ISO 13967:1998 PDF

This International Standard specifies a method of determining the ring stiffness of bends and branches made from thermoplastic material and for use with plastics pipes having a circular cross-section.

The method can be used to determine the stiffness of bends, equal branches and unequal branches, provided that the fitting allows a ring deflection of at least 4 %.

If a fitting has the same wall thickness, wall construction, material and diameter as a pipe being tested, then, because of its geometry, its stiffness will be equal to or greater than that of the pipe tested. In this case, the fitting can be classified as having the same stiffness class as the pipe, without testing.

Any unequal branch may be expected to have at least the same stiffness as an equal branch, provided that it has the same main diameter, wall construction and material as the equal branch.