Abstract ISO 23228:2011 proposed a testing method in which the plastic material, experimental resins or compounds for pipes and fittings, can be exposed to stress conditions that mimic internally pressurised end‐capped pipes. The stress conditions are mimicked by the use of a plaque specimen having a grooved reduced section called plane–strain grooved tensile (PSGT) specimens producing a biaxial state of stress under uniaxial loading. In this study, PSGT specimens were cut out from high‐density polyethylene (HDPE) pipes. Two shape ratios, ratio between the width and the groove thickness, were used. Both the axial and transverse displacements and strain fields were followed by a digital image correlation (DIC) camera during tensile and creep loading, both at room and high temperature; furthermore, DIC images were used to estimate the notch opening displacement. The increasing effect of the temperature in both the axial and transverse displacement and strain was highlighted. No significant effect of the width was noticed. The results have evidenced that, as the plane–strain condition in the width is assured during the tests, PSGT specimens can be used to mimic internally pressurised pipes under monotonic increasing or constant‐in‐time loading at both room and high temperature, but it must be better to use specimens with a higher shape ratio, that is, higher width. The results contribute to the 9th Sustainable Development Goal: Industry, Innovation and Infrastructure by promoting a sustainable industrialisation and fostering innovation.