All dents that affect the curvature of the pipe at the longitudinal weld or any cicumferential weld shall be removed.
All dents that exceed a maximum depth of 1/4" in pipe NPS 12 shall not be permitted in pipelines or mains intended to operate at hoop stress levels of 40% or more of the specified minimum yield strength.
When dents are removed, the damaged portion of the pipe shall be cut out as a cylinder.
Insert patching and pounding out of the dents is prohibited.
How you manage a dent in a pipeline can vary temendously based on the actual dent and the location and/or service of the pipeline. Your regulatory regime may also dictate what you have to do.
You should consider a fitness for service approach and there are methodologies available though the PDAM (Pipeline Damage Assessment Manual Group), Pipelien Research Council International (PRCI) and many other published works such as kiefner et al.