Hydrocarbon Engineering - March 2017

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March 2017 HYDROCARBON
ENGINEERING 129
on the burst behaviour. This model is calculated using a finite element
analysis (FEA) to evaluate the stresses on the welding seam and the
rupture disc design.
Figure 8 shows a comparison of the standard and the optimised
rupture disc type. Generally, loads onto a welding seam are not sensible.
The most convenient condition is a welding seam without a load. If this
condition is not possible, different load cases are more suitable than
others. For example, a compressive force is more suitable than a tension
force, but both conditions are more sensible than a bending force or a
shear force. The main stresses are applied on the fixation of the rupture
disc. For the standard version, an extension of the maximum stresses
guided directly to the welding seam. That means that the welding seam is
near the stress peak applying pressure. In this load case, the stresses are
directly guided through the welding seam and a shear force is applied
(Figure 9 – left). Depending on the installation conditions (e.g. possible
flange geometries), as well as the material strength and the quality of the
welding seam, high loads might be affected by the burst behaviour as well
as the lifetime of a rupture disc device. In addition to the standard
solution, the optimised solution shows a stress peak in the same area.
Depending on small geometrical changes in manufacturing, the load onto
the welding seam is reduced respectively prohibited. The stress location
is removed from the welding seam onto the geometrical changes. No
stresses (tension, compressive, bending or shear stresses) are applied onto
the welding seam (Figure 9 – right). Through the reduction of stresses, the
life time of the rupture disc is increased.
Conclusion
The rupture disc used for the customer process has to be chosen in respect
of the known standards and manufacturing technologies. HPRDs have to be
tested to present the best possible solution to protect the customers’
process. One possibility to optimise a standard product is presented within
this article. The optimisation reduces the influence of the welding seam,
which is reasonable for a HRPD longlife version. Furthermore, the testing of
the rupture disc is an important point. High pressure rupture discs, often
used at high temperatures, may behave differently than usual standard
rupture discs for lower pressures. The test investment is much higher, but
essential for a reliable and safe process. The high pressure rupture disc is
thoroughly tested to protect LDPE applications with high pressures and
high temperatures against inadmissible overpressure. Figure 10 depicts the
longlife version of a high pressure forward acting rupture disc. The
differences between the longlife version and the standard version are
visible. As a result of minor geometrical changes, the lifetime of the rupture
disc is increased by reducing the influences onto the welding seam.
References
1. ECOBINE, Informationsnetz im Ökologischen Bauen, 'Polyethylene', (2000),
2. SPITZ, P. H., 'Petrochemicals: the rise of an industry', Edition 1, Wiley, New York,
ISBN 0-471-85985-0, (1988).
3. LIGNELL, D., 'Possibilities of autoclave LDPE process', ARCADA, (2015),
4. EN ISO 4126-2,:2003, 'Safety devices for protection against excessive pressure –
Part 2: Bursting disc safety devices'.
5. REMBE® GmbH Safety + Control, , (January 2016).
6. REMBE® GmbH Safety + Control, REMBE®-Fachtagung 2015, Proceedings, Brilon,
(22 – 23 September 2015).
7. ASME Boiler and Pressure Vessel Code – An International Code, ASME Section VIII,
Devision 1.
8. Pressure Equipment Directive 97/23/EG.
9. AD2000-Merkblatt A1, Ausrüstung, Aufstellung und Kennzeichnung von
Druckbehältern, Sicherheitseinrichtungen gegen Drucküberschreibung
-Berstsicherungen, (October 2006).
10. AD2000-Merkblatt B7 & B8.
11. DIN 2505-1:1990-04: Berechnung von Flanschverbindungen.