Introduction
Proof-of-design test, which is done once and is repeated only after a change of design. The manufacturer of ductile iron pipes has the responsibility of carrying out type tests to demonstrate the conformity of the products with the International Standards (ISO 2531:2009/EN 545:2010 for water application and ISO 7186:2011/EN 598:2009 for sewerage application).
Requirements of type tests
There shall be a type test for at least one DN for each of the groupings given in the table below:
List of type tests performed on DI pipe joints
- Leak tightness of joints to hydrostatic pressure
- Leak tightness of joints to positive internal pressure
- Leak tightness of joints to positive external pressure
- Leak tightness of joints to negative internal pressure
- Leak tightness of joints to dynamic internal pressure
- Leak tightness and mechanical resistance of flanged joints
Methodology of various type tests
Leak tightness of joints to positive internal pressure
The leak tightness of joints to internal pressure shall be type tested at a pressure of 1.5PFA + 5 bar. The test assembly shall be filled with water and suitably vented of air. The pressure shall be raised steadily until it reaches the test pressure; the rate of pressure increase shall not exceed 1 bar/s. The test pressure shall be kept constant within ± 0.5 bar for at least 2 h, during which the joint shall be thoroughly inspected every 15 minutes.
Leak tightness of joints to positive external pressure
The leak tightness of joints to external pressure shall be type tested at a pressure not less than 2 bar. The joint shall exhibit no visible leakage when subjected to a shear load, expressed in newton, not less than 30 times DN. The test assembly shall be subjected to the shear load; one-half of this load shall be applied to the spigot on each side of the test assembly, by means of a V-shaped block with an angle of 120°, located at approximately 0.5 x DN, in millimeters, or 200 mm from the end of sockets (whichever is the greater); the sockets shall bear on a flat support. The test assembly shall then be filled with water and suitably vented of air. The pressure shall be steadily increased until it reaches the test pressure given above and then kept constant within ± 0.1 bar for at least 2 h, during which the internal side of the joint subjected to external pressure shall be thoroughly inspected every 15 minutes.
Leak tightness of joints to negative internal pressure
The test assembly shall be empty of water and shall be evacuated to a negative internal pressure of 0.9 bar and then isolated from the vacuum pump. The test assembly shall be left under vacuum for at least 2 h during which the pressure shall not have changed by more than 0.09 bar. The test shall begin at a temperature between 5 °C and 40 °C. The temperature of the test assembly shall not vary by more than 10 °C for the duration of the test.
Leak tightness of joints to dynamic internal pressure
The test assembly and test apparatus shall be as given for positive internal pressure. The test assembly shall be filled with water and suitably vented of air. The pressure shall be steadily increased up to PMA, the allowable maximum operating pressure of the joint, and then automatically monitored according to the following pressure cycle:
- steady pressure reduction to (PMA – 5) bar;
- maintain (PMA – 5) bar for at least 5 s;
- steady pressure increase to PMA;
- maintain PMA for at least 5 s.
The type tests are carried out either by the manufacturer or, at his request, by a competent testing institute in order to demonstrate compliance with the requirements of the International Standards. Full reports of these type tests are retained by the supplier of pipes, fittings and gaskets as evidence of compliance. If fittings or gaskets are supplied separately from pipes, full reports of the type tests on these components, and their compatibility with pipes, shall be made available to the client by the fitting or gasket suppliers. If the design has been tested and documented by the manufacturer and successfully used for a minimum of 10 years, the performance of a type test as specified for internal pressure, as specified for external pressure and as specified for negative internal pressure, is only required for significant changes in design which could adversely affect the performance of the joint (Cl. 5.2.1 ISO 2531:2009).
Sabarna Roy, Senior Vice President, Basanta Bera, Assistant Manager
Business Development, Electrosteel Castings Limited