PROCEDURE TWO-PLY TESTABLE BELLOWS D 1 OF 5 TWO PLY BELLOWS TEST PROCEDURE

Transcription

1 PROCEDURE TWO-PLY TESTABLE BELLOWS D 1 OF 5 TWO PLY BELLOWS TEST PROCEDURE Prepared by: Pathway Piping Solutions Daniel L. Edgar, PE Pine Valley, Ca Phone: (619) FAX: (619) Pathway Administrative Offices 115 Franklin Road Oak Ridge, Tn Customer Service Representative: Jeff Searle Phone: (615) ex 170 FAX: (615) July 14, 2008 Rev D

2 PROCEDURE TWO-PLY TESTABLE BELLOWS D 2 OF 5 PURPOSE A two ply bellows element is may be test to confirm that both the inner and outer plies are operating properly. A two ply testable bellows test is NOT a proof test intended to test the bellows or welds to their maximum capacity. It is a low pressure boundary continuity leak test. Therefore, the test pressure is limited to between psig. It is intended to confirm there is no leak on the outside surface and inside surface and the two attachment welds. The boundary is check by pressurizing the area between the plies, that isolating the area and watching for a decay in the pressure in the isolated area. If the bellows fails to maintain pressure, an air & soap bubble inspection can be made of exterior surfaces and attachment weld to determine the source the leak. TWO PLY THEORY The standard bellows consists of single ply of relatively thin, to and is subject to failure without notice. Due to the critical nature of expansion joints, the industry has developed the two ply testable bellows, which will provide advance warning of failure on the interior surfaces. When a two ply testable bellows is design, Pathway will design a single ply to withstand all operating pressures, temperatures and movements. When the design is complete, a second redundant ply is added, see figure 1. The two plies are separated by an interior wire mesh, which allows a gas media to flow through the interior area. Finally, a monitoring tube is added to the outer ply thus allowing the interior area to be monitored. In the event that the inner ply fails, the operating pressure will pressurized the interior area and the monitoring tube. This tube is normally equipped with a device, which is capable of detecting this pressure and warning the operators. The operators can then take action depending on how long the unit has been in service. If the unit is relatively new, then immediate action might be called for, however, if the unit has been in service for a considerable amount of time, then it is probably acceptable to what until the next scheduled shut down. In any event, the Pathway facility should be consulted in the event of a failure. Pathway equips most two ply bellows with RED TOPS, which monitor the interior area. In the event of an inner ply lead, the RED TOP will pop up indicating this failure. Since the interior area is a closed gas area, it is possible for the air between the plies to become heated by operation, expand and give a false reading. Therefore, prior to any action, unscrew the RED-TOP and then screwing it back down should depressurize the area..

3 PROCEDURE TWO-PLY TESTABLE BELLOWS D 3 OF 5

4 PROCEDURE TWO-PLY TESTABLE BELLOWS D 4 OF 5 TWO PLY TEST PROCEDURE INSPECT THE BELLOWS Prior to testing a bellows, it should be inspected for deformities, instability and cracks. The bellows monitoring tube should also be inspected for cracks. The bellows should be of a smooth, symmetrical pattern. Some bellows are preset to be deflected in the cold condition, therefore, the convolutions may not be in the neutral condition during a cold inspection. If any indications are noted, the inspector should contact Pathway prior to testing the bellows. SET UP TEST EQUIPMENT The general configuration of a red-top is shown by Figure 1 and photo 1. The equipment needed for this test is depicted by figure 2. Nitrogen is recommended as the test media, however, any inert gas may be used. Also, instrument quality air may also be used. The intent is to limit contaminates or moisture from being introduced into the bellows interior area. A twostage pressure regulator must be used to prevent the bellows from becoming over pressurized. It is also recommended that low-pressure plastic tubing be used to connect the pressure regulator to the isolation valve. In this way, the tube will blow out prior to the bellows. CHECK PRESSURE The first step in testing the bellows is to assure that there is no pressure between the plies. First check to assure that the Red-Top indicator button is not popped up. The indicator is located on the top of the Red- Top, is red in color and should be flush with the canister. If it is not, contact the facility engineer. If the pressure indicator is down, then you should check to assure that there is no pressure between the plies by opening the purge valve located below the Red-Top, see photo-2 & 3. Open this valve for approximately 2 minutes then shut the valve tightly.

