Kinds

Requirements

Explosion test process

(1) All explosion tests to verify the functionality of crankcase explosion relief valves are to be carried out us- ing an air and methane mixture with a methane concentration of 9.5 % ±0.5 %. The pressure in the test vessel is to be not less than atmospheric and not exceed 0.2 bar.

(2) The concentration of methane in the test vessel is to be measured in the top and bottom of the vessel and is not to differ by more than 0.5%.

(3) The ignition of the methane and air mixture is to be made at the centreline of the test vessel at a position approximately one third of the height or length of the test vessel opposite to where the valve is mounted.

(4) The ignition is to be made using a maximum 100 joule explosive charge.

Test vessel for explosion testing

(1) The test vessel for explosion testing is to have documented dimensions. The dimensions are to be such that the vessel is not "pipe like" with the distance between dished ends being not more than 2.5 times its diameter. The internal volume of the test vessel is to include any standpipe arrangements.

(2) The pressure measuring equipment is to be capable of measuring the pressure in the test vessel in at least two positions, one at the valve(P2 in Fig 3.9.1) and the other at the test vessel centre(P1 in Fig 3.9.1). The measuring arrangements are to be capable of measuring and recording the pressure changes throughout an explosion test at a frequency recognising the speed of events during an explosion. The result of each test is to be documented by video recording and if necessary by recording with a heat sensitive camera.

(3) The test vessel is to be provided with a flange, located centrally at one end perpendicular to the vessel longitudinal axis, for mounting the explosion relief valve. The test vessel is to be arranged in an ori- entation consistent with how the valve will be installed in service, i.e., in the vertical plane or the hori- zontal plane.

Kinds

Requirements

Test vessel for explosion testing

(4) A circular plate is to be provided for fitting between the pressure vessel flange and valve to be tested with the following dimensions:

a) Outside diameter of 2 times the outer diameter(D2 in Fig 3.9.1) of the valve top cover.

b) Internal bore having the same internal diameter(D1 in Fig 3.9.1) as the valve to be tested.

(5) The test vessel is to have connections for measuring the methane in air mixture at the top(G2 in Fig 3.9.1) and bottom(G1 in Fig 3.9.1).

(6) The test vessel is to be provided with a means of fitting an ignition source at a position approximately one third of the height or length of the test vessel opposite to where the valve is mounted.

(7) The test vessel volume is to be as far as practicable, related to the size and capability of the relief valve to be tested. In general, the volume is to correspond to the requirement for the free area of explosion relief valve to be not less than 115 cm m of crankcase gross volume. This means that the testing of a valve having 1150 cm of free area, would require a test vessel with a volume of 10 m . Where the free area of relief valves is greater than

115 cm m of the crankcase gross volume, the volume of the test vessel is to be con- sistent with the design ratio. In no case is the volume of the test vessel to vary by more

than +15% to -15% from the design cm m volume ratio.

(8) The test facilities are to have equipment for controlling and measuring a methane gas in air

concentration within a test vessel to an accuracy of ± 0.1%.

Explosion testing

General

(1) Where valves are to be installed on an engine or gear case with shielding arrangements to deflect the emission of explosion combustion products, the valves are to be tested with the shielding arrangements fitted.

(2) Successive explosion testing to establish a valve's functionality is to be carried out as quick- ly as possible during stable weather conditions.

(3) The pressure rise and decay during all explosion testing is to be recorded.

(4) The external condition of the valves is to be monitored during each test for indication of any flame release by video and heat sensitive camera.

(5) For obtaining the type approval, the explosion testing for each valves shall be done for

three stages respectively.

Stage 1

Two explosion tests are to be carried out with the flange opening fitted with the circular plate covered by a 0.05 mm thick polythene film. These tests establish a reference pressure level for determination of the effects of a relief valve in terms of pressure rise in the test vessel.

Stage 2

(1) Two explosion tests are to be carried out on three different valves of the same size. Each valve is to be mounted in the orientation that it requires approval for installation i.e., in the vertical or horizontal position with the circular plate located between the valve and pressure vessel mounting flange.

Kinds

Requirements

Explosio n testing

Stage 2

(2) The first of the two tests on each valve is to be carried out with a 0.05mm thick poly- thene bag, having a minimum diameter of three times the diameter of the circular plate and volume not less than 30% of the test vessel, enclosing the valve and circular plate. Before carrying out the explosion test the polythene bag is to be empty of air. The poly- thene bag is required to provide a readily visible means of assessing whether there is flame transmission through the relief valve following an explosion. (During the test, the explosion pressure will open the valve and some unburned methane/air mixture will be collected in the polythene bag. When the flame reaches the flame arrester and if there is flame transmission through the flame arrester, the methane/air mixture in the bag will be ignited and this will be visible.)

(3) Provided that the first explosion test successfully demonstrated that there was no indication of combustion outside the flame arrester and there are no visible signs of damage to the flame arrester or valve, a second explosion test without the polythene bag arrangement is to be carried out as quickly as possible after the first test. During the second explosion test, the valve is to be visually monitored for any indication of combustion outside the flame arrester and video records are to be kept for subsequent analysis. The second test is required to demonstrate that the valve can still function in the event of a secondary crankcase explosion.

(4) After each explosion, the test vessel is to be maintained in the closed condition for at least 10 seconds to enable the tightness of the valve to be ascertained. The tightness of the valve can be verified during the test from the pressure/time records or by a separate test after completing the second explosion test.

Stage 3

Carry out two further explosion tests as described in Stage 1. These further tests are required to provide an average base line value for assessment of pressure rise recognising that the test vessel ambient conditions may have changed during the testing of the explosion relief valves in Stage 2.

Assessment and records

(1) The valves to be tested are to have evidence of design appraisal/approval by the Society

(2) The designation, dimensions and characteristics of the valves to be tested are to be recorded. This is to include the free area of the valve and of the flame arrester and the amount of valve lift at 0.2bar.

(3) The test vessel volume is to be determined and recorded.

(4) For acceptance of the functioning of the flame arrester there is not to be any indication of flame or combustion outside the valve during an explosion test. This should be con- firmed by the test laboratory taking into account measurements from the heat sensitive camera.

(5) The pressure rise and decay during an explosion is to be recorded, with indication of the

pressure variation showing the maximum overpressure and steady underpressure in the test vessel during testing. The pressure variation is to be recorded at two points in the pres- sure vessel.

(6) The effect of an explosion relief valve in terms of pressure rise following an explosion is

ascertained from maximum pressures recorded at the centre of the test vessel during the three stages. The pressure rise within the test vessel due to the installation of a relief valve is the difference between average pressure of the four explosions from Stages 1 and

3 and the average of the first tests on the three valves in Stage 2. The pressure rise is not to exceed the limit specified by the manufacturer.

(7) The valve tightness is to be ascertained by verifying from the records at the time of test- ing that an underpressure of at least 0.3bar is held by the test vessel for at least 10 sec- onds following an explosion. This test is to verify that the valve has effectively closed and is reasonably gas-tight following dynamic operation during an explosion.

(8) After each explosion test in Stage 2, the external condition of the flame arrester is to be examined for signs of serious damage and/or deformation that may affect the operation of the valve.

(9) After completing the explosion tests, the valves are to be dismantled and the condition of all components ascertained and documented. In particular, any indication of valve sticking or uneven opening that may affect operation of the valve is to be noted. Photographic re- cords of the valve condition are to be taken and included in the report.