OP,
Not too much about it is stated in the Code ( Assume B31.8). Table 4.9 in CSA Z662 specifies a clearance of 300 mm for underground cables and pipeline.
However, you need to be careful about when the pipeline is close to the grounding facilities of electrical transmission line structures, substation, generating stations and other facilities that has high fault current carrying grounding network. Fault current can damage to personnel and pipieline coating and steel.
Where buried pipelines are close to high fault current-carrying grounding networks, remedial measures can be necessary to protect the pipeline from resulting potential gradients in the earth near the pipelines.
GDD
Canada