5 PROCEDURE TWO-PLY TESTABLE BELLOWS D 5 OF 5 PEPARING THE TEST PORT PIPE Once the Red-Top has been removed, the threaded part of the test port should be thoroughly cleaned with a stainless steel wire brush. All old Teflon tape and corrosion should be removed, see photo- 5. Once cleaned, Teflon plumbers tape should be applied to the threads. The tape should be applied in a clockwise direction and approximately 5 or 6 layers is recommended, see photo-6. REMOVE THE RED-TOP / PRESSURE GAGE Most two ply testable bellows are equipped with some means of monitoring the interior area. The RED TOP is supplied by Pathway, see photo 4, and may be unscrewed from the monitoring tube. In some cases, the customer has installed pressure gages or monitoring systems to the monitoring tube. In this event, it is recommended that the bellows be tested with an attachment as close to the bellows as possible. It is not uncommon for systems to lose pressure as the result of leaking instrument tubing or faulty piping systems. Any equipment / device removed from the bellows should be temporarily sealed to prevent contaminates from entering the components. INSTALL PRESSURE GAGE The test rig consists of a pipe union, pressure gage and isolation valve. The rig should be installed and wrenched down to a tight fit. The pressure gage should be visible from the scaffold / deck. Once the rig is installed, the isolation valve should be closed to prevent the possibility of over pressurizing the bellows, see photo-7.

6 PROCEDURE TWO-PLY TESTABLE BELLOWS D 6 OF 5 SETUP THE GAS BOTTLE The two-stage pressure regulator should installed on the gas bottle and wrenched tight. Then, the gas bottle should be turned on. Verify that there is sufficient pressure in the gas bottle to perform the test, 30 psig minimum. Install the plastic tubing between the regulator and the test rig. Turn on the regulator and adjust the regulator to a constant pressure of 10 to 15 psig, see photo-8 & 9. The pressure should be maintained for approximately 5 minutes to assure that the two stage pressure regulator is operating properly. the isolation valve to remain open for approximately 15 minutes. While the bellows is pressurizing, an air and soap bubble test should be performed to confirm that all connections are gas tight, see photo-10. If the bellows is equipped with a flow monitoring tube, normally located on the opposite side of the bellows, make sure that the gas is flowing freely through the tube and then close the flow monitoring tube valve. PRESSURE DECAY TEST Once the bellows has been pressurized, close the isolation valve and record the starting pressure from the monitoring pressure gage and record the start time. The bellows should maintain pressure over a period of 15 to 20 minutes. There should be no pressure reduction over the test period. OPEN ISOLATION VALVE The bellows interior area may now be pressurized by opening the isolation valve and allow the pressure to saturate the bellows interior area. The interior area will expand when pressurized, therefore, allow

7 PROCEDURE TWO-PLY TESTABLE BELLOWS D 7 OF 5 EVALUATING PRESSURE DROP - In the event that the pressure begins to drop pressure, open the isolation valve and re-pressurize the bellows to confirm that the pressure lose is not the result of the interior area expanding due to pressure. Repeat this step several times prior to proceeding to the next step. While re-pressurizing, repeat the air & soap bubble test of the test rig and the second port on the back side of the bellows, if applicable. 1) QUICK DROP OFF - If the pressure continues to drop, then it is likely that there is a leak in the outer ply and/or attachment weld or two-ply test port. If the pressure is dropping quickly, less then a minute, and it drops to zero, then it is most likely a crack in the outer ply / attachment weld. If this is a cold test, then the crack should be located by by air and soap bubble testing of the bellows. Normally there is no access to the interior of the bellows and therefore inspection of the interior is not possible. In the event that the location of the leak can not be found, Pathway should be contacted. 2) SLOW DROP OFF - If the pressure drops slowly, over a minute, to a constant pressure, then it is likely that there is a thread leak in the test port or a pinhole leak in the attachment weld. If this is a cold test, then the test port and attachment welds should be air and soap bubble tested to locate the leak. A slow leak may be acceptable because it does not impair the capability of the two ply bellows. An inner ply leak would over power the leak and still provide early warning capability and therefore my continue in service. REINSTALLING THE RED TOP / PRESSURE GAGE - Once the bellows has passed the pressure decay test, all test equipment should be broken down and the original RED- TOP / pressure gage / monitoring system should be reinstalled. Prior to installing the components, the bellows should be allowed to depressurize by allowing the monitoring tube to remain open for approximately 10 minutes. Then the component should be cleaned and reinstalled using Teflon plumbers tape.

