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NDK Crystal Inc. Explosion with Offsite Fatality

Overview

A violent rupture of a 50-foot pressure vessel used to produce synthetic crystals at the NDK Crystal facility in Belvidere, Illinois launched projectiles offsite. One public fatality, one public injury, and significant property damage occurred at NDK Crystal and an adjacent business.

Incident Snapshot

Field Value
Facility / Company NDK Crystal, Inc.
Location Belvidere, IL
Incident Date 12/07/2009
Investigation Status CSB investigation report approved by a 3-0 vote at a public meeting on November 14, 2013, in Rockford, IL.
Accident Type High-Pressure Vessel Rupture; Community Impact Investigation
Final Report Release Date 11/14/2013

What Happened

  • On December 7, 2009, at approximately 2:30 pm, State Special Vessel No. 2, under an operating pressure of 29,000 psig, suddenly and violently ruptured, 120 days into a 150-day operating cycle.
  • A white cloud of steam and debris rapidly expanded outward from the facility, traveled onto the interstate, and dissipated within seconds.
  • The sudden release of superheated liquid caused an eight-foot tall by four-foot wide vessel fragment, weighing approximately 8,600 pounds, to travel through two concrete walls and finally land about 435 feet from the NDK building.
  • The fragment skipped across a neighboring facility parking lot and struck the wall of an adjacent business office.
  • The thrust from the escaping liquid caused the base of the vessel to shear away from its foundation and blew pieces of structural steel out of the building into the parking lot of a nearby rest stop gas station, known as the Illinois Tollway (I-90) Oasis.
  • One piece of structural steel struck and killed a truck driver at the rest stop.
  • The Belvidere Fire Department arrived on scene at 2:41 pm.
  • The Chief of the Belvidere Fire Department assumed the role of incident commander.
  • Lifeline Helicopter airlifted the member of the public who was struck by the 100-pound steel beam to the hospital.
  • He was pronounced dead at 3:15 pm that day.
  • NDK immediately shut down all operations at the facility.
  • On January 29, 2010, the Illinois State Fire Marshal’s Office suspended operational certifications for all eight vessels at NDK.

Facility and Process Context

  • The NDK Crystal facility in Belvidere, Illinois is a synthetic quartz manufacturing facility that was built in 2002 and began operation in 2003.
  • The facility is located in a light industrial area adjacent to Interstate 90.
  • The NDK Belvidere facility is five stories tall and houses eight vertical pressure vessels called autoclaves.
  • The vessels are 50 feet tall and made of over eight-inch thick steel.
  • NDK Crystal shares the property with NDK America, Inc., the sales and marketing portion of the company.
  • The Belvidere facility is the only NDK production facility in the United States.
  • The process used raw mined quartz, or lasca, and a caustic sodium hydroxide solution in hydrothermal crystal growing operations.
  • The vessels were used to produce synthetic crystals under high temperature and high pressure conditions.
  • The vessel interior included an acmite coating intended to protect the inner walls from corrosion by the caustic sodium hydroxide.

Consequences

  • One public fatality.
  • One public injury.
  • An employee at Grupo Antolin received minor injuries.
  • Six NDK Crystal employees were present in the production area at the time of the explosion, but were uninjured.
  • Environmental sampling found dust accumulations consisted of building construction materials disturbed during the explosion.
  • Testing was insufficient to determine whether silica from the lasca was released.
  • Soil surface pH was slightly influenced, but the consultant concluded the released materials would not cause adverse environmental or health exposure risks.
  • The NDK production facility sustained major damage.
  • Exterior insulating panels were completely blown off.
  • The force of the explosion and the displaced vessel destroyed steel framing, stairwells, and floor grating near Vessel No. 2.
  • The office and lab areas showed varying degrees of damage and much of the final product was destroyed.
  • The product storage area, laboratory, and production offices were heavily damaged.
  • The NDK America facility attached to the NDK Crystals production facility also received major damage.
  • The neighboring facility, Grupo Antolin, received damage to one wall, multiple ceiling tiles, and lights from the impact of the 8,600-pound projectile.
  • Several automobiles in the parking lot sustained damage from the force of the explosion and flying debris.
  • NDK immediately shut down all operations at the facility.
  • The Illinois State Fire Marshal’s Office suspended operational certifications for all eight vessels at NDK.
  • As of the publication date of the case study, the NDK Crystal facility remained shut down.

