TEST PROTOCOL VERIFICATION OF THE BEHAVIOUR OF A MECHANICAL COMPRESSION COUPLING DURING SETTLEMENT

Transcription

1 TEST PROTOCOL VERIFICATION OF THE BEHAVIOUR OF A MECHANICAL COMPRESSION COUPLING DURING SETTLEMENT Nova Siria factory, Roletto, April 6, 2011 Introduction Mechanical steel compression couplings (CC) are used to connect pipes of same or different type and material in straight or offset conditions. Depending on the type and characteristics, they are rated for axial deflections up to ±3 (total deflection 6 ) but they can be tailor made for larger deflections acting on the shape of the body and on the length. It is generally recognized that after the installation either in straight or deviated conditions the CC may/will accept angular deflections caused by external actions (settlements) without losing the tightness also if under pressure. It has been requested to Nova Siria a qualified supplier of steel compression couplings to prepare a test equipment to verify the behavior of the couplings during angular deflection and to test in my presence the deflection on an ND 1200 coupling. The test equipment has been realized in the Nova Siria factory and a first test has been performed successfully on April 6, The test has demonstrated that, after the connection of the pipes, the system accepts a significant deflection without presenting leaks. Test equipment The test equipment consisted in an adaptable steel frame, 8m long, with 2 vertical supports leaving a space of 4835 mm. The supports are reinforced in order to resist to a test pressure up to 10 bar. Each support is equipped with a hinge to which the closure end couplings of the pipes are connected. The pipe system has been designed as follows: 2 sections of GRP pipes, ND 1200, cross filament winding with inerts, STIS 5000 N/m 2, supplied by 2 ND 1200 steel end compression couplings (blind), standard Nova Siria design, PN 10. The couplings have been equipped with a frame to be connected with the hinge to permit the rotation in the vertical plane. At this stage it has been decided to prevent the rotation of the end joint in the horizontal plane. 1 ND 1200 compression coupling, standard WSP10SO with expanded length 653 mm and nominal length 590 mm ( 1 ), designed with ±25 mm tolerance on the diameter. The coupling length has been designed to permit a ±2,5 deflection with an initial spacing of 200mm between the pipe ends. The coupling has been equipped with 2 lateral supports, permitting the rotation of the coupling. The vertical displacement is obtained, if necessary, with pistons acting on the coupling. All tree couplings have been tightened with the standard torque recommended by Nova Siria for couplings with 10 bar rating. The value of the torque, applied with the cross bolting procedure and controlled with a dynamometric key, has been 80 N*m. 1 The nominal length is the length between the coupling s flanges when the coupling is tightened on the nominal external diameter Nova Siria compression coupling_test protocol - page 1 of 12

2 All gasket have been lubricated with Vaseline oil, to facilitate their sliding under compression. The system is intended to verify the reciprocal movement of the pipe and coupling under deflection and to verify that during the deflection there is no loss of tightness. Initial conditions The GRP pipe sections have been marked at a distance of 195 mm and 300 mm before installing the coupling. The design of the structure has been prepared in order to have a gap of 200 mm between the pipe spigots when installed. The resulting spacing, after fixing the pipe in the end couplings, has resulted as 203 mm in the top position ( 2 ). The coupling has been positioned centered with respect to the pipe ends, the open flanges resulting at 225 mm from the pipe ends. After tightening the coupling, supported, without internal pressure, the pipe resulted inserted for 145 mm from the gasket with the internal mark (195 mm) at 50 mm from the coupling s flanges. 2 All measures are referred to the top of the pipe + coupling arrangement. Nova Siria compression coupling_test protocol - page 2 of 12

3 The centering has been verified visually, taking into consideration that it was opportune to simulate also some imprecisions occurring in the field. Similarly, it has been checked that the gaskets were properly positioned. Also the pipe ends have been checked visually for deformation in the position of the compression flanges. As soon as the structure has been transported to open air, the filling has been started. The final filling length has been 4300 mm with an estimated volume calculated as 4,75 m 3. The first fill has been made at the pressure of industrial water network (around 0,8 bar). During the filling, air has been vented from the system and the fill has been left free to stabilize for a few hours. Water temperature has been 19 with an ambient temperature 23 under direct sun. Following the settlement of the internal pressure, the pressure has been increased with a hand piston pump at low flow rate, to permit the expansion of the pipe under pressure. The pressure has been then slowly increased to 6 bar, while venting the entrapped air. The increase in pressure has been followed with 2 manometers, recently calibrated, one with scale 0 6 bar and one with scale bar. The increase has been made in steps, letting sufficient time for stabilization. At the end of filling and pressurization, the bottom supports have been partially lowered 3 and the lateral supports have been slightly released, to simulate the operating conditions under pressure after a misaligned installation. The status of the 4 coupling connections has been observed without noticing any leak. The deflection (due to a slight misalignment of the supports) has been measured with the electronic level meters respectively as 0,7 left side, 0,4 right side (total 1,1 or ±0,55 ). A small movement of the pipe in the center coupling has been observed, while no significant movement of the pipe has taken place in the end couplings, due to the fact that the end coupling are free to rotate on the vertical axis. A minor decrease of the pressure has taken place due the deflection which causes an elongation of the system. The pressure has been restored to 6 bar, before continuing the lowering of the coupling. At this stage, the 4 bottom supports have been lowered fully, leaving space for the descent of the coupling, fixed only laterally by the 2 side pistons. 3 They have been kept near the pipe bottom to prevent a sudden collapse due to an eventual failure of the lateral pistons. Nova Siria compression coupling_test protocol - page 3 of 12

