MEXICO — A stress corrosion crack caused the massive natural gas explosion March 3 north of Mexico, according to an incident report.

The report, filed by Energy Transfer Partners with the Pipeline and Hazardous Materials Safety Administration, was released April 2. Energy Transfer is the owner of the Panhandle Eastern Pipeline, which ruptured approximately one mile north of Mexico near Missouri Highway 15. The company had 30 days to submit a report to the safety administration.

The 30-inch diameter pipe is comprised of carbon steel, with a specified minimum yield strength of 60,000 pounds per square inch. Pressure inside the pipe did not exceed the maximum allowable operating pressure. The investigation did not find evidence of human error or control room malfunctions.

The widest part of the rupture was 94 inches and the entire rupture’s circumference was 864 inches in a pipe buried five feet underground. Two people were evacuated from the incident area, but no injuries or fatalities were reported.

Approximately $1.14 million of property damage occurred within the 621-foot potential impact radius. Highway 15 was cooked by the fire, approximately 50 to 75 yards away. A house under construction by Matt and Shawna Penn was destroyed. Total incident cost — property damage and the estimated cost of the released gas — is $1.4 million.

The last time the pipeline received an internal inspection at the incident point was in 2015 with a tool propelled down a pipe to study the internal shape and if there were any dents or pipe wall changes. They also performed a test to detect steel corrosion or pitting by magnetizing the pipe and looking for deformations in the magnetic field, which indicate integrity problems. These tests were also performed in 2008, according to the report.

Energy Transfer conducted multiple hydrotests on a 15-mile stretch of the pipeline in the weeks since the incident. After four failed tests, a successful test was conducted last Monday. Before the explosion, hydrotesting had not been conducted on the line since its installation in 1962. Direct assessments that would require unearthing the pipeline also were not conducted by Energy Transfer since the installation.

It is estimated that 91,719 cubic feet of natural gas was released during the incident, which is slightly more than would fit into a standard Olympic swimming pool. This includes unintentional release and intentional blowdown of gas as valves to the line were closed.

An approximately 16-mile section of pipe was isolated and shut down between valve gates due to the rupture. The pipe used a supervisory control and data acquisition system, which was in operation and fully functional at the time of the incident and helped assist in the detection and confirmation of the rupture, according to the report. However, the rupture was initially identified by local operators.

Four employees received drug and alcohol testing following the incident, per regulations. All tests came back negative for drugs and alcohol.

cdunlap@gatehousemedia.com