One of the major risks with horizontal directional drilling (HDD) is the striking of a utility line resulting in loss of life, property damage and social dislocation.
Historically, mechanical damage is the single largest cause of failures on pipelines.
Immediate failure typically occurs when construction equipment punctures the pipe and produces a leak at the time of damage.
Gas transmission pipelines from 300-1,000 mm diameter move large volumes of gas from gas fields to distribution networks. The pressure of gas in these lines typically ranges from 6 MPa (870 psi) to 16 MPa (2,320 psi). As a safety measure, pipelines are designed and constructed to handle much more pressure than is ever actually reached in the system. Pipelines in more populated areas operate at less than one-half of their design pressure level.
Pipelines are laid at depths of 1,200 mm (greater at crossings) in right-of-ways typically 25 m wide. Markers are installed to identify approximate pipeline location, but not pipeline depth.
Mitigation measures
Pipeline operators are increasingly demanding that risk assessments be made of drilling activity within the pipeline right-of-way to identify threats from drilling, and outline control measures to mitigate risks.
Mandatory measures have included:
- A directional drilling plan to be prepared, outlining all drilling parameters and reviewed by pipeline operator;
- Confirming DBYD pipeline locations by exposing pipelines using soft dig technology and further question those pipelines that might be missing;
- In order to ensure minimum clearance between pipeline and drilling installation inspection/spot holes to be installed either side of the pipeline to monitor the drill head travel;
- During the back reaming process, contractors should visually observe the back reamer passing an existing utility during pullback to ensure that potential reamer migration does not occur.
Never assume the location of pipelines. They can change directions abruptly and without any aboveground physical evidence (even between marker posts). Their depths vary, and more than one pipeline may exist within a right-of-way.