BS ISO 10471:2018 pdf download – Glass-reinforced thermosetting plastics (GRP) pipes — Determination of the long-term ultimate bending strain and the long-term ultimate relative ring deflection under wet conditions
7 Number of test pieces
Unless otherwise specified in the referring standard, at least 18 test pieces shall be used to obtain the distribution of failure times specified in the referring standard (see the numbered list in Clause 4).
8 Determination of the dimensions of the test piece
8.1 Length Measure the length of each test piece along each reference line in accordance with ISO 3126. Trim or replace, as applicable, the test piece if it does not conform. Calculate the mean length, L, in metres, of each test piece from the six measured values.
8.2 Wall thickness Measure in accordance with ISO 3126 the wall thickness of each test piece at four equally spaced locations on each reference line. For each reference line, calculate the mean wall thickness, e, in metres, of the four measured values. Calculate the sample mean wall thickness using all thickness values.
8.3 Mean diameter Measure in accordance with ISO 3126 either the internal or external diameter (see 3.2). Using either Formula (1) or Formula (2), calculate the mean diameter, d m (see 3.2), of the test piece using the value obtained for the sample mean wall thickness, e, in 8.2.
9 Conditioning If applicable, condition the test pieces in accordance with the referring standard.
10 Procedure
10.1 For each test piece conduct the following procedure at the temperature specified in the referring standard (see Clause 4).
10.2 To assess the uniformity of the test pieces, determine and record in accordance with the constant load procedures in ISO 7685 the initial specific ring stiffness, S 0 , of each test piece. The measured value of S 0 at the pair of reference lines (see Clause 6) may also be used to estimate the force required to compress the test piece to the necessary deflection to achieve a time to failure that, together with those produced from other test pieces, conforms to the distribution of times to failure specified in the referring standard.
10.3 Deflections in excess of 28 % of the diameter may cause local flattening of the pipe and lead to erratic test results. For deflections approaching 28 %, improved accuracy is obtained by use of strain gauges to establish, for each pipe product, a calibration scale of deflection versus measured strain. This calibration technique is useful at all deflection levels. If such a calibration procedure is established then it shall be used to determine the strains for all test pieces in the test series.
10.4 Place a test piece in the apparatus in contact with the upper and lower plate or beam bar with the pair of diametrically opposed reference lines vertically aligned. However, if the applied force is expected to result in relative deflections that can be in excess of 28 %, use at least one beam bar. Ensure that the contact between the test piece and each bearing plate or beam bar is as uniform as possible and the plates and/or beam bars are not tilted laterally. Place the apparatus in the water container.
10.5 Fill the container with water so that the test piece is fully immersed.
10.6 When the test piece is fully immersed in the water and taking account, as necessary, of the weight of the upper plate or beam bar, and of any spacer, apply the vertical compressive force, F, so that the corresponding vertical deflection is reached within 3 min and record the actual force applied and deflection achieved.
10.7 While maintaining the force applied in 10.6, measure and record at predetermined intervals of time the elapsed time and the deflection of the test piece, using either suitable manual devices or automatic recording equipment. When failure (see 3.9) occurs, the time to failure, t u , and the deflection at failure, y u , wet, shall be taken as:
a) either the elapsed time and its associated deflection recorded on the automatic device (the preferred, recommended and most accurate method);
b) or the last recorded readings, prior to failure occurring, of deflection and its associated time.