Production • Processing • Handling
Reliable pressure relief on flare systems
Sandra Fuchs dispels the myths surrounding rupture discs. O
ver the past decade the use of flares to burn off hydrocarbons has been significantly reduced and in some countries all but eliminated, except for unusual or emergency cases. To
achieve a safe system to recover the hydrocarbons, end users have modified their processes and used recovery systems to channel the once waste gas back into the plant or use it directly for secondary purposes such as injection or utility fuel. To ensure that the flare is still available under
certain conditions that require the reliable opening of the flare line, various valves and controllers are employed. Te problem can be that these are not failsafe and may not respond and open fast enough, or at all, in an emergency. How can a reliable and safe installation be ensured? Enter the Rembe bursting disc, a reliable and failsafe opening device. Tere are a lot of myths surrounding bursting discs (also known as rupture discs), since most design engineers have no training or experience in this field. It is a subject that is not covered in any university undergraduate engineering degree. Many different types of valves and piping control systems are covered, but not an item that is often the most important safety device in the plant! Te usual way of specifying rupture discs is to apply the same data and knowledge used for safety valves. Tis isn’t really an appropriate method. A bursting disc needs the right design criteria if it is going to operate to suit the process conditions that
it will help control. Myth number 1 is that ‘discs always fail’. Here
we need to define the word fail. Does this mean premature bursting, leaking discs or that the disc is bursting often and needs to be replaced? Premature burst is sometimes prevalent with older designs of rupture discs. Tese discs are mechanically scored to set the burst pressure. Incorrect fitting techniques, mechanically induced stresses and the operating pressure exceeding the operating ratio can all damage the disc and cause the disc to open at a lower set pressure than that specified.
Leakage of mechanically scored rupture discs can occur due to pin-holing or cracking of the score line. Tese mechanically scored discs are susceptible to damage due to mechanically induced stresses, corrosion, vibration and incorrect fitting techniques, which can all contribute to leakage along the score-line. Rembe bursting discs are not mechanically
scored. Te KUB, for example, is a two-layer disc where the burst pressure is controlled by a laser-cut element on the downstream side of the process. No scores or other marks are facing the system process, thereby increasing the durability and increasing the service life of the disc. Frequent bursting is a common complaint.
History shows that upon investigation, repeated opening of the discs is usually due to the operating envelope being exceeded. In many cases the operator
Fig. 1. Users are finding the Rembe bursting disc a reliable and failsafe opening device.
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