CSB s NDK Crystal Case Study 1

NDK Crystal Case Study Final Investigation Report November 2013

Case Study

U.S. Chemical Safety and Hazard Investigation Board

NDK Crystal, Inc., Belvidere, IL

High-Pressure Vessel Rupture 

December 7, 2009

One Public Fatality, One Public Injury

No. 2010-04-I-IL

This case study examines the violent rupture of a 50-foot pressure vessel used to produce synthetic crystals at the NDK 

Crystal facility in Belvidere, Illinois. The vessel, located in an enclosed building, generated several projectiles during the 

explosion that resulted in one fatality and one injury to members of the public, and significant property damage to NDK 

Crystal and to an adjacent business. 

KEY ISSUES

s 0RESSURE 6ESSEL $ESIGN AND

-ATERIAL 3ELECTION 2EQUIREMENTS

s ,EARNING FROM 0REVIOUS )NCIDENTS

s )NSPECTIONS

INSIDE

s )NTRODUCTION

s 0ROCESS $ISCUSSION

s )NCIDENT $ESCRIPTION

s #ONSEQUENCES

s -ETALLURGICAL !NALYSIS

s &INDINGS

s 2ECOMMENDATIONS
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NDK Crystal Case Study Final Investigation Report November 2013

1.0 INTRODUCTION

1.1 NIHON DEMPA KOGYO (NDK) CO., LTD.

Founded in 1948 in Tokyo, Japan, Nihon Dempa Kogyo CO., 

LTD. (NDK) began producing synthetic crystal products and 

over time, has expanded its production and sales facilities to the 

United States, Europe and Asia. NDK produces and sells crystalrelated products such as oscillators, ultrasonic transducers, and 

synthetic quartz. These products are commonly used in cell 

phones and wireless internet devices. 

1.2 FACILITY DESCRIPTION

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 autoclaves1

 (cover photo). 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 (Figure 1). The Belvidere 

facility is the only NDK production facility in the United States.

TABLE OF CONTENTS

 )NTRODUCTION 

 0ROCESS $ISCUSSION 

 )NCIDENT $ESCRIPTION 5

 !NALYSIS 

 2EGULATORY !NALYSIS 

 +EY &INDINGS 

 2ECOMMENDATIONS 

 !PPENDIX ! 20

 !PPENDIX " 21

1 An autoclave is a heavy, heated vessel assembly commonly used for sterilization or conducting chemical reactions under high pressure and temperature.

&)'52% 

/VERHEAD VIEW OF .$+

FACILITIES 'RUPO !NTOLIN

NEIGHBORING COMPANY	

AND )
 4OLLWAY AND

/ASIS REST AREA
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NDK Crystal Case Study Final Investigation Report November 2013

1.2.1 Vessel Description

The eight NDK vessels were designed and built for crystal growing operations that require a 

vessel material and thickness to withstand high operating pressures. The vessels consist of a 

48-foot long cylindrical shell and a 2-foot thick closure head that operators clamp to the top. 

The cylindrical wall is 8.1 inches thick and the top and bottom of the vessels are significantly 

thicker than the vessel walls at 18-1⁄4 inches near the lid and 16-1⁄4 inches at the base (Figure 3). 

Engineered Pressure Systems, Inc. (EPSI) designed and engineered the vessels and Sheffield 

Forgemasters (Sheffield), a large steel casting and forging supplier in the U.K., forged2

 the 

vessels in 2002 and 2003. Sheffield constructed the vessels from alloy steel to meet the 

material specifications of the American Society of Mechanical Engineers (ASME) Boiler and 

Pressure Vessel Code SA-723 Grade 2 steel3

 (Appendix A). The 140,000-pound vessels have 

a maximum allowable working pressure (MAWP) of about 30,000 pounds per square inch 

gauge (psig) and maximum operating temperature of 750°F. Operators replaced the pressure 

relief device after each crystal growing cycle because of the high operating pressure. Each 

vessel had about three crystal-growing cycles per year.

1.2.1.1 Illinois State Special Vessels

After fabrication, Sheffield could not certify that the first three manufactured vessels were 

compliant with the ASME Boiler and Pressure Vessel Code (BPVC) because the vessel material 

did not meet the required mechanical properties for that class of steel. NDK petitioned the 

Illinois Boiler and Pressure Vessel Safety Division to grant special authorization to use the 

vessels. At a meeting held by the division in June 2002, technical representatives for NDK 

claimed that although the Charpy4

 tests did not meet all the ASME Code requirements at 

lower temperatures, they showed acceptable material toughness at the operating temperature 

of 700°F. As an alternative to meeting code requirements, Sheffield asserted that the vessel 

material toughness was adequate and that the material passed the Charpy test at 212°F. The 

State had an independent party review the vessel design package. In September 2003, the State 

of Illinois gave NDK approval to use vessels 1, 2 and 3 and classified them as “state special” 

pressure vessels. Sheffield manufactured vessels 4 through 8 from a material with different 

mechanical properties that passed the Charpy impact test at 70°F.5

 The manufacturer applied 

the ASME BPVC Section VIII, Division 3 Code stamp to those vessels. 

2.0 PROCESS DISCUSSION

2.1 PROCESS DESCRIPTION

The NDK quartz-manufacturing vessel simulated natural 

geologic crystal growth through heat and high pressure, 

known as hydrothermal synthesis. The process began 

with raw mined quartz, or lasca (Figure 2), lowered in 

baskets into the bottom of the vessel using an overhead 

crane. Operators then added 800 gallons of four percent 

sodium hydroxide and water solution, and a small amount 

of lithium nitrate into the vessels. Next, operators hung 

&)'52% 

! BASKET OF MINED QUARTZ

LASCA	 PRIOR TO A CRYSTAL


GROWING RUN

2 Forging is the shaping of metal between dies by mechanical or hydraulic pressure.

3 American Society of Mechanical Engineers (ASME) 2001, Specification for Alloy Steel Forgings for High-Strength Pressure Component Application, 

SA-723/SA-723M-2001. ASME Boiler and Pressure Vessel Code Section II Part A, ASME New York, NY.

