30-inch, Gas Pipeline Integrity Assessment

Location: Louisiana (US)

A midstream company required a Department of Transportation (DOT) integrity assessment on a 30-inch transmission gas pipeline. In order to meet federal compliance standards for continued gas operations, the operator elected to execute a hydrostatic pressure test between an existing compressor station and a mainline valve location. Several variables in the scope of work registered high in the preliminary risk assessment:

  • Heavy populated commercial and residential areas required official notification and time for relocation.
  • Heavy traffic railway corridors required official prior notice with no usage during pressure test schedule.

Specification

  • Diameter: 30 inches
  • Length: 16.5 miles
  • Wall Thickness: 0.375 inches
  • Maximum Allowable Operating Pressure (MAOP): 1,440 psi

Challenges

  • Engineered pig train calculations for chemical cleaning.
  • Engineered volumetric calculations for pipeline flooding.
  • 8-hour CFR standard hydrostatic pressure test; 30-minute CFR standard hydrostatic spike pressure test.
  • Pre-engineered pipeline calculations for de-watering procedure to prevent air lock on elevation profile changes.
  • Pipeline fluid water treatment as specified by state guidelines.
  • Drying to -40°F with ¼” penetration for product preparation.

Plan of Execution

  1. Pipeline Cleaning
    1. Chemical surfactants
    2. Defoaming agents
    3. Mechanical pigging systems
    4. AquaGel® Pig Systems
  2. Pipeline Flooding
    1. Utilization of filtered water from an adjacent natural source.
    2. 1.5 miles of 8-inch above ground piping for source water transportation.
  3. Hydrostatic Pressure Test
    1. 12-hour pressure stabilization period.
    2. 8-hour approved pressure test.
    3. 30-minute spike test at 139% of MAOP.
    4. Utilization of real-time electronic data recording instrumentation.
  4. Pipeline Dewatering
    1. Relinquish used test medium into natural surrounding  per state regulations.
    2. Mechanical pigging systems.
  5. Pipeline Air Drying
    1. Achieved dew point of -40°F and ¼ inch penetration.

Technical Achievements & Benefits

  • Successfully executed Management of Change (MOC) orders to accommodate clean pipe specifications.
  • Responsive field supervision provided real time solution for unplanned water source failures.
  • Executed 24-Hour SIMOPS schedule to overcome severe weather delays as a result of a tropical storm.
  • Test medium discharge satisfied state environmental regulations.
  • Jobs completed with zero incidents and no environmental impact.