Key Findings

Immediate Causes

  • Stress corrosion cracking likely caused the catastrophic rupture of a high-pressure crystal production vessel at NDK Crystal, Inc.
  • The fracture initiated at an existing, surface-breaking crack in the inner diameter of the lower portion of the vessel near the base.
  • Internal stress corrosion cracking was identified as the failure mechanism.

Contributing Factors

  • The caustic liquid created a degrading environment inside the vessel, particularly in small surface scratches, and likely resulted in the development of stress corrosion cracking.
  • The evidence of stress corrosion cracking in the fragment suggests that the acmite did not adequately protect the vessel, or that it was removed from this region of the vessel through mechanical processes such as scratching or abrasion during product removal or vessel cleaning between runs.
  • Temper embrittlement is another mechanism of failure that may have contributed to the formation of the critical crack, or accelerated the stress corrosion cracking.
  • The vessels exceeded the ASME wall thickness recommendations for closed-end forgings, which may have resulted in improper heat treatment during the manufacturing process.
  • The NDK vessel maximum thickness at the top and bottom was more than double the "typical value" listed in the code.
  • The design package for the NDK vessels did not mention the impact of the caustic service fluid on the interior of the vessel, and the designer did not specify appropriate materials or other considerations, such as the acmite coating, for corrosion prevention.
  • NDK relied on the acmite coating to act as an impervious barrier between the caustic environment and the inner surface of the vessel.
  • NDK did not perform regular inspections of the vessel interior to ensure the acmite coating was providing adequate corrosion protection.
  • After the 2007 lid failure, NDK did not further examine the origin of the stress corrosion cracking issues on the lid material prior to putting the vessels back into service.
  • NDK did not perform annual internal inspections as recommended by the vessel designer when the vessels were initially constructed.
  • The vessel was located in an enclosed building.
  • The rupture generated several projectiles.
  • The Code sections did not include specific limitations of material thickness for the design of heavy pressure vessels made with carbon and low-alloy steels.
  • The material listing used for the NDK vessels had no required thickness limit.
  • The caustic sodium hydroxide solution used inside the NDK pressure vessels was known to be corrosive to carbon steel.
  • The vessels received their initial certification from the state of Illinois for noncorrosive service.
  • The state only required the vessels' exteriors to be inspected along with their safety relief valves.
  • No internal inspections were performed.
  • Improper material selection was identified.
  • Excessive wall thickness contributed to the vessel failure mechanism, stress corrosion cracking.
  • The lack of a regular vessel inspection program by the company and state fire marshal allowed the conditions resulting in the vessel rupture to go undetected.
  • Investigation findings from a previous incident involving vessel lids did not prompt the company to take proper actions to ensure vessels were safe for operation.
  • NDK relied on the acmite layer to protect the inner walls from corrosion by the caustic sodium hydroxide.
  • NDK did not verify the integrity or the effectiveness of this coating, and the caustic chemicals promoted stress corrosion cracking that weakened the vessel.
  • Temper embrittlement, or some other form of heat treatment embrittlement, cannot be ruled out as a contributing factor in addition to the stress corrosion cracking.
  • The vessels exceeded the ASME wall thickness recommendations for closed end forging, which may have resulted in improper heat treatment during the manufacturing process.

