Hydrostatic Strength of HDPE Pipes – Test Procedure NEXOR Pipes June 6, 2006 ABSTRACT The procedural standard of hydrostatic HDPE pipe test performed at NEXOR PIPES is detailed below. Introduction
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. Procedure 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
PIPE OD (mm)
Length of Test Piece from end cap to end cap(mm)
20
250
25
250
32
250
40
250
50
250
63
250
75
250
90
270
110
330
125
375
140
420
160
480
180
540
200
600
225
675
250
750
280
840
315
945
355
710
400
800
450
900
500
1000
560
1120
630
1260
710
1420
800
1600
900
1800
1000
2000
Conditioning 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 Thickness (mm)
Conditioning Period (h)
<3
1
>3 and <8
3
>8 and <16
6
>16 and <32
10
>32
16
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 SDR
Test Pressure (psi)
9
228 +/- 1
11
183 +/- 1
13.6
145 +/- 1
17
114 +/- 1
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 Pipe Material
Test Stress (MPa) of Condition 1 (100 h, 0 20 C)
Test Stress (MPa) of Condition 2 (165 h, 0 80 C)
Test Stress (MPa) of Condition 3 (1000 h, 0 80 C)
PE 100
12.4
5.5
5.0
PE 80
9.0
4.6
4.0
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 Pipe Material
Test Pressure (psi) of Condition 1 (100 h, 0 20 C)
Test Pressure (psi) of Condition 2 (165 h, 0 80 C)
Test Stress (psi) of Condition 3 (1000 h, 0 80 C)
PE 100
450
199
181
PE 80
326
167
145
Table 6 Test Pressures for SDR 11 Pipe Material
Test Pressure (psi) of Condition 1 (100 h, 0 20 C)
Test Pressure (psi) of Condition 2 (165 h, 0 80 C)
Test Stress (psi) of Condition 3 (1000 h, 0 80 C)
PE 100
360
159
145
PE 80
261
133
116
Table 7 Test Pressures for SDR 13.6 Pipe Material
Test Pressure (psi) of Condition 1 (100 h, 0 20 C)
Test Pressure (psi) of Condition 2 (165 h, 0 80 C)
Test Stress (psi) of Condition 3 (1000 h, 0 80 C)
PE 100
285
126
115
PE 80
207
105
92
Table 8 Test Pressures for SDR 17 Pipe Material
Test Pressure (psi) of Condition 1 (100 h, 0 20 C)
Test Pressure (psi) of Condition 2 (165 h, 0 80 C)
Test Stress (psi) of Condition 3 (1000 h, 0 80 C)
PE 100
225
99
90
PE 80
163
83
72
Pipe Failure 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. Test Reporting Please see attached sample report. References 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 nd
Chasis, David. Plastic Piping Systems. 2 Ed. Industrial Press Inc. USA. 1988 Willoughby, David et al. Plastic Piping Handbook. Mcgraw-Hill Handbooks. USA. 2002
