Benoil Services Ltd

Testing Development - Extreme nominal-burst-pressure testing at elevated down-hole temperatures
test cell
The test cell is designed to replicate the conditions of the tool in which the burst discs will be used. This is both in terms of the geometry within the 'ports' for example, as well as the temp/pressure environment. Each test piece is held and assembled into the test rig using the same threads as secures the discs in the tools. In this example a metal-metal seal is used. However O-ring seals have been tested to high pressures as well. The disc once loaded is tightened to torque. The temperature aspect of this test is achieved by immersing the test cell into a hot oil bath. High pressure hydraulic feed and drain connections are provided both sides of the disc - should a reverse direction test be required. With the end cap being a simple screw fitted assembly of O-ring, lock ring and cap, rapid change-overs of the test sample can be achieved. The highest rated and tested products we have to-date are 215°C // 400°C and 25,000psi. Burst pressures are accurate to ±2.5psi and temperatures to ±1°C.
Test cell port geometry The screw-fit end cap contains the viton (DuPont) O-ring and the lock ring required for higher pressure sealing. The fine gauge thread used on the cap ensures a progressive torque build to the sealing O-ring.
Also within the test cell itself can be seen the metal-metal seal used in this burst disc application. A 'square' shoulder representative of the port geometry seen in many burst disc and O-ring combinations rather than m-m seal, could also be made and tested at temperature.
Fig2: Detailed view of test cell port geometry
Burst disc Burst disc We can vary the bursting pressures by suitable choice of foil thickness and correction factors being applied. In the pictures shown is a burst disc in its post test state.
Fig3: Detailed views post test discs
Digial pressure read-out Pressures at these elevated levels are recorded by us in 5psi increments. At normal lower operating pressure levels the equipment is capable of reading-out in single psi figures. It is regularly calibrated to ensure consistency
Test cell temperatures within the oil bath are recorded both pre and post test - the average being the 'declared' temperature.
Fig4: Calibrated digital pressure read-out
In any given batch of burst discs Benoil policy is that to ensure statistical certainty a minimum of 5 samples be tested to ensure the repeatability of results before test certification is issued.
The Benoil normal tolerance rating on the declared burst pressure is ±5% of nominal. Test certification is supplied with each disc, showing the manufacturing date, batch date, the result of test bursts for that batch and the average batch pressure therefore.

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