Organizational and Systemic Factors

  • NDK continued to operate the seven remaining vessels with intact lids, without performing thorough inspections of the vessel bodies by a certified professional.
  • NDK’s approach to safety was informal, lacking formalized job training, standard operating procedures, and an incident and injury notification and investigation program.
  • NDK did not have a scheduled inspection program for the entire length of the vessel interior.
  • Despite warnings and the recommendation to inspect all vessels, NDK continued operation while focusing on the redesign of the lids without examining the origin of the stress corrosion cracking identified by the consultant.
  • The state said it relied on the company to perform internal inspections, but it did not verify whether these were actually occurring.
  • The Board reviewed ASME Boiler and Pressure Vessel Code, Section II, Part A, and Section VIII, Division 3, Alternate Rules for Construction of High Pressure Vessels (2001 edition).
  • ASME added a requirement to the forgings section (KM-211.2) for ASME Section VIII, Division 3 vessels to ensure large heat treated vessels receive mechanical tests to prove that the material has received proper heat treatment in the areas of highest stress in the vessel where cracking could occur.
  • ASME declined to make the requested changes to material and thickness requirements because the NDK vessel that exploded and prompted this recommendation could not be certified to the existing ASME Code SA-723 steel requirements.
  • The current thickness requirements are informational only as noted by the word “typical” and, thus, are not requirements.
  • The vessels received their initial certification from the state of Illinois for noncorrosive service.
  • The state only required the vessels' exteriors to be inspected along with their safety relief valves.
  • The Illinois Board of Boiler and Pressure Vessel Safety did not conduct internal inspections of the NDK vessels as required under state regulations for pressure vessels subject to internal corrosion.
  • The State Inspector only inspected accessible external surfaces and pressure relief devices.
  • The designer from EPSI recommended annual internal inspections such as magnetic particle and ultrasonic examinations to ensure corrosion was not occurring inside the vessels.
  • NDK did not perform such inspections and there was no oversight from the Illinois Chief Inspector to ensure NDK was inspecting the vessels as recommended.
  • Specific warnings were made to the company by its insurer admonishing the company of the danger to the public from a pressure vessel rupture.
  • In 2007, a consultant to the insurance company said that the vessels were unsafe.
  • The insurance company disavowed covering any damage or injuries resulting from operating these vessels.
  • NDK had no regular inspection program for the interior of the vessels.
  • No certified inspectors ever entered vessel number two throughout its service life.
  • NDK was planning on replacing the vessel, but had not done so by the December 2009 incident.
  • The company believed this acmite coating would protect the vessels from the corrosive effects of the chemicals inside.
  • The state did not conduct internal inspections, nor did they have a process to ensure NDK was performing the recommended internal inspections on the three vessels that did not meet the ASME code required properties.
  • The city of Belvidere did not identify NDK as a risk to public safety in 2001.
  • No off-site consequence analysis was conducted.
  • The documentation NDK submitted to the city did not include details of the pressure vessel process.
  • The safety program was somewhat informal, lacking formalized job training, standard operating procedures, and an injury and incident notification and investigation program.

Failed Safeguards or Barrier Breakdowns

  • The rupture disk on the lid of vessel 2 did not activate, indicating there was no excessive pressure build-up in the vessel prior to rupture.
  • NDK has no documentation of any internal inspections of Vessel No. 2 throughout its six-year service life.
  • Other than regular visual inspections of the top portion of the vessel between runs, NDK did not have a scheduled inspection program for the entire length of the vessel interior.
  • NDK contracted a metallurgical consultant to perform an ultrasonic inspection only on the top portion of Vessel No. 1 and found no internal discontinuities.
  • NDK performed weld repairs on the cracks near the pressure sensor connections on the vessel closure heads.
  • The ASME code strictly prohibits welding for SA-723 forged steel.
  • The Illinois Board of Boiler and Pressure Vessel Safety did not conduct internal inspections of the NDK vessels as required under state regulations for pressure vessels subject to internal corrosion.
  • The State Inspector only inspected accessible external surfaces and pressure relief devices.
  • The designer from EPSI recommended annual internal inspections such as magnetic particle and ultrasonic examinations to ensure corrosion was not occurring inside the vessels.
  • NDK did not perform such inspections and there was no oversight from the Illinois Chief Inspector to ensure NDK was inspecting the vessels as recommended.
  • Internal corrosion inspections that were recommended were never performed on the vessel that ruptured, or any of the other vessels.
  • The pressure vessels did not meet code requirements that were granted an exemption to function.
  • The vessel's rupture discs did not activate.
  • NDK did not perform recommended non-destructive examinations of all the vessels prior to returning the vessels to service.
  • NDK did not perform annual internal inspections as recommended by the vessel designer when the vessels were initially constructed.
  • The state did not conduct internal inspections.
  • The state conducted vessel inspections in 2003, 2006, and 2009, and inspected only external and accessible surfaces of the vessels.
  • The city of Belvidere did not identify NDK as a risk to public safety in 2001.
  • No off-site consequence analysis was conducted.
  • The company continued to operate these vessels without performing recommended inspections.

