Multiphase Valve Testing

1. Field of the Invention

This invention relates to apparatus and a method for testing valves, and more particularly, for set point and seat leakage testing of pressure relief valves with selected fluids in selected phases.

2. Background Information

Set point testing of relief valves is required by the American Society of Mechanical Engineers (Sections III, VIII) to assure that vessels, boilers and pipelines are not overpressurized. To accomplish this, two schemes are generally used, viz:

(1) one approach is to remove the valve to be tested from the protected equipment and test it in a shop with water, nitrogen or steam, as available. Nitrogen is commonly used because it is generally available.

(2) another technique is to leave the relief valve in place on the protected equipment and to install on top of the valve an assist device, typically pneumatic or hydraulic powered, that will aid the valve to open. By monitoring system conditions in the output of the assist device, it is possible to back calculate the set point of the relief valve.

While the above schemes are generally acceptable, there is always a desire among maintenance and operations people, to test relief valves for set point and leakage in the actual medium and conditions in which they are used to confirm their operational readiness. For example, set point testing of relief valves used in steam service with nitrogen is permissible, but there is no reliable correlation that converts the test results in one medium to another. Similarly, the use of power assist devices introduces some uncertainty in data reduction in terms of the interaction of the displacements of many interacting valve parts on the estimated set point. Since the set point is back calculated when power assist devices are used, the accuracy of the final result depends upon the precision of the recorded variables. Thus, while the present test schemes are acceptable, they can still be improved upon.

In accordance with the invention, a relief valve is tested using a test device which includes a housing defining an internal chamber which is divided into a test chamber and a pressurizing chamber by piston means. Preferably, the piston means includes a main piston which forms an end wall of the test chamber, a translator piston which forms an end wall of the pressurizing chamber, and a spring pack in the form of a helical compression spring between the two pistons. The relief valve to be tested is bolted to an adapter plate having a hole pattern adapted to receive various sizes of relief valves with the inlet of the relief valve in communication with the test chamber. A selected test medium is introduced into the test chamber and relief valve through an inlet pipe while air is vented through a diametrically displaced vent pipe. Once the test chamber and relief valve are filled with the selected test medium, an inlet valve in the inlet line and a vent valve in the vent line are closed, and pressurizing fluid is introduced into the pressurizing chamber. Movement of the translator piston in response to the introduction of pressurizing fluid into the pressurizing chamber compresses the spring pack to load the main piston. The pressure in the test chamber is increased by increasing the pressure in the pressurizing chamber until the relief valve actuates. The set point of the relief valve is checked against the pressure in the test chamber at which the valve actuates as indicated by a pressure guage, preferably connected in the vent line.

If a hot liquid test is desired, an electric immersion heater in the test chamber heats the fluid medium to the desired temperature. If vapor testing is desired, the temperature of the test fluid in the liquid state is increased with system pressure set lower than the desired test pressure, at a pressure just above, but close to, the pressure required to maintain the test fluid in the liquid state at the desired test temperature. Once the desired temperature is reached, system pressure is rapidly reduced causing the liquid to flash into vapor. Preferably, this rapid reduction in pressure is achieved through a rapid increase in the volume of the test chamber induced by a reduction in the pressure of the pressurizing fluid. Following flashing of the test fluid to the vapor state, the pressure is quickly built up to the desired test pressure by again increasing the pressure of the pressurizing fluid. When the pressure has stabilized it is then slowly increased further until the relief valve actuates.

The apparatus and method of the invention offer many advantages in the testing of relief valves. With the invention, a relief valve may be tested using different fluids in one set up. Testing can be conducted at various fluid temperatures and in their gaseous or liquid phase. Discharge of test fluid is minimized so that toxic fluids can be safely handled and vented. The device is portable and can be used to test more than one size valve using the same fixture. Furthermore, no correlation factors are required. The actual data can be recorded as representative of valve behavior.

A full understanding of the invention can be gained from the following description of the preferred embodiment when read in conjunction with the accompanying drawings in which:

FIG. 1 is a longitudinal section through the relief valve test device according to the invention;

FIG. 2 is a plan view of the an adapter plate by which relief valves of varying sizes may be secured to the device of FIG. 1; and

FIG. 3 is an elevation view of the test device of FIG. 1 with a relief valve secured thereto for testing.

As shown in the Figures the valve testing device 1 of the invention comprises a cylindrical housing 3 having a longitudinal bore 5 which defines an elongated chamber 7. The elongated chamber 7 is closed at one end by an endplate 9 secured by nuts and bolts 11 to flange 13 welded at 15 to the housing 3. Another flange 17 is welded at 19 to the other end of the housing 3, and an adapter plate 21 is secured to this flange by studs and nuts 23 (see FIG. 3). As illustrated in FIG. 2, the adapter plate 21 is provided with bolt holes 25 arranged in a pattern which accepts various sizes of relief valves. As shown in FIG. 3, a relief valve 27 is bolted by bolts 29 to the adapter plate 21 for testing.

A piston assembly 31 slidable in the bore 5 of the housing divides the elongated chamber 7 into a test chamber 33 and a pressurizing chamber 35. This piston assembly 31 includes a main piston 37 forming an end wall of the test chamber 33 and a translator piston 39 which forms one end wall of the pressurizing chamber 35. Between the main piston 37 and translator piston 39 is a spring pack 41 comprising a helical compression spring.

