Post-Construction DCVG Surveys on Three New Crude Oil Pipelines Near Jal and Carlsbad, New Mexico (2020)

A new pipeline is never in better shape than on the day it is backfilled. That is why the project specifications for three crude oil lines in southeast New Mexico required a DCVG survey before closeout. We ran those surveys in spring 2020 for the contractor that built them.

Surveying a line with no CP yet

None of the three lines had a cathodic protection system yet, only monitoring test stations. So at each connection point we installed a portable rectifier and temporary anodes and adjusted the current until the instant off potential at the connection was at least -1.1 V against copper sulfate. Then we walked the line with a field data logger and two copper sulfate electrodes, recording the voltage gradient every 5 to 7.5 feet. A peak of 5 mV or more marks a possible holiday, and each one is confirmed by setting the electrodes in four quadrants around it and checking that the current points toward the same spot. The reports also note two limits of any aboveground survey: it may miss a defect hidden under a poorly applied girth weld wrap, and it loses sensitivity below about 10 to 15 feet of cover, which matters on bores.

Two lines without a defect

The 8-inch lateral near Carlsbad, about 7,600 feet long, was surveyed on April 6, 2020 and showed no indications at all. Less than 20 mA was enough to bring the whole line to full protection, with very little signal loss, which says the coating went in nearly perfect. The 12-inch first phase near Jal, about 14.75 miles, was surveyed from April 6 to 9 with the current applied at two test stations, 24 mA and 11 mA, and it was also free of indications.

Five defects on the longest line

The second phase of the 12-inch line in Lea County, about 27.5 miles, was surveyed from June 12 to 17, 2020. It took more current, up to 360 mA at some connection points, and the survey found five coating defects: one small, two medium and two large. One sat near a valve site riser, and another near a test station where a third-party line crosses. Given their apparent size, we said excavation and repair may be warranted, and we strongly recommended a cathodic protection system and a maintenance program for the line.

Related services

The method is described in more detail on our page for DCVG surveys.