4 The Charpy test is an impact test that measures the amount of energy a material can absorb.

5

 Sheffield constructed vessels 1, 2 and 3 from alloy steel (SA-723 Class 3 Grade 2). Vessels 4 through 8 were forged from SA-723 Class 3 Grade 3 steel.
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NDK Crystal Case Study Final Investigation Report November 2013

“seed crystals” at the top of the vessel. 

The seed crystals are wafer-thin pure 

quartz crystals with the desired grain 

structure on which the new crystals 

grow. Operators sealed the vessel with 

10,000-pound lids clamped to the 

top. External electric heaters slowly 

increased vessel temperature to 700°F, 

which boiled the caustic liquid and 

increased the pressure inside the vessel 

to about 29,000 psig (Figure 3). 

The natural quartz crystal, or lasca, 

dissolved in the liquid solution. Natural 

circulation caused the supersaturated 

solutions to rise to the top of the 

vessel, where the temperature was a 

few degrees lower. High purity quartz 

crystals grew on the seed crystals over 

a period of 100 to 150 days and formed 

a high-purity synthetic quartz product. 

When the vessel run was completed 

and returned to ambient temperature, 

operators removed the finished quartz 

product and the racks from the vessel. 

NDK laboratory technicians examined 

the crystals for quality control 

purposes and shipped the product to 

the NDK facility in Japan for further 

processing (Figure 4). 

Operators then cleaned the empty vessel 

interior with a pressure washer and 

vacuumed the water out of the vessel. All 

excess caustic and water solution was 

transferred to a holding tank where it was 

treated and neutralized prior to disposal.

In addition to NDK, there is one other 

crystal manufacturer in the U.S., located 

in Eastlake, Ohio. This company, in 

operation for 50 years, uses a sodium 

carbonate process and operates 

smaller, thinner-walled vessels at lower 

temperature and pressure than the 

sodium hydroxide process operated by 

NDK in Belvidere.6

&)'52% 

.$+ !UTOCLAVE #ROSS

3ECTION NOT TO SCALE	

&)'52% 

3YNTHETIC QUARTZ

PRODUCT

6

 The sodium carbonate process uses 0.6 to 0.8M sodium carbonate solution. The vessels are heated to 650°F and operate at a pressure of 10,000 

to 14,500 psi.
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NDK Crystal Case Study Final Investigation Report November 2013

2.2 ACMITE COATING

The caustic sodium hydroxide solution and silica reacted with the iron in the steel vessel 

wall and formed a coating known as acmite.7

 The presence of acmite, or sodium iron 

silicate, is significant in the manfufacturing of synthetic quartz and its use has been well 

documented in lower-strength steels as early as 1954.8

 Acmite serves a dual purpose for 

crystal manufacturing: to protect the surface of the vessel from corrosion and to avoid 

iron contamination in the final product. When NDK first received the vessels from the 

manufacturer, operators performed a “coating run” to apply a protective boundary between 

the liquid and the wall of the steel vessel.9

During the vessel operation, the acmite coating formed rapidly on the inner surface and 

coated the vessel wall. Because this high-strength, alloy steel vessel material was susceptable 

to corrosion, NDK relied on the acmite layer to prevent the alkaline process environment 

from corroding and weakening the vessel wall. 

3.0 INCIDENT DESCRIPTION

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 (Figure 5).

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 (Figure 6). The fragment skipped across 

a neighboring facility parking lot and slammed into the wall of an adjacent business office 

(Figure 7). The force of the impact pushed the wall inward causing furniture to shift and 

ceiling tiles to fall. One person working near the wall was injured.

&)'52% 

/ASIS SECURITY CAMERA

SHOWS THE EXPANDING

STEAM CLOUD AND DEBRIS

IMMEDIATELY AFTER THE

VESSEL RUPTURED

7 Acmite, also known as aegirine, is a greenish-grey rock-forming mineral that is stable at high pressures and temperatures.

8 Walker, A.C., Ballman, A.A., “Synthesis of Quartz Crystal.” Bell Telephone Laboratories, 1954.

9

 During the coating run, operators added lasca, seed crystal, the caustic solution, and a small amount of lithium nitrate to the vessel and heated 

the vessel to 650°F and 17,000 psig for 2 to 3 weeks.
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NDK Crystal Case Study Final Investigation Report November 2013

The thrust from the escaping liquid caused the base of the vessel to violently 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. After 

shearing from its base and throwing shrapnel out of the facility, the vessel swung from 

the building and landed on the ground outside (Figure 8).

&)'52% 

.$+ #RYSTAL DAMAGE

AFTER THE INCIDENT 6ESSEL

.O  RESTS ON GROUND

OUTSIDE STRUCTURE 4HE

FORCE OF THE EXPLOSION

BLEW OUT MOST OF THE

EXTERIOR WALL PANELS

&)'52%  ,%&4	

4HE  POUND VESSEL

FRAGMENT EXITED THE

.$+ PRODUCTION BUILDING

THROUGH A REINFORCED

CONCRETE WALL

&)'52%  2)'(4	

$AMAGE FROM VESSEL

FRAGMENT IMPACT

WITH ROADWAY
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NDK Crystal Case Study Final Investigation Report November 2013

3.1 CONSEQUENCES

3.1.1 Fatality and Injury

At the time of the incident, a member of the 

public was leaving the I-90 Tollway Oasis and 

returning to his truck when he was struck by 

a flying fragment propelled by the force of the 

vessel explosion. The seven-foot, 100-pound 

steel beam (Figure 9) from the NDK facility 

traveled about 650 feet, and struck and killed 

the truck driver. An employee at Grupo Antolin, 

an adjacent automotive supply company, 

received minor injuries because of the impact 

from the 8,600-pound vessel fragment against 

the exterior wall of the office area. Emergency 

medical services evaluated and treated the Grupo 

Antolin employee on-scene. Six NDK Crystal 

employees were present in the production area 

at the time of the explosion, but were uninjured. 

