This International Standard specifies a method for determining by extrapolation the long-term ultimate bending strain and the calculation of the long-term ultimate relative ring deflection of glass-reinforced thermosetting plastics (GRP) pipes, under wet conditions. Two methods of loading are given, one using plates the other beam bars. NOTE Either method may be used for measurements of relative vertical deflection up to 28 %. When it is expected that this level is going to be exceeded then the procedure is limited to the use of at least one beam bar.