In the past. International Standards specifying the tolerances to be applied to thermoplastics pipes have covered individual materials separately. The philosophy of ISO 11922 is to combine these already published standards into a single two-part standard covering the tolerances for extruded pipes manufactured from all thermoplastics materials, thus avoiding the need for a standard to be developed for each individual material.
ISO 11922 therefore contains a number of tolerance grades covering the mean outside diameter, the out-of-roundness of the outside diameter, the wall thickness at any point and the mean wall thickness. The bodies responsible for writing the various product and system standards will choose, from the specified tolerance grades, that grade which is suitable for the application and material involved.