3.1.2 Property Damage

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 from the vessel 

rupture. NDK America employees relocated office activities for three months during repairs.

The neighboring facility, Grupo Antolin, received damage to one wall, multiple ceiling tiles, 

and lights from the impact of the 8,600-pound projectile from the pressure vessel (Figure 10). 

Several automobiles in the parking lot sustained damage from the force of the explosion and 

flying debris. One piece of shrapnel, a 2-foot by 2-foot window, landed in the Oasis parking 

lot, 950 feet away (Figure 11). 

&)'52% 

'RUPO !NTOLIN FACILITY

DAMAGE FROM

VESSEL FRAGMENT

&)'52% 

/VERHEAD PHOTO OF

EXPLOSION FRAGMENT

LOCATIONS AND DISTANCE

FROM THE FACILITY

&)'52% 

3TRUCTURAL STEEL FRAGMENT
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NDK Crystal Case Study Final Investigation Report November 2013

3.2 EMERGENCY RESPONSE

The Belvidere Fire Department arrived on scene at 2:41 pm. The Chief of the Belvidere 

Fire Department assumed the role of incident commander. Employees evacuated the 

buildings and NDK management and the fire department accounted for all personnel. 

Fire department personnel escorted employees and bystanders involved in the explosion 

to the northwest parking lot of the Grupo Antolin facility, where the Belvidere Fire 

Department and Lifeline Ambulance set up triage. Responders also checked the immediate 

area using a thermal imaging camera and found the 8,600-pound portion of a vessel 

registering a temperature of 325°F. There was no sustained fire or smoke near the location 

of the explosion. 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.

The CSB learned of the incident through media reports and notification from the National 

Response Center. Because of the public fatality, the CSB deployed a team of three investigators 

who arrived on scene two days later. The CSB entered an evidence preservation agreement 

with OSHA, EPA and NDK Crystal, interviewed employees, photo-documented the site, 

and preserved physical evidence for further examination. NDK immediately shutdown all 

operations at the facility and on January 29, 2010, the Illinois State Fire Marshal’s Office 

suspended operational certifications for all eight vessels at NDK.10

As of the publication date of this case study, the NDK Crystal facility remains shutdown. 

The seven remaining vessels are intact and contractors have performed significant demolition 

work to the surrounding superstructure. 

4.0 ANALYSIS

4.1 MECHANISMS OF FAILURE

CSB investigators reviewed process data for the vessel over the 120 days prior to the incident 

and found no evidence of a process deviation that might have caused the vessel to fail.11 As 

a result, the CSB entered into a joint metallurgical examination and testing agreement with 

OSHA, NDK, the insurance company, and other interested parties, to determine what caused 

the vessel to fail and whether the failure was caused by characteristics of the crystal-growing 

process or a problem with the vessel originating from its design and fabrication.

CSB investigators observed non-destructive evaluations (NDEs)12 and destructive testing 

performed on the 8,600-pound vessel fragment (Figures 12, 13). After consultation with 

engineers and metallurgists from the various agencies, the metallurgical lab cut several 

samples from the vessel fragment inner diameter, outer diameter, thickness, and fracture 

surfaces for microscopic examination and testing. The metallurgical labs involved in 

the vessel fragment examinations provided all participating agencies with test data and 

photographs collected during testing. The CSB commissioned an independent review of 

the data by expert metallurgists at the National Institute of Standards and Technology 

(NIST) Materials Reliability Division, to assist in identifying the failure mechanism. 

10 The vessel certifications remain suspended as of the publication date of this case study.

11 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. 

Vessel 2 pressure and temperature readings remained constant until the vessel ruptured.

12 Non-destructive testing (NDT) is a wide group of surface and volumetric examination techniques used to evaluate the properties of a material, 

without causing damage. Common NDT methods include ultrasonic, magnetic-particle, liquid penetrant, radiographic, and visual inspection.
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NDK Crystal Case Study Final Investigation Report November 2013

4.1.1 Stress-Corrosion Cracking

After a review of the metallurgical testing data, the CSB found strong evidence of cracking 

on and near the inner diameter of the vessel fragment. The cracks reduced the vessel 

material toughness,13 which eventually led to large flaws resulting in the catastrophic 

failure. Stress corrosion cracking (SCC) was the likely failure mechanism that caused the 

cracks. SCC is the formation of cracks through the simultaneous action of applied stresses 

and a corrosive environment.14 Microscopic examinations of the steel revealed strong 

evidence that SCC existed in many regions of the vessel fragment (Figure 14). The vessel 

at NDK contained an alkaline, or basic, sodium hydroxide and water solution generally 

known to damage some steels. The caustic liquid created a degrading environment inside 

the vessel, particularly in small surface scratches, and likely resulted in the development 

of SCC. The fracture initiated at an existing, surface-breaking crack in the inner diameter 

of the lower portion of the vessel near the base.

EPSI designed the vessels using the 

material NDK selected under the 

implied assumption that the acmite layer 

formation would prevent SCC in the 

vessel wall. The evidence of SCC in the 

fragment suggests that the acmite did 

not adequately protect the vessel, or that 

it was removed from this region of the 

vessel though some type of mechanical 

process, such as scratching or abrasion, 

during product removal or vessel cleaning 

between runs. 

During the fragment testing, metallurgists performed energy dispersive spectroscopy16 (EDS) 

to characterize the coating on the vessel inner surface. Test results reported the presence of 

silicon, titanium, and aluminum in significant quantities, and sulfur and chloride in smaller 

quantities. These are known impurities for the lasca used as a feedstock for crystal growth. 

This evidence suggests that the process fluid was able to penetrate the surface cracks in the 

vessel, indicating the acmite coating was not adequate.

