While there were no fatalities and injuries, the incident resulted in the evacuation of 16 businesses and 51 residences and the destruction of the building. In the end, property damages were $875,000, according to a report just released by the National Transportation Safety Board (NTSB).
Upon further review, the lead up to the explosion was fairly quick as at 9:26 a.m. the day of the incident, a member of the public called 911 and reported smelling gas about a quarter mile north of Steffens Auto Parts.
At 10:26 a.m., responders from ONE Gas, Inc.’s Kansas Gas Service Division arrived onsite. ONE Gas crews conducted continuous monitoring for gas accumulation, initiated leak investigations to identify migration pathways, and ventilated affected infrastructure, including buildings, vaults, and sewer systems.
Leak identification efforts ended up complicated by severe winter weather conditions, which hindered excavation and leak detection. The region experienced prolonged freezing temperatures during the week preceding the accident, with snow and ice cover.
Diagnosing Gas Main
The 10-inch diameter main involved in this accident was a loop line that supplied gas to multiple regulator stations serving much of Hutchinson’s gas distribution system north of the Arkansas River.
This configuration necessitated employing an isolation plan focused on safely securing the leak location while minimizing service disruptions. At 3:15 p.m., ONE Gas crews began isolating the affected pipeline segment by closing selected valves. The final valve required for complete isolation closed at 3:34 p.m. Firefighters fully extinguished the blaze at 8:51 p.m., according to the report.
The day following the accident, a ONE Gas crewmember excavated the main in the vicinity of the failure and identified the source of the leak on a 10-inch diameter gas main at 2:57 a.m. The main originally went in the ground in 1936 and crossed over an 8-inch diameter, 1908 vintage water main near the failure point, according to the report.
Steffens Auto Parts commercial building after the natural gas leak and explosion.
Source: Hutchinson Fire Department.
ONE Gas observed a separated girth weld at the top of the pipe. As excavation progressed around the weld location, the weld continued to separate until the main appeared completely severed, according to the report.
NTSB Materials Laboratory examination of the damaged pipe found the fractured girth weld was consistent with a low ductility overstress fracture. The weld, completed prior to the establishment of American Petroleum Institute (API) 1104 welding standards and federal pipeline safety regulations, exhibited lack of penetration and a lack of fusion in multiple locations along he fracture surface.
Type of Weld
Metallurgical examination confirmed the weld characteristics were consistent with a manual oxy-acetylene torch weld performed by rolling the pipe during fabrication prior to installation in the ditch.
Pipeline and Hazardous Materials Safety Administration regulations require pipeline operators to prepare and implement a Distribution Integrity Management Program (DIMP) that evaluates risks associated with their distribution pipelines, including identifying applicable threats, estimating likelihood of failures, and assessing potential consequences.
ONE Gas DIMP included “accelerated actions,” or measures designed to reduce the likelihood and consequences of known threats.
Industry guidance identified oxy-acetylene welds as known threats when subjected to external forces such as those resulting from heavy rains, floods, and earth movements.
ONE Gas used a probabilistic risk model to identify the likelihood and consequences of failure for any threat identified in the development of their DIMP.
ONE Gas used this risk model to identify assets for replacement and risk mitigation projects. Before the failure, ONE Gas determined the threat associated with oxy-acetylene welds were stable and not an actionable threat within its system. ONE Gas had no prior failures associated with oxy-acetylene welds before this incident.
Ten-inch diameter gas main girth weld crossing over the 8-inch vintage water main.
Source: Baker Risk
As a result of its investigation, NTSB determined the probable cause of the explosion was the failure of a ONE Gas 1936-vintage 10-inch-diameter natural gas main at an oxy-acetylene girth weld that exhibited lack of penetration and fusion from original construction that decreased the strength of the weld; the weld failed when undetermined external forces induced an overstress fracture, allowing natural gas to migrate underground and accumulate within a commercial building, where it ignited.
Lessons Learned
Vintage oxy-acetylene welds remain at increased risk of failure under external forces, such as ones that produce earth movement, according to pipeline industry guidance. In this incident, a vintage oxy-acetylene weld failed without any indication of external forces.
Careful monitoring of all external loading conditions can help identify areas where oxy-acetylene welds may have an increased risk of failure.
Following the accident, ONE Gas implemented several safety actions designed to improve future safety performance. To better evaluate system integrity for all possible external forces, ONE Gas enhanced data collection practices, including review of utility crossings near vintage welds, to reduce the risk of damage to pipe welds. Additionally, ONE Gas developed a new field material failure report allowing failure data reporting in real time, improving data quality and timeliness for integrity management analysis.
Click here to read the full report.