Scratch Depth Tolerance
When pulling a plastic pipe into the path created by the bursting unit, it is possible that pipe fragments resulting from the original pipe may impose some scratches or gouges on the outer pipe surface. In general, such effects have not been problematic, based on a long history of successful installations. However, precautions may be necessary when upsizing greater than one size, particularly for the replacement of ductile iron pipe. It is also required that visible surface scratches be less than 10% of the wall thickness, based on inspection of the leading end of the pipe at the exit pit. Additional details are provided in Chapter 16 of the Plastic Pipe Institute (PPI) Handbook of Polyethylene Pipe.