&)'52% 

-ICROGRAPH OF CRACKING

FOUND ON THE FRACTURE

SURFACE ABOUT 

INCHES FROM INNER

DIAMETER SURFACE

OF VESSEL FRAGMENT

!CCORDING TO .)34 THE

BRANCHING OF THE CRACK

IS A TELLTALE SIGN OF 3##15 

&)'52%  ,%&4	


POUND VESSEL

FRAGMENT SUBJECTED TO

METALLURGICAL TESTS

&)'52%  2)'(4	

0HOTO OF THE RUPTURED

6ESSEL .O  WITH

INSULATION REMOVED

13 Toughness is the ability of a metal to resist fracture by absorbing the energy of applied stresses.

14 NACE International (2010). Stress Corrosion Cracking, NACE Resource Center. Retrieved from: http://events.nace.org/library/corrosion/Forms/scc.asp.

15 National Institute of Standards and Technology (NIST) Materials Reliability Division. (2013). Data Review and Report on Failure Mechanisms of NDK 

Pressure Vessel. Boulder, CO: Fekete, J. R., Sowards, J. W. & Amaro, R.

16 EDS is an analytical technique characterizes chemical elements on a sample surface.
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NDK Crystal Case Study Final Investigation Report November 2013

4.1.2 Temper Embrittlement

Temper embrittlement is another mechanism of failure that may have contributed to the 

formation of the critical crack, or accelerated the SCC. Temper embrittlement is a phenomenon 

inherently present in heat-treated steels. Heat treatment is a process to alter the hardness and 

ductility throughout a material’s microstructure. The control of time and temperature are 

critical to ensure a material has optimum mechanical properties for its intended use. Tempering 

is a heat treatment technique to decrease the steel hardness and increase ductility (decreasing 

brittleness), allowing the material to absorb more energy prior to failure. 

4.1.2.1 Charpy Tests

Metallurgists found possible evidence of temper embrittlement in the vessel sample from 

a review of Charpy impact test data. The Charpy impact test, also known as the Charpy 

V-notch test, is a standardized test, which determines the amount of energy absorbed 

by a material during fracture. A hammer on a pendulum arm strikes the sample specimen 

opposite the pre-machined notch. The energy absorbed by the specimen is determined by 

measuring the decrease in motion of the pendulum arm. This absorbed energy is a measure 

of a given material’s notch toughness and along with the appearance of the fracture surface 

can determine the minimum service temperature of a material.

The CSB made comparisons between the manufacturing certification and post-failure 

testing, and found there were considerable variations in toughness in different regions 

of the vessel. This general loss of toughness was identified in all orientations (not just 

circumferential), which, according to NIST, suggests a general damage mechanism, 

such as temper embrittlement was acting in addition to the SCC (Figure 14). The reduction 

in Charpy energy shows that the vessel’s ability to absorb energy before failure diminished 

over time, possibly caused by the SCC.

4!",%  6%33%, ./  #(!209 %.%2'9 $%#2%!3% 0/34 &!),52%

#OMPARISON OF #HARPY

IMPACT TEST RESULTS AFTER

MANUFACTURE AND POST

FAILURE -ANUFACTURERS

#HARPY DATA WERE

TAKEN FROM A DIFFERENT

ORIENTATION 0OST FAILURE

DATA POINTS ARE THE

AVERAGE OF THREE TESTS

IN FOUR ORIENTATIONS !LL

TESTS MEASURED AT a&
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NDK Crystal Case Study Final Investigation Report November 2013

4.1.3 Forging Process and Heat Treatment

The vessels at the NDK Crystal facility were all forged from a solid bar into a long cylinder, 

leaving the base of the vessel with an elliptical or “dished” end inside (Figure 3). The vessel 

lids came from the same ingot.17 The vessel was partially machined into shape, forged, heattreated, and quenched. Quenching with water puts the steel in a harder or more brittle state, 

and then it is tempered back to reduce hardness and increase ductility. 

The ASME Boiler and Pressure Vessel Code for this particular alloy steel18 has a 7-inch thickness 

limitation for quenching a closed-end vessel (Section 4.3.1.1). The NDK vessel maximum 

thickness at the top and bottom was more than double the “typical value” listed in the code. 

To determine if heat treatment issues contributed to the vessel failure, NIST reviewed the grain 

structure throughout the entire thickness of the vessel fragment. NIST concluded variations 

in grain structure through the vessel thickness were typical and there was no evidence that the 

vessel thickness resulted in inadequate heat treatment of the portion examined. The review of 

vessel fragment micrographs revealed expected microstructures for this type of steel. 

Though NIST could not find evidence of inadequate heat treatment in the vessel fragment, it 

is possible that a reduction in toughness could have existed in the thicker regions of the vessel. 

Because of the thickness of the vessel at the top and bottom, Sheffield performed a double water 

quench in attempt to achieve the desired toughness in the center regions of the vessel wall. 

Early in the fabrication process, two vessels did not cool evenly during the quench process and 

cracked near the bottom. As a result, Sheffield discarded the vessels and requested NDK change 

the material specifications on the vessels yet to be forged, to Class 3 Grade 3 steel, with a 

higher nickel content to meet the toughness properties required by the ASME code. 

4.2 NDK

4.2.1 Previous Incident

In January 2007, the closure head in Vessel No. 6 experienced an uncontrolled leak of 

the 400°F caustic sodium hydroxide solution that expelled through the threaded pressure 

sensor connection at the top of the vessel while in service. Hot, caustic material sprayed 

on the ceiling and fifth floor of the NDK Crystal facility. No one was injured as a result 

of the incident. NDK ceased production and initiated an investigation and examination 

of the vessel lids. A consultant hired by NDK conducted non-destructive examinations on 

the vessel lids and found very small cracks in four of the closure heads (Vessels No. 1, 4, 

6, and 8) and noted the possibility of cracks in the lid of Vessel No. 2. The cracks were 

found near the machined surface of the transducer hole in the vessel lid. The consultant 

determined that the leak was caused by stress corrosion cracking and was present in four 

of the vessel heads. The consultant attributed the stress corrosion cracking to issues in the 

design, material selection, and heat treatment of the vessels and vessel lids. 

