Pressure Testing, Commissioning, and Restoration
Hydrostatic testing
A strength test verifies the line at a pressure above MAOP - commonly 1.25 times MAOP for new steel transmission lines, subject to the class location, the applicable regulation (49 CFR Part 192 or Part 195), and the project specification. The test sequence is fill, remove air, pressurize in stages, stabilize, hold for the specified duration, and inspect for leaks. Hold time does not begin until pressure and temperature have stabilized; temperature changes can mask or simulate a leak, so the test must be evaluated with temperature-compensated data. Gauges and recorders must be calibrated and within their valid range.
Records, water, and disposal
Know the test records - chart or digital data, gauge certifications, test section limits, elevations, and calculation of the test pressure. Test water source, quality, and discharge require approval and permitting; dewatering and disposal follow the plan.
Commissioning and restoration
Commissioning includes drying, purging (with inert gas where required), gas-up or fill, odorization, valve and SCADA checks, and turnover documentation. Restoration covers topsoil replacement, revegetation, erosion and sedimentation controls, removal of temporary facilities, cleanup of spills and waste, and landowner walk-through.
Traps
Watch for questions that start hold time at first reaching pressure, ignore elevation differences within the test section, or skip leak inspection because the pressure held. Also expect traps around pneumatic testing safety and unauthorized water discharge.
Worked example
Rule of thumb: for a 1,440 psi MAOP gas transmission line, a 1.25× strength test is 1,800 psi. The clock starts only after pressure and temperature stabilize, and the section must be walked and inspected at test pressure.