Page 238 - Trenchless Technology Piping Installation and Inspection

202 Cha pte r F i v e

operation. The inspector should ensure that bends are not drilled at a
radius of curvature less than the recommended minimum. If an
apparently overly small radius occurs, the unacceptable portion of
the borehole should be redrilled. If redrilling is not practical or proves
unsuccessful, the problematic section should be reviewed with the
design engineers to consider the possibility the pipe can function
properly and that the codes and specifications governing design of
the pipeline are not violated.
The actual position of the drilled path usually cannot be visually
confirmed. Therefore, it is necessary for the inspector to have a basic
understanding of the downhole survey system being used by the con-
tractor and be able to interpret its readings. It is not necessary for the
inspector to continuously observe and approve the drilling operation.
However, progress should be monitored periodically and problems
addressed so that remedial action can be taken as soon as possible.
Drilling Fluids
The inspector should document all drilling fluid products being used,
the contractor’s pumping pressures and rates, and details relative to
drilling fluid circulation at the endpoints of the HDD installation. The
right-of-way and surrounding areas should be examined regularly for
inadvertent returns. If inadvertent returns occur, they should be
contained or cleaned up in accordance with the specifications and
permits, and their locations monitored for continuing problems. See
the “Disposal of Excess Drilling Fluids” section in Sec. 5.3.4 for addi-
tional information.

Additional Concerns
Depending upon the contractual and technical aspects of an HDD
installation, there are numerous additional details which should be
reviewed and documented. These may consist of gauge readings, pro-
duction rates, equipment failure, downtime, etc. During pullback, it is
important to record the contractor’s operations relative to handling of
the pipeline. Anti-buoyancy control measures, if used, should also be
recorded. Following the completion of pullback, the condition of any
visible pipe and coating at the leading edge of the pull section should be
documented. The final steps in accepting project delivery may include:
• Preservation of entry and exit stakes until the pilot borehole
is completed.
• Staking and verification of the distance, alignment, and ele-
vation between the final as-built and initially designed entry
and exit points.
• Maintenance of the following survey information for gener-
ating certified (“as-built”) documentation:
• Tabular data
• Preparer’s assumptions