8 NPTPipe x ¼ UNFTube (Compression). Male Pipe x Tube Adapter ¼ brass NPTmale to NPTmale adapter fitting ¼ ball valve, NPTfemale to NPT female ¼ brass Tee, NPT female to NPT female fitting NPTPipe x ¼ UNFTube (Compression). Male Pipe x Tube Adapter Pressure Regulator Pressure Regulator Adapter Fitting Compressed Air Dryer Electrical Air Compressor ¼ NPTPipe x ¼ UNFTube (Compression). ¼ NPTPipe x ¼ Male Pipe x Tube Adapter ¼ NPTPipe x ¼ UNFTube (Compression). Female Pipe x Tube Adapter UNFTube (Compression). Male Pipe x Tube Adapter Top bellows connection Bottom bellows connection

9 Electrical Air Compressor ¼ brass Tee, NPTfemale to NPTfemale fitting Pressure Gauge Compress Air Dryer (Compression). Male Pipe x Tube Adapter Pressure Regulator (Compression). Male Pipe x Tube Adapter ¼ Polyethylene Tubing (Compression). Male Pipe x Tube Adapter Bellows Test Port ¼ Polyethylene Tubing (Compression). Female Pipe x Tube Adapter (Compression) ¼ ball valve, NPTfemale to NPTfemale ¼ brass NPTmale to NPTmale adapter fitting ¼ Polyethylene Tubing (Compression). Male Pipe x Tube Adapter ¼ brass Tee, NPTfemale to NPTfemale fitting ¼ brass NPTmale to NPTmale adapter fitting Pressure Gauge ¼ ball valve, NPTfemale to NPTfemale

10 Gauge Type: Pressure Service Type: General Service For Use With Compressed Air, Ethyl Alcohol, Hydraulic Oil, Nitrogen, Water Accuracy: ±2% Mid-Scale (Grade B) NIST Certification: Without Certificate of Calibration Dial Type: Dry Connection Size and Type: 1/4" NPT Male Connection Location: Bottom Connection Material: Brass Sensor Type: Bourdon Pressure Tube Sensor Material (Internals): Bronze Case Material: Type 304 Stainless Steel Lens Material: Polycarbonate Units of Measure: psi Operating Pressure Range (psi): 0 to 60 Numeral Increments (psi): 10 Graduation Marks (psi): 1 Round Dial Diameter: 2-1/2" Process Temperature Range: -40º to +150º F Ambient Temperature Range: -40º to +150º F Specifications Met: American Society of Mechanical Engineers (ASME) ASME Specifications Met: B40.1 Shape: Pipe to Tube Adapter Pipe to Tube Type: Male Pipe x Tube Adapter Compression Tube Fitting Type: General Purpose Pipe to Tube Connection: NPTPipe x UNFTube (Compression) System of Measurement : Inch Pipe/Thread Size: 1/4" Nut/Tube End Thread: 7/16"-24 For Tube OD: 1/4" Material: Yellow Brass Maximum 73 F: 90 psi Operating Temperature Range: -65 to +250 F For Tubing Type: Polyethylene For Use With: Air Tube Supports : Included Sleeve: Delrin Specifications Met: Not Rated Notes: Includes a body, nut, sleeve (ferrule), and a built-in stainless steel tube support that slips inside the tubing to prevent collapsing.