is also printed in full below. In addition, please note that RWTH's Hans-Dieter Werker has presented a paper entitled "Influence of back pressure on function and flow rate of a direct loaded safety valve" at the Valve World 2002 Conference in Maastricht.

An investigation of safety relief valve set point testing techniques
by E. Smith
In 1995/6 a BP group-wide work group met to consider various aspects of safety relief valve management and performance. One subject considered was the setting of these valves and, in particular, the use of on line set point verification (OLSPV). Traditional methods of testing such valves in BP Amoco group companies conform to the recognised industry standard API 576, and the usual procedure requires that all PSVs are removed from the plant periodically so that their condition can be evaluated in a workshop. Prior tore-installation valves are then "pop" tested on a test bench. On steam boilers the bench set pressure must also be proven in-situ by "floating" the valve. This method is both time consuming and costly. There are, however, methods of testing safety relief valves on line (with and without pressure), notably the Furmanite 'Trevitest" safety valve testing system and comparable in-situ test systems offered by e.g. Crosby and Consolidated. The benefits of these methods are lower costs and, where valves are not "spared", extended plant run times.

Safety valve noise; limits, reduction and control (PDF)
by M. D. G. Randall
What is a safety valve? How often, long and loud is its noise?
The safety valve is a device to avoid a dangerous build-up of pressure within a system that it is designed to protect. One should never forget that any redesign of the PSV system must not decrease the safety of the protected system. A safety valve is normally used with compressible fluids, whereas a relief valve is primarily used with incompressible fluids (see the introduction to Ref 1). The safety valve is generally known as a PSV and may release the process fluid directly to the atmosphere via a short stub pipe, or release the process fluid via a pipe to a flare, or some other equipment. These will be called "open vent" and "closed" PSV systems, respectively. A PSV is actuated by upstream pressure and is characterised by what is described as a "pop" action upon opening. It is important to recognise that one should not expect a gentle release of gas proportional to valve lift.

Standard Related to Pressure Relief Valve
Simple compilation of Standard Related to Pressure Relief Valve