HDPE Solid and Corrugated Pipes
Hydrostatic Strength of NEXOR HDPE Pipes Test Procedure
June 6, 2006
The procedural standard of hydrostatic HDPE pipe test performed at NEXOR PIPES is detailed below.
Hydrostatic pipe test measures the resistance of pipes to internal pressure. It is one of the easiest ways to assess long term performance if piping materials. The methodology performed at NEXOR PIPES, which closely follows ISO 1167, is detailed below.
Preparation of Test Pieces
Three test pieces are required. The length of the pipe between the end caps must be at least the length listed on table 1.
Table 1 Length of Test Pipe
A pipe after being extruded must be allowed to sit for a minimum period of 24 hours before performing a hydrostatic test. A conditioning period must also be followed to ensure that the pipe walls achieve thermal equilibrium. Conditioning is done by placing the pipe inside the test bath at the specified test temperature for a period indicated on table 2.
Table 2 Conditioning Period
Calculation of Test Pressure
The test pressure is calculated based on the design stress of the pipe material and using the following formula.
P = 10σ(2)/(SDR-1) ..1
P = test pressure in bar
σ = is the stress to be induced by the applied pressure, in MPa.
SDR = standard dimension ratio of the pipe
The design stress is based on the Minimum Required Strength (MRS) at 50 years and 20 0C and the design coefficient.
PE 80 has an MRS of 8 MPa and the minimum design coefficient is 1.25; both of these lead to a maximum design stress of 6.3 MPa.
Using a design stress of 6.3 MPa and formula 1, table 3 lists some of the test pressures at various SDRs.
Table 3 Sample test pressures for PE 80 with a Design Stress of 6.3 MPa
Application of Test Pressure
Pressure is applied in a steady incremental manner at the rate of 30 psi per minute.
Measuring Hydrostatic Strength according to ISO
Following ISO 4427 and ISO 1167, the three test pieces are to be subjected to different test conditions. Each are listed on table 4 for PE100 and PE 80.
Table 4 Three different Test Conditions - Test Stress, Temperature, and Time
Based on the test stresses, the following test pressures are to be applied for a given SDR. The values given in tables 5 to 8 have a tolerance of +/- 1 psi.
Table 5 Test Pressures for SDR 9
Table 6 Test Pressures for SDR 11
Table 7 Test Pressures for SDR 13.6
Table 8 Test Pressures for SDR 17
In case of pipe failure, the mode of failure is recorded and a picture of the pipe is taken.
A failure is brittle if there is no visible yield deformation.
If a break occurs ain the test piece at a distance of less than 10 % of the length of the test piece from the end cap, the results must be disregarded.
Please see attached sample report.
ISO 1167 -1 Thermoplastics pipes, fittings, and assemblies for the conveyance of fluids Determination of the resistance to internal pressure. Part 1 : General Method.
ISO 1167 -2 Thermoplastics pipes, fittings, and assemblies for the conveyance of fluids Determination of the resistance to internal pressure. Part 2 : Preparation of Pipe Test Pieces.
ISO 4427 Polyethylene Pipes for water supply - Specifications
Chasis, David. Plastic Piping Systems. 2nd Ed. Industrial Press Inc. USA. 1988
Willoughby, David et al. Plastic Piping Handbook. Mcgraw-Hill Handbooks. USA. 2002