An inlet pipe 43 and vent pipe 45 penetrate the wall of housing 3 at diametrically opposed locations for feeding and venting, respectively, the test chamber 33. An inlet valve 47 and vent valve 49 selectively block off the inlet pipe 43 and vent pipe 45 respectively. Connected to the vent pipe 45 are pressure measuring accessories in the form of pressure guage 51 for direct reading of the test chamber pressure and pressure transducer 53 for transmitting pressure signals to a pressure control device (not shown). Four equiangularly spaced travel stop buttons 55 (only three shown) extending inward through the wall of the housing 3 limit the travel of the piston assembly 31 in the direction of the test chamber 33 so that the inlet and vent pipes are not blocked by the piston.

Primary leak tightness for the main piston is provided by the pair of "O" ring seals 57 seated in annular grooves 59 in the piston. A secondary or back-up seal is provided by a pair of packing rings 61 seated in a groove 63 and held in place by a packing flange 65 and packing bolts 67. The translator piston 39 is sealed by "O" ring seals 69 seated in grooves 71. The end plate 9 is sealed against flange 13 by gasket 73. Similarly, the adapter plate 21 is sealed against flange 17 by gasket 75. The space 77 between pistons 37 and 39 is vented by orifice 79 through which any leakage from the test chamber 33 or pressurizing chamber 35 is removed. A rod 81 threaded into the main piston 37 and held in place by a lock nut 83, provides a controlled travel limit on the displacement of the translator piston 39 so that excessive displacement which would initiate the collapse of the spring pack 41 will not occur. Additionally, this rod 81 serves as a guide for spring pack 41.

An electric immersion heater 85 extends through the housing 3 into the test chamber 33 for heating the test medium for certain tests as discussed below. Thermocouples 87 are also provided in the test chamber for measuring the temperature of the test medium.

A nipple 89 is centrally located in endplate 9 for connecting a hose 91 for admitting and venting a pressurizing fluid supplied by a pressurized fluid source 92 into the pressurizing chamber 35 to provide the motive force to pressurize test fluid in the test chamber 33.

A relief valve 27 to be tested is bolted to the adapter plate 21 as shown in FIG. 3 with the inlet of the valve in communication with the test chamber 33 through a central bore 93 in the adapter plate. The test device can be supported with the relief valve in any orientation desired such as by the supports 95 in FIG. 3. The desired test fluid is admitted into the test chamber 33 and relief valve 27 through inlet pipe 43 by opening inlet valve 47. Any air in test chamber 33 is vented out through vent pipe 45 by opening vent valve 49. The test device 1 may be rotated to assure that all the air is removed. Once the test chamber 33 is filled with test fluid, the inlet pipe 43 and vent pipe 45 are blocked by closing valves 47 and 49 respectively. A high pressure fluid (such as air, water or oil) is introduced into pressurizing chamber 35 and bears against the translator piston 39 causing it to move. The motion of the translator piston 39 compresses the spring pack 41 which in turn loads the main piston. The main piston compresses the test fluid trapped in test chamber 33. By increasing the pressure of the pressurizing fluid, the pressure of the test fluid is increased until the relief valve set point pressure is reached and the valve pops. By monitoring the pressure on the pressure guage 51 the accuracy of the set point setting can be tested.

If the temperature of the test medium is to be increased (for example, a hot liquid test is desired), the heaters 85 are turned on and the temperature of the test fluid is controlled by means of thermocouple 87 output. Thermal pressurization is minimized by the fact that the spring pack 41 compresses as pressure in the test chamber 33 increases, thus reducing the likelihood of a thermally induced pressure build up in the chamber. Testing proceeds by increasing the pressure of the hydraulic fluid in pressurizing chamber 35 until the valve test pressure is reached and the valve 27 pops. If the temperature is increased to the point where the rod 81 seats against the translator piston 39, further increase in the pressure in the test chamber 33 can be precluded by utilizing a constant pressure pressurized fluid source 92 for supplying fluid to the pressurizing chamber 35. In fact, the translator piston 39 could alternatively be fixed to the main piston 37 such as by a rod 81 secured to both pistons. In this case, a constant pressure source of pressurized fluid should be used to minimize pressure build up in the test chamber during hot testing.

If testing in a vapor state is desired, the temperature of the fluid in the liquid state is increased with system pressure set lower than the desired test pressure, at a pressure just above, but close to, the pressure required to maintain the test fluid in the liquid state at the desired test temperature. For example, if the test is to be run on steam at 2,500 psi and 650 degrees F., the test fluid pressure is set at 2,300 psi which has a saturation temperature of 655.89 degrees F. Heat is applied to the test fluid until the desired temperature of 650 degrees F. is reached. Once this temperature is reached, the test pressure is suddenly reduced (for example, from 2,300 psi to 1,000 psi) causing the test fluid to flash into a vapor state. The test pressure is suddenly reduced by increasing the volume of the test chamber 33 through movement of the piston assembly 31 in response to a sudden reduction in the pressure of the pressurizing fluid supplied to the pressurizing chamber 35. Following the flashing of the test fluid, the test pressure is quickly built up to the test condition (i.e. 2,500 psi) by increasing the pressure of the hydraulic fluid supplied to chamber 35. Once the desired pressure is reached, it is allowed to stabilize in accordance with the desired test instructions. Since condensation form a vapor state to a liquid state condition is a slow thermodynamic process, the test medium will remain in a vapor state for a considerable time allowing sufficient time for testing to be conducted. By gradually increasing the pressure, the valve will pop at its set point in the desired test medium.

Pressures and temperatures are monitored by means of the thermocouples 87 and pressure transducers 53. The adapter plate 21 in addition to providing means to adapt the device 1 to various relief valve 27 also provides a means to mount and move the assembled device such that it can be positioned in a most convenient way for the test.

While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.