Hydrostatic Pressure Testing is a nondestructive testing (NDT) method of finding leaks or verifying performance and durability in pressure vessel such as pipe, tubing, and coils. Although this is considered nondestructive testing and failures are rare, they can occur when the test piece does not meet performance or durability specifications and may render the piece unusable.
Hydrostatic Pressure Testing usually entails filling the pipe, tubing, or coil with liquid, bleeding out air, pressurizing the piece, and then examining it for leaks or permanent changes in shape. A nearly incompressible (compressible only by weight, not air pressure) liquid, usually water or oil, is used to fill the test piece because it will only expand by a very small amount if the piece fails, and therefore, minimizes the chance of injury or further damage. Hydrostatic pressure testing also can be performed with pressurized air, but is generally completed with the vessel under water for safety reasons. Although a testing laboratory may be equipped to perform hydrostatic pressure testing with water, oil, or air under water, water is the most commonly used test medium because it is less expensive than oil and easier to set up than air under water.
This nondestructive testing method is used to test tubing, pipe and coils to pressures measured in PSI (e.g. to 10,000 PSI). The amount of pressure used in hydrostatic pressure testing is always considerably more than the operating pressure, or the pressure the vessel will be subjected to in the course of operation, to give the customer a margin for safety. Typically the test is performed at 150 percent of the design or working pressure. For example, if a pipe was rated to a working pressure of 2000 PSI, it would be tested at 3000 PSI.
Worldwide fabricators who supply the oil, gas and petrochemical industry, require the highest specification steels for use in the manufacture of weldable steel pressure vessels and industrial boilers. 16Mo3, which is supplied under the EN 10028 euro norm specification, is one of these steels.
16Mo3 is a chrome molybdenum based steel which has excellent heat resistance and corrosion resistant characteristics. For these reasons alone, the steel is a popular in the manufacture of pressurised vessels and boilers. The material offers good welding properties when using conventional welding methods and due to the materials excellent heat resistance, 16Mo3 is also used in pipework for transporting hot liquids.
Added chromium in the steel increases the corrosion resistance whilst the higher molybdenum content promotes the increase in resistance to elevated temperatures. 16Mo3 also has good hot and cold forming properties and is normally delivered in 'as rolled' condition. Consideration should be made concerning the level of tensile strength required before procuring 16Mo3 - whilst the material offers good overall tensile strength, this strength decreases as the temperature rises.
Equivalents for this steel grade can be found under both the ASTM and ASME steel specifications for chrome moly (A387 and SA387 respectively).
Key benefits of 16Mo3 chrome moly steel
- Excellent heat and corrosion resistance
- Good welding properties
- Good tensile and yield strength
- Good fatigue and wear resistance
- Toughness
16Mo3 is also extensively used by the inshore and offshore industry. Material of this type normally comes with mill certification and stamping and further testing is normally supplied on the customers request. This can be done by a third party testing house or independently inspected by the customer.
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