Page 149 - Pipeline Rules of Thumb Handbook

136 Pipeline Rules of Thumb Handbook

Figure 5. Test thermometer placement. Courtesy Milbar Hydrotest.

The pumps used to fill the line should have sufficient capac- accept the leakage test if there is no pressure drop in a three
1
ity to fill the line at a rate of about / 2 mile per hour. Water hour period.
filters should be used and are normally equipped with one A pressure-volume plot may be required, especially if the
hundred mesh screens. See Figure 4 for a typical fill site test pressures approach or exceed the SMYS of the pipe.
arrangement. Some companies may specify a finer mesh The plot is made manually during the pressuring operation
screen. The filling unit should be equipped with a flow meter by recording pump strokes on the X-axis and pressure on
to measure the amount of water pumped into the pipeline. the Y-axis. A straight line will be produced until the plastic
Temperature recorders will be used to record ambient tem- range of the pipe is reached or until a leak occurs. This type
perature, the temperature of the pipe and water, and ground of plot is also useful should a joint of lighter wall thickness
temperature. See Figure 5 for typical test thermometer place- or lower yield strength pipe be inadvertently placed in the
ment. A pressure recorder will be used to provide a record- pipeline.
ing of the pipeline test pressure. A deadweight tester will be Small leaks during the testing operation can be difficult to
used to calibrate the pressure recorder. A high pressure pump locate. A change in the water/pipe temperature may give
capable of delivering 70 to 150gpm at a pressure exceeding the appearance of a leak. If the temperature of the pipe/
the required test pressure will be used in the final pressuring water decreases, the test pressure will decrease. An increase
operation. Small high pressure units with a capacity of 6 to in water/pipe temperature will cause the test pressure to
30gpm may be used for short sections of large diameter lines increase. The effect of a temperature change may be esti-
and smaller diameter lines. mated using the equations and data contained in Appendixes
Deadweight pressure and temperature readings are re- A and B. To achieve any degree of accuracy in these calcula-
corded after the prescribed test pressure has been reached tions, it will be necessary to have accurate temperature and
and the pressures and temperatures have stabilized. A pres- pressure readings.
sure vs. time plot may also be made. Readings are usually The pipeline test temperature may be affected by river/
made at fifteen minute intervals for the first hour and at thirty creek crossings along the pipeline route. Also, if cold
minute intervals thereafter. The procedure for accepting a river water is used, there will be a changing temperature
leakage test will vary from company to company. Some will gradient. Air, either trapped or entrained, will also affect the