Recommendations

  1. 2010-4-I-IL R1 — Recipient: AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) — Status: Closed – Acceptable Alternative Action — Summary: Revise the ASME Boiler and Pressure Vessel Code to include specific material thickness limitations for the design of pressure-containing components to ensure proper heat treatment and avoid environmentally induced damage mechanisms. Clarify required vessel wall thickness limitations for SA-723 steel in the following code sections: a) ASME BPVC Section II, Part A, Material Requirements b) ASME BPVC Section VIII, Division III, Article KM-400, Material Design Data
  2. 2010-04-I-IL-R1 — Recipient: American Society of Mechanical Engineers (ASME) — Status: Closed – Acceptable Alternative Action — Summary: Revise the ASME Boiler and Pressure Vessel Code to include specific material thickness limitations for the design of pressure-containing components to ensure proper heat treatment and avoid environmentally induced damage mechanisms. Clarify required vessel wall thickness limitations for SA-723 steel in ASME BPVC Section II, Part A, Material Requirements and ASME BPVC Section VIII, Division III, Article KM-400, Material Design Data.
  3. 2010-04-I-IL-R3 — Recipient: Office of the Illinois State Fire Marshall (IL-OSFM) — Status: Closed – Acceptable Action — Summary: Prohibit the use of the existing pressure vessels at the NDK facility for crystal growing operations.
  4. 2010-04-I-IL-R4 — Recipient: Office of the Illinois State Fire Marshal (IL-OSFM), Boiler & Pressure Vessel Safety Division — Status: Closed – Acceptable Action — Summary: Develop and implement state requirements and procedures to ensure the pressure vessel approval process accurately identifies vessels that may be subject to corrosion or similar deterioration mechanisms, and ensure regular inspections in accordance with these state requirements.
  5. 2010-04-I-IL-R5 — Recipient: NDK America, Inc. formerly NDK Crystal, Inc. (NDK) — Status: Closed No Longer Applicable — Summary: For the design and operation of any new NDK Crystal facility using a hydrothermal or equivalent crystal growing process, ensure that the facility uses a process that is rigorously demonstrated to be inherently safer than the existing process (for example through using lower temperatures and pressures, and/or less corrosive conditions).
  6. 2010-04-I-IL-R6 — Recipient: NDK America, Inc. formerly NDK Crystal, Inc. (NDK) — Status: Closed No Longer Applicable — Summary: Implement a program to ensure the ongoing integrity of any coating used on the new process vessels. Employ an expert (e.g., a coatings expert certified by NACE International (National Association of Corrosion Engineers)) to design the program.
  7. 2010-04-I-IL-R7 — Recipient: NDK America, Inc. formerly NDK Crystal, Inc. (NDK) — Status: Closed No Longer Applicable — Summary: Implement an annual inspection and corrective action program to ensure vessels remain resistant to environmentally induced damage mechanisms based on the inspection guidelines set forth in the American Petroleum Institute (API) Standard 510, Pressure Vessel Inspection Code.
  8. 2010-04-I-IL-R8 — Recipient: NDK America, Inc. formerly NDK Crystal, Inc. (NDK) — Status: Closed No Longer Applicable — Summary: Commission a facility siting study of the NDK Crystal facility by an independent consultant. Identify all vessel failure scenarios prior to restarting the crystal growing process. The siting study should include the consequences, necessary preventive measures, and emergency planning and response programs relevant to each failure scenario for all surrounding points of concern. Provide a copy of this study to the City of Belvidere Building and Zoning Department and the Illinois Boiler and Pressure Vessel Safety Division.

Key Engineering Lessons

  • Pressure vessel design for caustic service must account for environmentally induced damage mechanisms, including stress corrosion cracking.
  • Material thickness and heat treatment requirements for heavy pressure-containing components must be explicit and enforceable, not merely informational.
  • Protective coatings cannot be assumed effective without a program to verify their integrity over time.
  • Internal inspection programs are necessary when vessels are subject to internal corrosion or similar deterioration mechanisms; external-only inspections are insufficient.
  • Prior cracking or lid failures should trigger investigation of the underlying failure mechanism before returning vessels to service.
  • Facility siting and off-site consequence analysis are necessary when vessel failure can project hazardous debris beyond the site boundary.

Source Notes

  • Priority 1 final report used to resolve conflicts and establish authoritative findings, consequences, and recommendations.
  • Priority 3 recommendation status documents were used to update recommendation statuses and confirm follow-up actions.
  • Priority 4 transcript was used only to supplement event sequence, facility context, and consequences where consistent with higher-priority sources.
  • Terminology such as "stress corrosion cracking", "acmite coating", "State Special Vessel No. 2", and "Closed – Acceptable Action" was preserved from the source documents.

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