LOUISVILLE, Ky. (WDRB) – The Adair County natural gas pipeline that ruptured earlier this year, triggering a massive explosion that leveled nearby homes, had “pre-existing” cracks in a weld where the pipe broke, an analysis found.

Those cracks and stresses on the pipeline – such as shifting soil – contributed to its failure in the early morning of Feb. 13 near Knifley, Ky., about 100 miles south of Louisville, according to the metallurgical report filed with federal regulators.

The report, obtained under the U.S. Freedom of Information Act, found no evidence that the cracks grew over time. Instead, a consultant for pipeline operator Columbia Gulf Transmission concluded they likely occurred as hydrogen lodged in the weld when the pipeline was installed in 1965.

Columbia Gulf did not answer questions about whether company officials had prior knowledge of the cracks.

The segment of the pipeline that failed – between Hartsville, Tenn., and Clementsville, Ky. – was inspected in 2004 and 2011, according to Columbia Gulf. The company declined to say if the 2011 inspection documented the cracks in the weld.

“We are currently addressing your questions with the Pipeline Hazardous Materials Safety Administration,” Columbia Pipeline Group spokesman Scott Castleman said in a statement. “As soon as these answers become public, we will be happy to share them with you.”

Columbia Gulf expects to submit a report with federal authorities around the end of the year, Castleman said.

Richard Kuprewicz, a Redmond, Wash., consultant who specializes in gas pipeline incident investigations, reviewed the analysis at the request of WDRB News. He wrote in an email that the general threat of hydrogen-related cracking in pipelines has been well-known for some time.

(In fact, the concerns that led Indiana to shut down and repair the Sherman Minton Bridge between Louisville and New Albany, Ind., in 2011 were connected to similar cracking in 1960s-era steel.)

Pipeline operators routinely use technology such as “smart pigs” that travel through pipelines looking for defects during inspections, but Kuprewicz said such cracks can still be hard to notice even with those tools.

In the mid-1960s, there were no federal limits on how much carbon pipelines could contain, according to the Det Norske Veritas report, which concluded the Columbia Gulf line's steel had carbon amounts above modern standards.

“The higher the carbon the more brittle the steel and susceptible to cracking problems,” Kuprewicz wrote. He said hydrogen-related cracking is “likely a threat that may exist on other segments of this pipeline that were constructed at the same time or nearly the same time.”

Columbia Gulf declined to address Kuprewicz's conclusion, but it did say it installed 285 miles of pipeline in Kentucky between 1960 and 1969.

“There are several technical issues with these older pipelines, whether they're being re-purposed or simply continuing to function as they were initially intended,” said Tom FitzGerald, director of the Kentucky Resources Council.

FitzGerald said those include ”age, the quality of the weld, the tendency of pipe over time to shift because of shifting in the ground. All of these things can be contributors to failures.”

The pipeline breach ignited a blast and fire that destroyed two homes and caused nearly $1.8 million in property damage. Regulators deemed it a “significant” event – one that kills or hospitalizes people, causes more than $50,000 in damages or results in fire or explosion.

The line that failed carries natural gas across central and eastern Kentucky. The February rupture was the second “significant” incident on the line within a two-year period.

There have been 175 “significant” pipeline incidents in the U.S. in 2014, including two in Kentucky, according to data compiled by the pipeline safety administration. In June, a “flash fire” occurred during welding of an Owensboro crude oil pipeline operated by Marathon Pipe Line, federal data shows. No injuries or damage were reported.

Columbia Gulf operates more than 3,400 miles of natural gas pipelines in the southeastern U.S., including roughly 1,390 miles in Kentucky. The company is affiliated with Houston-based Columbia Pipeline Group.

Following the Adair County rupture, the Pipeline Safety Trust of Bellingham, Wash., analyzed federal pipeline data for Columbia Gulf and found the company had more than twice as many “significant” incidents as the national average for such pipelines.

Columbia Gulf began placing the line near Knifley back in service last month, a company spokeswoman said.

“We have worked countless hours to examine what happened in Adair County and to ensure that we take every precaution to keep an incident such as this one from happening again,” Katie Dupuis Martin, a Columbia Pipeline Group spokeswoman, told WDRB News earlier this year.

Reporter Marcus Green can be reached at (502) 585-0825 or on Twitter @MarcusGreenWDRB.

Copyright 2014 WDRB News. All rights reserved.