4.2.1.1 Operating Warnings Prior to Incident

As a result of the vessel lid failure investigation, in July 2007 the consultant hired by NDK’s 

insurance company notified the insurer it had “serious reservations” about returning any 

of the vessels to service, specifically Vessels No. 3 and 5, and a decision to do so would be 

a “seriously flawed decision and not based on sound engineering analyses.” The consultant 

also cautioned that “far more catastrophic scenarios” involving the vessels were possible, 

17 An ingot is a mass or block of metal before casting or forging.

18 American Society of Mechanical Engineers (ASME). 2001, Specification for Alloy Steel Forgings for High-Strength Pressure Component 

Application, SA-723/SA-723M-2001. ASME Boiler and Pressure Vessel Code Section II Part A. New York, NY.
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NDK Crystal Case Study Final Investigation Report November 2013

imposing a hazard on NDK and the public, “including anyone who might be at the Belvidere 

Oasis on the Northwest Tollroad.” As a result, the insurer notified NDK of the consultant’s 

findings and reserved the right to deny claims for any future damages or consequences from 

the vessels (Appendix B). Despite this communication, NDK continued to operate the seven 

remaining vessels with intact lids, without performing thorough inspections of the vessel 

bodies by a certified professional. As of the publication date of this case study, the insurance 

company has not paid claims for the losses incurred by the 2009 explosion.

Even though the exact mechanism of failure for the vessel lids may have been different from 

the December 2009 rupture, the January 2007 incident and the results of the metallurgical 

examination should have prompted a closer examination of the vessel interior. The SCC on 

the lids was the first indication that the protective capability of the acmite coating was less 

than adequate, possibly throughout the entire vessel. Because the forging supplier produced 

the lids from the same ingot as the vessels, it was possible that a similar failure mechanism 

was acting on the vessel interior. The consultants investigating the lid failure indicated 

that the inner diameter was susceptible to cracks due to higher tensile hoop stresses down 

the length of the cylinder where caustic could concentrate in a surface notch or crack. 

The metallurgists commissioned by the CSB found NDK could have easily detected cracks 

in the vessel sample by non-destructive test methods, had the company performed such 

examinations. CSB investigators reviewed documents obtained by the insurance company and 

learned NDK was in the process of getting cost estimates for vessel body replacements at the 

time of the 2009 explosion.

4.2.2 Inspections

When NDK petitioned the State Boiler and Pressure Vessel Safety Division to get authorization 

to operate Vessels No. 1 through 3, the vessel designer from EPSI recommended annual, 

non-destructive inspections of the vessel interior. 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 entire length of the vessel interior.

After the 2007 lid investigation, the consultant hired by the insurance company recommended 

NDK perform inspections on the vessels prior to continuing operations. The consultant 

recommended a thorough interior examination of the vessels to identify cracks, as well as 

a Fitness-for-Service evaluation under the ASME and American Petroleum Institute (API) 

Recommended Practice 579.19 NDK contracted a metallurgical consultant to perform 

an ultrasonic inspection only on the top portion of Vessel No. 1 and found no internal 

discontinuities. Despite these 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 SCC identified by the consultant. 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. 

In addition to the vessel inspections, there were several recommendations submitted by the 

insurer in 2008 that remained unfulfilled at the time of the incident. NDK’s approach to 

safety was informal, lacking formalized job training, standard operating procedures, and an 

incident and injury notification and investigation program. 

19 Fitness for Service (FFS) assessment using API Recommended Practice 579 is performed to assess the operational safety and reliability 

process plant equipment.
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NDK Crystal Case Study Final Investigation Report November 2013

4.3 CODES AND STANDARDS

4.3.1 ASME

The American Society of Mechanical Engineers (ASME) is a not-for-profit professional 

organization that develops codes and standards that cover many technical areas in 

mechanical engineering practice and provides professional development programs. 

The ASME Boiler and Pressure Vessel Code (BPVC) provides requirements for the design, 

fabrication, inspection, and certification of boilers and pressure vessels. The State of 

Illinois adopted the ASME BPVC in 1976.

4.3.1.1 Material Specifications

The BPVC Section II, Part A includes ferrous material specifications for pressure-retaining 

components. Within Part A, ASTM Standard SA-723, Standard Specification for Alloy Steel 

Forgings for High-Strength Pressure Component Application, covers the requirements for 

materials used for forging and heat-treated high-strength vessels like the crystal-growing 

vessels at NDK. It includes the chemical requirements for three primary classes of steel with 

six sub-classes based on increasing tensile strength (Appendix A). 

The metallurgical examination commissioned by the CSB verified, through a chemical analysis 

of the sample, the material in Vessel No. 2 conformed to the chemical specifications as required 

by ASME. The three state special vessels at NDK could not meet the Charpy toughness levels 

required by ASME at 70°F, but did pass the Charpy tests at 212°F. 

NDK and the vessel designer selected a vessel thickness that exceeded the typical thickness 

limit specified in the ASME Code. Table 2 and 3 of SA-723 state the “typical maximum 

section size” is 7 inches for closed-end vessels. The thickness limitation exists to ensure 

proper heat treatment is achieved. The NDK vessel cylindrical shell is 8 inches thick, and 

the top and bottom portions of the vessel had a thickness of 18 1⁄4 inches at the lid and 

16 1⁄4 inches at the base. An analysis of the 8-inch thick Vessel No. 2 fragment microstructure 

did not show any evidence of a heat treatment issue; however, the 2007 examination of the 

18-inch thick vessel lids revealed large grain sizes, indicating faulty heat treatments may 

have been present in the thicker sections of the vessels, such as the lids and the base. 

The BPVC Section VIII Division 3, Alternate Rules for Construction of High Pressure Vessels, 

applies to vessels operating at pressures greater than 10,000 psig, such as the vessels at NDK. 

This section of the BPVC does not include specific limitations of material thickness for the 

design of heavy pressure vessels made with carbon and low-alloy steels, such as the Grade 

2 steel used at NDK. Article KM-400,20 Material Design Data, includes a table of required 

mechanical properties for each material covered under the section. The material listing used 

for the state special vessels has no required thickness limit. 

