Pressure testing

When constmction is complete, the pipeline must be tested for leaks and strength before being put into service industry code specifies the test procedures. Water is the test fluid of choice for natural gas pipelines, and hydrostatic testing is often carried out beyond the yield strength in order to reHeve secondary stresses added during constmction or to ensure that all defects are found. Industry code limits on the hoop stress control the test pressures, which are also limited by location classification based on population. Hoop stress is calculated from the formula, S = PD/2t, where S is the hoop stress in kPa (psig) P is the internal pressure in kPa (psig), and D and T are the outside pipe diameter and nominal wall thickness, respectively, in mm (in.). 

TABLE 10-46 Hydrostatic-Shell Test Pressures for FlangeS/ Flanged FittingS/ and Flanged Valves of Typical Materials ... 

Material group no. Shell test pressures hy class, Ihf/in gauge ... 

The hydrostatic-test pressure at any point in the system shall be as follows ... 

For a design temperature above the test temperature, the minimum test pressure shall be as calculated by the following formula ... 

If the test pressure as so defined would produce a stress in excess of the yield strength at test temperature, the test pressure may be reduced to the maximum pressure that will not exceed the yield strength at test temperature. 

A difference between tank cars and most pressure vessels is that tank cars are designed in terms of the theoretical ultimate or bursting strength of the tank. The test pressure is usually 40 percent of the bursting pressure (sometimes less). The safety valves are set at 75 percent of the test pressure. Thus, the maximum operating pressure is usually 30 percent of the bursting pressure. This gives a nominal factor of safety of 3.3, compared with 4.0 for Division 1 of the ASME Pressure Vessel Code. 

The DOT rules require that pressure cars have rehef valves designed to hmit pressure to 82.5 percent (with certain exceptions) of test pressure (110 percent of maximum operating pressure) when exposed to fire. Appendix A of AAR Specifications de s with the flow capacity of rehef devices. The formulas apply to cars in the upright position with the device discharging vapor. They may not protec-t the car adequately when it is overturned and the device is discharging hqnid. 

With all leaks stopped, and the reactor under test pressure with nitrogen, set the nitrogen pressure regulator to the lowest pressure on the controller, but above 0.3 atmosphere or 5 psig. Now open the flow controller and set the N2 flow to 66 mL/s, equivalent to 10.5 mols/hr rate, to start the flow. Also start heating the unit. 

Hydrostatie/pneumatie tests shall be performed on the main pressure-eontaining easings (inlet and exhaust) at a pressure of 1.5 times the maximum pressure. Temperature eompen-sation shall be applied where appropriate. Test pressure shall be maintained on the part for at least 30 min. Parts to be tested shall not be painted until testing is eomplete and satisfaetory. 

Design Pressure PSI Test Pressure PSi Design Temperature °F... 

The duration of the test pressure in most cases is 30 minutes mint-mum however, the test must be held for long enough beyond that time to permit a thorough examination for porosity and casing wall leakage. 

The hydrostatic testing is the first test used on the lube system. The system is tested while assembled or partially assembled, based on the particular system. A test pressure of VA times the maximum allowable working pressure, a minimum of 20 psi for the oil side, is used for the test. For the oil-wetted parts, the test fluid should be light oil, which is normally the recommended lubricant for the compressor train. The test period is the length of time needed to inspect for leaks, or a minimum ol thirty minutes. Acceptance is based on the lack of leaks as visually observed or the lack of a drop in the test pressure. 

Hoses to be indelibly marked to indicate the substances for which it is intended, its safe working pressure, proof-test pressure, date tested, and maximum or minimum service temperature. 

Cold Differential Test Pressure - The cold differential test pressure (in kPa gage) is the pressure at which the valve is adjusted to open on the test stand. This cold differential test pressure includes the corrections for service conditions of back pressure and/or temperature. 

The test pressure for class A ductwork should not exceed 1000 Pa or the maximum design static pressure, whichever is smaller. 

The test pressure should not be less than the design operating (static) pressure. 

Table 9.11 gives the upper limits of the leakage volume flow rate for the three ductwork classes at typical test pressures. 

TABLE 9.11 Maximum Leakage Factor for the Three Classes and for Typical Test Pressures... 

STANDARD LEAK TEST PRESSURE setting 3 PERCENT... 

It is possible that the employees concerned did not understand the difference between a pressure test, normally carried out with water, and a leak test, often carried out with compressed air at a pressure well below the test pressure. 

Standard Test Rig Test Gas Deflagrations Test Pressure Endurance Burn Test... 

Standard Test Pipe Test Gas Stable Detona- tion Over- driven Detona- tion Deflagra- tions Test Pressure Endur- ance Burn Test... 

Elsworth et al. (1983) report experiments performed in an open-topped channel 52 m long x 5 m high whose width was variable from 1 to 3 m. Experiments were performed with propane, both premixed as vapor and after a realistic spill of liquid within the channel. In some of the premixed combustion tests, baffles 1-2 m high were inserted into the bottom of the channel. Ignition of the propane-air mixtures revealed typical flame speeds of 4 m/s for the spill tests, and maximum flame speeds of 12.3 m/s in the premixed combustion tests. Pressure transducers recorded strong oscillations, but no quasi-static ovetpressure. 

The design overpressure of the vessel is 1.92 MPa, and the test pressure is 25% higher. Therefore, the absolute internal pressure p, is... 

Maimenance records such as critical instruiueni checks, pressure relief vah e tests, pressure vessel inspections... 

Establish field construction hydraulic test pressures for each process equipment. Sometimes the equipment is blanked or blocked off, and no test pressure is applied in the field, because all pressure equipment must be tested in the fabricators or manufacturers shop per ASME Code. 

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