The following language is adapted from Statement G of the Plastics Pipe Institute adopted on October 1, 1974.

The PPFA believes that indented markings on plastic pressure pipes could in some cases adversely affect their service life. The effect will vary depending on the specific plastic pipe compound and the geometry of the marking. It is recommended that indented marking be used only after the specific pipe compound and the specific marking have been adequately evaluated, particularly by means of long-term hydrostatic strength tests. It is recommended that markings which do not rub off during normal handling and installation be used. The following statement is suggested for inclusion in codes:

All required markings shall be legible and so applied without indentation, as to remain legible under normal handling and installation practices. Pipe and tubing made from materials, such as polyolefins (polybutylene, polyethylene, polypropylene), which are difficult to mark satisfactorily without indenting may be so marked provided (1) the marking does not reduce the wall thickness to less than the minimum requirement for the pipe or tubing and (2a) it is demonstrated that these marks have no significant effect on the long-term hydrostatic strength of the pipe or tubing or (2b) the specification under which the pipe is purchased contains a Section similar in content to that of 7.3.1 in ASTM D2241-73 which reads as follows:

7.3.1 Test Specimens - Not less than 50 percent of the test specimens required for any pressure test shall have at least a part of the marking in their central sections. The central section is that portion of pipe which is at least one pipe diameter away from an end closure.

NOTE:
This PPFA User Bulletin is designed to provide guidance in achieving the efficient, effective and informed use of plastic pipe. The suggestions and advice contained in this Bulletin are offered merely to provide plastic pipe users with a general frame of reference. Because specific situations may, and often do require special treatment, the suggestions and advice are obviously not universally applicable. Therefore, the user should carefully assess the requirements of his specific situation before making practical application of anything contained in this publication.