4 Lowering the lateral pistons, the pipe has been permitted to settle under own weight. At the stop of the settlement following data have been recorded (see drawing): Deflection left 2,8 ; Deflection right 3,1 ; total deflection 5,9 Coupling rotation 2,7 Due to the fact that there was no elastic support (simulating the soil resistance) the deflection has been accompanied by the movement of the lateral pistons to avoid a sudden collapse of the pipe + coupling. During the lowering, the position of the pipe marks has been observed, to avoid that during the movement one of the pipe spigots could slip out of the coupling s gasket. The lowering has been stopped while reaching 6 total axial deviation. The settlement has been interrupted to avoid the possible slippage of the pipe out of the coupling ( 4 ). It has been noted that the coupling follows the movement of the pipe. The movement has not been the same at the 2 ends; this is due to differences on the smoothness of the pipe surface and to the different hold of the gasket on the pipe. After the change in the length of the system due to the inclination, the pressure has decreased to 5,55 bar. No leak has been observed during and after the lowering. The pipe has been left in the position above for half hour, checking for eventual leaks and for movements of the gasket inside the coupling. After this settlement period, it has been decided to analyze what could happen if the coupling would be pushed up. This does not happen in the reality, unless there is an increase of the soil pressure under the pipe due to some geological movement. The coupling has been pushed up with a jack until it reached a position above the original one, both to observe the behavior of pipe and coupling and to verify again for leaks. The lifting has taken place at a slow ascent rate, but it is estimated that a quicker or slower lifting velocity would not have changed the situation. No leaks and no displacement of the gaskets have been observed. The final condition is shown here under: 4 The length of the coupling and the pipe insertion has been designed for a 5 total deflection, as mentioned previously. Nova Siria compression coupling_test protocol - page 4 of 12

5 Left pipe +1,0 Right pipe +0,4 Coupling 5,3 to the right, changing from the previous 2,7 In this case, again the 2 sections of pipe have behaved differently, due likely to small differences in tightness and in the pipe surface quality. Also, the deviation of the coupling may not be realistic, since the position of the lifting piston could have not been perfectly centered. This second stage has demonstrated however that the coupling accepts a wide range of pipe movements without leaks. Conclusions This first test has been conducted to draw a preliminary confirmation of the acceptance of pipe deflection inside the coupling under load / settlement. The results have been positive, therefore the test is considered fully satisfactory. As next step, a precise test procedure will be prepared and verified with Bureau Veritas. The test will then be repeated in presence of Bureau Veritas representative, who will certify the test. After that, conclusions in terms of coupling length, insertion length, configuration of the coupling s body, etc. will be reached. Preliminarily, the standard configuration of the coupling (ratio length to diameter, tolerance, etc.) are permitting axial deflections up to ±3 (6 total) with pipe under pressure and without leaks. Nova Siria compression coupling_test protocol - page 5 of 12

6 End coupling data sheet Nova Siria compression coupling_test protocol - page 6 of 12

7 Test coupling data sheet Nova Siria compression coupling_test protocol - page 7 of 12

8 (top) Test structure, general view. Note at left the hand pump for the pressurization. (bottom) test structure, lateral view. Right, one of the two terminals N50=1250, center the test coupling WSP10S The piston supporting the coupling are visible at the center of the structure. Nova Siria compression coupling_test protocol - page 8 of 12

9 (top) the test coupling at the star of the test (center) Left inclination after release of the bottom support shown on one of the two electronic inclinometer (bottom) Test manometer showing the test 6 bar pressure Nova Siria compression coupling_test protocol - page 9 of 12

10 (Top) position of the pipe at the end of the test. Inclination of the pipe are respectively of 2,8 and 3,1. The coupling has partially followed the pipe movement reaching an inclination on the vertical of 2,7. The black lines show the pipe movement inside the coupling. (Side) the end coupling have followed the inclination of the pipe. The pipe however has not moved from the original position Nova Siria compression coupling_test protocol - page 10 of 12

11 (top) Pipe and coupling position after re lifting the coupling. Inclinations are +1 (left), +0,4 (right) and 5,3 to right (coupling) (Bottom) the configuration seen from the opposite side Nova Siria compression coupling_test protocol - page 11 of 12

12 The conditions of the pipe surface after the deflection and counter deflection has been examined. No damage, scratch or sign has been found. Nova Siria compression coupling_test protocol - page 12 of 12