This document describes requirements, design and installation of flexible pipe elements (e. g. metallic flexible pipe, metallic flexible tube, vibration isolator, expansion joint) and non-metallic tube used in the refrigerant circuits of refrigerating systems and heat pumps. It also describes the requirements to qualify the tightness of non-metallic tubes (e.g. plastic) used in evaporating and/or condensing sides of refrigerating systems and heat pumps. It does not apply to flexible pipes that are only occasionally stressed beyond the elastic limit, e. g. during repair work, or to joints which are free to rotate or hinge.