Longitudinal Reversion of NEXOR HDPE Pipes – Test Procedure

NEXOR Pipes R&D

July 8, 2006

ABSTRACT

The procedural standard of longitudinal reversion test for HDPE pipe performed at NEXOR PIPES.

Introduction

Residual stresses inherent in the extrusion of plastic pipe products may have long term adverse effects on product performance. In particular, ESCR or environment stress cracking is accelerated in pipes with high frozen in internal stresses. Longitudinal Reversion Test is a method of determining the level of internal stresses in pipes. Below describes the longitudinal reversion test procedure performed at NEXOR PIPES ; the methodology closely follows ISO 2505 Thermoplastic Pipes – Longitudinal Reversion – Test Method and Parameters.

Principle

A pipe of specified length is placed in an air oven at a specified temperature for a specified time. A marked length of this portion of pipe is measure before and after heating. The reversion is calculated as a percentage of the change in length in relation to the initial length. (ISO 2505:2005)

Procedure

Preparation of Test Pieces

Test may only be performed on pipes 24 hours after production.

Prepare three samples each with a length of 200+/-20mm long. Two circumferential marks are traced 100mm apart at equal distances from two ends.

Air Oven

Air oven must be set to 110+/2 Celsius.

At room temperature, (23 degrees Celsius +/- 2) measure the distance of the two circumferential marks using a caliper.

Then, suspend the test piece in the air oven (110 C). The test piece may only be placed in the air oven if the oven has reached the set temperature.

In placing the test sample in the air oven, the actual temperature of the oven must return to the set temperature within 15 minutes.

The duration of exposure is as follows:

60 minutes for pipes with wall thicknesses equal and below 8mm.

120 minutes for pipes with wall thickness above 8mm

Measure the separation between the circumferential marks when the samples have returned to room temperature.

Calculation of Results

Longitudinal Reversion is calculated as follows

R­­­_­­_{L,  =}  ∆L/L_o x 100

Where,

∆L =  L_o –L;

∆L may be positive or negative.

L_o is the distance between the marks before the exposure in mm

L is the distance between the marks after the exposure in mm.

Calculate the value of the longitudinal reversion R­­­_­­_L of the three sample pieces. Report the arithmetic mean of the three values.  

Test Reporting

Please see attached sample report.

References

ISO 2505:2005 Thermoplastic Pipes – Longitudinal Reversion – Test Method and Parameters

ISO 4427 Polyethylene Pipes for water supply - Specifications

Chasis, David. Plastic Piping Systems. 2^nd Ed. Industrial Press Inc. USA. 1988

Willoughby, David et al. Plastic Piping Handbook. Mcgraw-Hill Handbooks. USA. 2002