4.3.1.2 Requirements for Corrosion Prevention

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. Article KG 

311.7, Material Selection, in Section VIII Division 3 of the 2001 ASME code used for 

the design of the NDK vessels, required “appropriate materials for resistance to process 

corrosion including environmentally induced corrosion cracking.”21 In the user design 

20 ASME 2001, Alternate Rules for Construction of Pressure Vessels, KCS-1 Carbon and Low Alloy Steels, UNS K34035. ASME Boiler and Pressure 

Vessel Code, Section VIII, Division 3. New York, NY.

21 ASME 2001, Alternate Rules for Construction of Pressure Vessels, Article KG 311.7, ASME Boiler and Pressure Vessel Code, Section VIII 

Division 3. New York, NY.
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package for the state special vessels, the documentation from the vessel designer states, 

“Designation of material by user for corrosion resistance: None specified” in response to 

the Section VIII Article KG 311.7 requirements for corrosion prevention.

In a subsequent issuance, ASME revised Section VIII of the code related to material design 

and selection of pressure-retaining materials. The BPVC Section VIII, Division 3, Article KM400, Material Design Data,22 lists requirements for materials used in the fabrication of vessels, 

such as material limitations and mechanical properties. It contains additional requirements 

and cautionary statements listed for the Grade 2 Class 3 material used at NDK:

(17) Caution is advised when using the material above 700 deg F. After exposure to 

temperatures above 700 deg F, this material may exhibit temper embrittlement and stress 

relaxation defects. The designer shall consider these effects and their influence on the vessel.

(21) Caution is advised when using these materials, as they are more susceptible 

than lower strength materials to environmental stress corrosion cracking and or 

embrittlement due to hydrogen exposure... The designer shall consider these effects 

and their influence on the vessel.

(22) These materials shall not be used for applications when the material, when loaded, is 

in contact with water or an aqueous solution

a. These materials are permitted if the material is protected from contact by water 

or an aqueous environment...

Based on the changes to the ASME code, the appropriate code enforcing authority can 

prohibit the use of vessels similar to those at NDK with aqueous environments. 

4.3.3 NACE International

NACE International (National Association of Corrosion Engineers)23 is a global 

organization that offers training, certifications, industry standards, and publications 

related to corrosion prevention. NACE membership includes a broad range of industries, 

and NACE corrosion prevention standards are referenced or adopted by other codes and 

industry consensus standards such as API, ASTM, and pipeline safety regulations.

The NACE Standard, Avoiding Caustic Stress Corrosion Cracking of Carbon Steel Refinery 

Equipment and Piping (SP0403-2008), establishes guidelines to prevent SCC when using 

caustics, particularly aqueous sodium hydroxide. NACE has published guidance for handling 

sodium hydroxide since the mid-1960s. Though mostly used in refinery applications, the 

guidelines and precautions in this standard specifically address carbon steel components, but 

can also apply to the material used in the vessels at NDK. The increased design strength of 

the low-alloy steel vessels made them more susceptible to corrosion. 

The NACE standard states, “Caustic concentrations greater than 5 weight percent in the 

aqueous phase can produce SCC in carbon steel. Caustic SCC sometimes occurs in services 

with lower bulk fluid concentrations, usually in areas where local concentration effects 

occur.” NDK put 4 percent caustic in the NDK vessel. The standard also states that carbon 

steel is not suitable for use at temperatures greater than 215°F unless a nickel alloy is used.24 

22 ASME 2007, Alternate Rules for Construction of Pressure Vessels, Article KG 311.7, ASME Boiler and Pressure Vessel Code, Section VIII 

Division 3 -2008 Addenda. New York, NY.

23 Corrosion engineers in the pipeline industry originally founded NACE as the National Association of Corrosion Engineers in 1943.

24 NACE International. Avoiding Caustic Stress Corrosion Cracking of Carbon Steel Refinery Equipment and Piping, Caustic Soda Service Chart 

SP0403. Houston, TX, 2008.
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NDK relied on the acmite coating to act as an impervious barrier between the caustic 

environment and the inner surface of the vessel. According to the NACE Standard, organic 

or inorganic coatings may be applied but care should be taken to ensure the coating performs 

acceptably during process operations, shutdown, and cleaning. However, the acmite was a 

coating formed during the crystal growing process to improve product quality; it was not 

specifically applied to the vessel for corrosion prevention. 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 SCC issues 

on the lid material prior to putting the vessels back into service. This 2007 lid incident was the 

first indication the acmite coating was not providing complete corrosion protection. 

5.0 REGULATORY ANALYSIS

5.1 IOSHA

The Illinois Regional Office of the Occupational Safety and Health Administration (IOSHA) 

investigated the December 2009 incident and in May 2010 issued several serious and 

willful citations to NDK. Though NDK employees were not hurt during the incident, IOSHA 

concluded NDK employees were exposed to the potential hazards associated with the crystal 

growing process in the absence of documented safety training, hazard communication for 

process chemicals, and emergency and evacuation procedures.25 IOSHA also found that NDK 

did not complete a workplace hazard assessment for personal protective equipment. IOSHA 

cited NDK serious and willful violations under Section 5(a)(1) General Duty Clause,26 for not 

evaluating the NDK building for explosion hazards using recognized industry practices, 

and for choosing to return the vessels to service after the 2007 lid examination showed 

evidence of a material defect. 

5.2 IEPA

Following the December 2009 explosion, the Illinois Environmental Protection Agency 

(IEPA) proceeded with enforcement action against NDK for possibly polluting the soil, air, 

and groundwater with the sodium hydroxide solution released from Vessel No. 2 and the 

containment tanks during the explosion, and with the synthetic quartz crystals that may 

have released from the ruptured vessel. The State Attorney General filed a complaint against 

NDK following the explosion for alleged violations of the Illinois Environmental Protection 

Act.27 IEPA issued violations for a substantial endangerment to the environment and air 

pollution. NDK entered into a consent order with the IEPA to settle these claims and agreed 

to participate in several compliance activities approved by the IEPA. NDK contracted with 

an independent environmental consulting company to collect samples, conduct an analysis 

of those samples to estimate the identity and quantity of process chemicals released to the 

environment during the explosion, and submit the report to the IEPA.

