Safety in the Plant

of the different input values can have a significant influence on the outcome. The general principle is as follows: The functioning of a

spring operated safety relief valve is based on a pre-stressed spring. When the spring force is reached the valve disk starts to move and the valve opens. With lifting equipment attached to the valve spindle, the

valve is opened and the lifting force measured taken into account exact seat area and operating pressure. Set pressure is calculated with equation:

It is of highest importance that all factors used to calculate the set pressure is as accurate as possible, especially the pressure under the safety valve (Po

) and its stability over the time of measurement.

Bursting disc

It is critical that all conditions at the valve inlet need to be stable. This can only be achieved if an suitable bursting disc is used to isolate a safety relief valve inlet from the process and for the duration of the in-situ testing a stable and monitored pressure is applied (minimum 70 per cent of set pressure would be recommendable). Special designed bursting discs with a bypass needle

Where:

Po

Fs As

= Operating pressure = Force on spindle = Effective seat area

The applied auxiliary force applied to the spindle is usually software-controlled; a force sensor registers the additional force necessary to lift the valve spindle. Chronically with the lift force measurement, the pressure at the inlet of the valve must be measured. The set point result is achieved by calculation where the

achieved accuracy will depend on the accuracy and stability of the measurements at the time of the test over a period of time. The best accuracy proven and advertised by most in-situ

test providers is 3 per cent; this is the limit of deviation of set pressure allowed by ASME VIII & PED when setting a relief valve.

valve between process and a pressure sources could offer a solution. In-situ testing is a good alternative test method for safety

valve set pressure validation if necessary precautions are taken. It is recommended that experienced personnel carry out these tests and that the factor of uncertain and unstable upstream pressure is eliminated by using a rupture disc arrangement upstream of the valve which:

❒ Protects the valve from possible plugging and corrosion, providing a clean break away force during in-situ testing.

❒ Allows pressurisation upstream side of the valve up to 70–75 per cent of set pressure assisting the lifting devices.

❒ Allowing faster in-situ testing and correct calculation of the set pressure.

Fire and explosion solutions

Fike is a globally recognised supplier of products and services that protect people and critical assets from dangers such as fire, explosion and over-pressurisation. With more than 60 years experience manufacturing

products ranging from rupture discs and explosion protection systems, to fire suppression and fire alarm systems, Fike offers reliable solutions for customers around the world. These are intended to deliver reliable safety products that exceed customer expectations. Overpressure conditions can lead to a variety of disasters

– injuries, damaged equipment, business interruptions and downtime. To help solve these problems, the company offers an

inexpensive solution – quality rupture discs and rupture disc accessories Specialists in rupture discs (rupture disks), bursting discs and

the isolation of pressure relief valves, Fike has specific rupture disc products for different applications, rupture disc isolation procedures for pressure relief valves (safety relief valves), rupture disc calculation tools and rupture disc accessories and holders. The company’s laboratory and testing services are available

to certify custom products developed for specific customer applicdations, including those manufactured for aerospace/ defence contracts, special gas handling applications and many other variants of standard product offerings. ❒

Enter 39 or ✔ at www.engineerlive.com/ece Above: Installed safety valve with bursting disc.

Roger Bours is Manager Pressure Relief, Herentals, Belgium. www.fike.com or www.fike.be

www.engineerlive.com 39 Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44