CSB Ties Failure to Inspect to NDK Blast
NDK Crystal, Inc. for years did not conduct inspections of the pressure vessels used to generate large crystals, under very high pressure and temperatures, at its Belvidere, Ill., plant, according to the investigative agency.
Stress corrosion cracking in the 8-inch-thick steel wall of a pressure vessel caused its catastrophic failure on Dec. 7, 2009, at the NDK Crystals, Inc. plant in Belvidere, Ill. The vessel was 120 days into a 150-day crystal manufacturing cycle when it ruptured. NDK did not inspect any of the plant's eight pressure vessels, and the cracking in this one went undetected for years, the U.S. Chemical Safety and Hazard Investigation Board determined, as illustrated in a newly posted "Falling Through the Cracks" video about the explosion.
The blast hurled projectiles more than 200 yards, killing a motorist at a nearby filling station and injuring someone in a nearby building when a piece of debris crashed through a wall.
A consultant hired by NDK's insurer investigated an earlier accident, when hot, caustic material leaked from another vessel's lid, found that stress corrosion cracking had caused it and strongly recommended that the pressure vessels not be returned to service, but NDK did not follow that recommendation. No certified inspector ever performed an internal inspection of the failed vessel during the six years it was in use, according to CSB's new video.
The video was released simultaneously with the CSB investigation report on the accident that the board considered Nov. 14 at a public meeting in Rockford, Ill. "The video dramatically describes the important findings of the CSB investigation – pressure vessels did not meet code requirements, but were granted an exemption; internal corrosion inspections were recommended but never performed; and finally a specific warning was made to the company by its insurer. But at every level, the risk of catastrophic vessel failure was overlooked and public safety, literally and figuratively, fell through the cracks," CSB Chairperson Rafael Moure-Eraso said.
"The video shows how cracking on and near the inner diameter of the vessel fragment reduced the vessel material toughness, which eventually led to large flaws resulting in the catastrophic failure," added CSB Lead Investigator Johnnie Banks.