The environmental consultants determined through sampling collection, testing, and analysis 

that accumulations of dust in and around the NDK facility following the incident consisted of 

building construction materials disturbed during the explosion. Information from the sample 

tests was insufficient to determine if silica from the lasca was released during the explosion. 

25 The NDK Crystal facility was not subject to the requirements of the Process Safety Management (PSM) Standard because the process did not 

contain significant quantities of listed hazardous materials or flammables.

26 Under the OSH Act of 1970, Section 5(a)(1), known as the General Duty Clause, states: “Each employer shall furnish to each of his employees 

employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical 

harm to his employees.”

27 Illinois Compiled Statutes, Environmental Protection Act § 415 ILCS 5.
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Soil surface pH measurements were slightly influenced by the release, but the consultant 

concluded that the materials released during the explosion would not cause adverse 

environmental or health exposure risks.

IEPA imposed a civil penalty of $39,000 on NDK. The company also paid response costs 

totaling $10,000 to the IEPA and Boone County. IEPA further required that NDK not 

resume operating the pressure vessels unless the IL State Fire Marshal’s office certified the 

vessels as safe for operation. The Attorney General also required NDK to submit a copy 

of the CSB investigation report on the NDK explosion, following publication. 

5.3 STATE BOILER AND PRESSURE VESSEL INSPECTOR 

The Division of Boiler and Pressure Vessel Safety within the Office of the Illinois State 

Fire Marshal regulates the construction, installation, operation, inspection, and repair 

of boilers and pressure vessels in Illinois. Illinois has over 100,000 boilers and pressure 

vessels registered and inspected on a routine basis by authorized, commissioned inspectors. 

In 1976, the state enacted the Boiler and Pressure Vessel Safety Act to establish the 

requirements of the division.28 The Boiler and Pressure Vessel Safety Act applies to steam 

boilers, hot water boilers, and pressure vessels and includes requirements for inspector 

competencies, vessel inspection intervals, and state special pressure vessels. Under the act, 

the Division of Boiler and Pressure Vessel Safety adopts the ASME code and the National 

Board Inspection Code (NBIC). The NBIC is an American National Standards Institute 

(ANSI) code for boiler and pressure vessel inspectors, which provides standards for the 

installation, inspection, and repair of boilers, pressure vessels, and pressure relief devices.29

It is adopted by the State of Illinois and establishes the requirements for all boiler pressure 

vessel inspections and repairs in the state.

The Boiler and Pressure Vessel Safety Act requires that pressure vessels subject to internal 

corrosion receive a certificate of inspection every three years.30 However, when the NDK 

vessels received their initial certification from the state, the Board of Boiler and Pressure 

Vessel Safety approved the vessels for non-corrosive service. As a result, the State Boiler 

and Pressure Vessel Inspector only inspected accessible external surfaces and pressure 

relief devices. The State Inspector conducted an external visual inspection of Vessel No. 2 

in 2003 and 2006 and finally on September 16, 2009, less than three months before the 

incident. According to the Boiler and Pressure Vessel Safety Act, internal inspections are 

not required of pressure vessels containing materials that are known to be noncorrosive 

to the materials of construction, either from the chemical composition of the materials 

or from evidence that the materials are adequately treated with a corrosion inhibitor.31

The caustic sodium hydroxide solution used at NDK is known to be corrosive to carbon 

steel. However, the Board of Boiler and Pressure Vessel Safety did not thoroughly examine 

the impact of the service fluid on the vessel during the meeting when NDK petitioned the 

state to use the vessels, or during the independent review of the vessel design package. 

When NDK petitioned the board to grant “state special” authorization, the designer from 

EPSI recommended annual, internal inspections such as magnetic particle and ultrasonic 

28 Illinois Compiled Statutes, Boiler and Pressure Vessel Safety Act § 430 ILCS 75. 

29 The NBIC is developed by the National Board of Boiler and Pressure Vessels Inspectors (NBBI). NBBI is an organization composed of chief 

boiler and pressure vessel inspectors throughout North America. Its purpose is to promote safety and education through training, enforcement 

guidance, and the development of applicable standards. 

30 Illinois Compiled Statutes, Boiler and Pressure Vessel Safety Act § 430 ILCS 75(10)(a)(4).

31 Illinois Compiled Statues, Boiler and Pressure Vessel Safety Act § 430 ILCS 75(10)(a)(5).
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examinations to ensure corrosion was not occurring inside the vessels.32 Despite this 

recommendation, 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.

5.4 THE CITY OF BELVIDERE

The land that NDK currently occupies was originally undeveloped agricultural land. The 

land was designated as residential until 1996, when the City of Belvidere granted a zoning 

district change of about 200 acres of land to light industrial, office, and research space for 

economic development (Figure 15). 

In 2001, NDK petitioned the City of Belvidere to permit the construction of its proposed 

office and manufacturing facility. After scheduled hearings with the Belvidere Planning and 

Zoning Commission, and Building Department, the City granted NDK a permit and zoned 

the proposed NDK location as “light industrial.” NDK purchased a lot in the light industrial 

district near the I-90 Tollway Oasis. 

The City zoned the NDK lot and the surrounding area as light industrial in accordance 

with the 1994 Belvidere Zoning Code that was adopted by the City at the time. The 

objective of the 1994 Belvidere Zoning Code was to protect and promote public health, 

safety and general welfare for the citizens of the city, including the prevention of bodily 

harm to persons or property by fire, toxic fumes, explosions, or other hazards.33

The 1994 Zoning Code defined light industrial districts as appropriate for “uses that will have 

a minimal detrimental effect on surrounding properties.”34 Light industrial districts included 

manufacturing and production operations, but excluded any of the uses permitted only in 

&)'52% 

 ,IGHT
)NDUSTRIAL

:ONING LOCATION NEAR

NDK Crystal.

