Introduction
When you test by the given method, approximately 300mm length of pipe shall not alter in length by more than 5%.
Test Sample
- After extrude the pipe you must keep the pipe at 23±2 °C for at least 2 hours.
- Then you can get a 300±20mm length of sample from above pipe.
- Then you must trace (mark) two circumferential marks apart 100mm (L0) on the test specimen (One of the marks must be at least 10mm from one end of the sample).
- Repeat above trace three times at the same sample as given image.
- After that, drill or cut two holes at least 15mm from other end of sample to insert Metal Wire ( Two holes must be on diameter and parallel to mouth of pipe).
Preparing Apparatus
The apparatus shall consist of Thermostatically Controlled bath at 150±2°C. And it shall be made for effective agitation to ensure that the temperature tolerance is maintained throughout the heating medium. You can use Glycerine, Glycol, Silicone Oil, Vaseline Oil ( Free from aromatic hydrocarbons ) or a solution of calcium chloride.
When you choose the heat transfer medium, it must be stable at the temperatures required and it does not affect the sample.
Procedure
- First of all you must measure the two marks to within 0.2mm ( Using vernier Caliper ) at 23±2 °C.
- Then control the temperature of the heating medium at 150±2 °C.
- Then suspend the test piece vertically using inserted metal wire in the heating medium by the end furthest from the marks, so that immersed portion of the test piece is at least 20mm long.
- Make sure the sample is not touch wall or base of the bath.
- After that leave the test piece immersed for,
15min
for pipes of maximum specified thickness equal to less than 8mm.
30min
for pipes of maximum specified thickness more than 8mm.
- After that remove the test piece from the bath and suspend them vertically.
- Then allow them to cool by exposure to the air at 23±2 °C.
- After complete cooling, get four measures of the distance between the marks at 23±2 °C within 0.2mm.
Test Results
For each distance between two marks, calculate the Longitudinal reversion as a percentage by following the formula.
Lo is the distance between the marks in millimeters before test
.
L is the distance between the marks in millimeters after the test.
Choose the measurement of
L which gives the greatest value of
|ΔL| where
ΔL could be positive or negative.