32 Proceedings from the IL State Fire Marshal Meeting, June 5, 2002, T20-3.

33 1994 Belvidere, Illinois, Code of Ordinances, § 150.001(h).

34 1994 Belvidere, Illinois, Code of Ordinances, § 150.0016(a).
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the heavy industrial districts.35 Though synthetic quartz manufacturing is not specifically listed in the 

heavy industrial uses, the temperatures and pressures involved in this operation are similar to the 

heavy industrial processes listed in the code, such as the production of coal, coke, and tar; gas 

manufacturing; petroleum refining processes; metal and metal ore refining; power and steam 

generation; and paint and rubber manufacturing.36

Due to the height of the proposed NDK facility, the City required a special-use permit. According 

to the Belvidere code, when considering a special use permit, the planning commission shall take 

into consideration several criteria prior to approval, including the protection of public health and 

general welfare, and that the special use will not cause substantial injury to the value of proposed 

locations or other property in the neighborhood.37

CSB reviewed records from the City of Belvidere Planning and Zoning Commission and 

Building Department. According to the City of Belvidere’s summary of findings in the specialuse permit documentation, there was no evidence that the design, location, or proposed 

operation affected public safety. However, the City of Belvidere required compliance with all 

other applicable codes and ordinances as a condition for permit approval. The CSB found no 

documentation that the zoning commission considered the offsite consequences associated 

with the proposed operation of eight high-pressure vessels at the facility. The installation 

and operation of the pressure vessels for the manufacturing process was not included in the 

application or any documentation submitted to the City during the permitting process. 

6.0 KEY FINDINGS

1. Stress corrosion cracking likely caused the catastrophic rupture of a high-pressure crystal 

production vessel at NDK Crystal, Inc., fatally injuring a member of the public 650 feet away at 

a highway rest stop.

2. NDK relied upon the in-process formation of an acmite coating inside the production vessel 

to protect the low alloy, high-strength steel from caustic sodium hydroxide used in the 

manufacturing process. However, NDK did not verify the integrity or effectiveness of this 

coating, and the caustic chemicals promoted stress corrosion cracking that weakened the vessel.

3. 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. Instead, the state says it relied on the company to perform internal inspections, but 

it did not verify whether these were actually occurring. The state conducted three certificate 

inspections of the vessel that failed in 2003, 2006, and 2009 (less than three months prior to 

the incident) but these inspections focused only on accessible external surfaces.

4. In 2007, NDK learned that stress corrosion cracking was occurring in four of eight pressure vessel 

lids at the facility. A consultant to NDK’s insurance company warned NDK of “serious reservations” 

about returning the vessels to service after this discovery and specifically cited the possible danger to 

members of the public at the nearby rest stop in case of a catastrophic vessel failure. 

5. Despite the insurance company warning, NDK did not perform recommended non-destructive 

examinations of all vessels prior to returning the vessels to service.

6. NDK did not perform annual internal inspections as recommended by the vessel designer when 

the vessels were initially constructed.

35 1994 Belvidere, Illinois, Code of Ordinances, § 150.0016(b).

36 1994 Belvidere, Illinois, Code of Ordinances, § 150.0017(b).

37 1994 Belvidere, Illinois, Code of Ordinances, § 150.0024.
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7. Temper embrittlement, or some other form of heat treatment embrittlement, cannot be ruled out 

as a contributing factor in addition to the SCC. The vessels exceeded the ASME wall thickness 

recommendations for closed-end forgings, which may have resulted in improper heat treatment 

during the manufacturing process.

8. The ASME Boiler and Pressure Vessel Code does not have specific wall thickness limitations for 

pressure containing components. 

7.0 RECOMMENDATIONS

7.1 AMERICAN SOCIETY OF MECHANICAL ENGINEERS (ASME) 

2010-4-I-IL R1 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

7.2 NATIONAL BOARD OF BOILER AND PRESSURE VESSEL INSPECTORS (NBBI)

2010-4-I-IL R2 Communicate the findings of this Case Study to pressure vessel inspectors 

in all 50 states. At a minimum: 

a) Send the information (such as an article summarizing the investigation) 

to each member who is a pressure vessel inspector; and,

b) Post a direct link to the NDK Case Study on the National 

Board’s webpage.

7.3 OFFICE OF THE ILLINOIS STATE FIRE MARSHAL, BOILER AND PRESSURE VESSEL SAFETY DIVISION

2010-4-I-IL R3 Prohibit the use of the existing pressure vessels at the NDK facility for 

crystal growing operations.

2010-4-I-IL R4 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.

7.4 NDK CRYSTAL, INC.

2010-4-I-IL R5 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).

2010-4-I-IL R6 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.
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2010-4-I-IL R7 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.

2010-4-I-IL R8 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.

APPENDIX A

TABLE 1 - CHEMICAL REQUIREMENTS

PERCENT COMPOSITION

Grade 1 Grade 2 Grade 3

Carbon, max 0.35 0.40 0.40

Manganese, max 0.90 0.90 0.90

Phosphorus, max 0.02 0.02 0.02

Sulfer, max 0.02 0.02 0.02

Silicon, max 0.35 0.35 0.35

Nickel 1.5 to 2.25 2.3 to 3.3 3.3 to 4.5

Chromium 0.80 to 2.00 0.80 to 2.0 0.80 to 2.0

Molybdenum 0.20 to 0.40 0.30 to 0.50 0.40 to 0.80

Vanadium, max 0.20 0.20 0.20

TABLE 2 - TENSILE REQUIREMENTS

Class 1 Class 2 Class 2a Class 3a Class 4 Class5

Tensile Strength, min, ksi 115 135 145 155 175 190

Yield Strength, 0.2% offset, min, psi 110 120 130 040 160 180

Elongation in 2 inches or 50mm, min, % 16 14 12.5 13 12 10

Reduction of area, min, % 50 45 43 40 35 30

A) Typical maximum section size of 10 in. for open-ended vessels, or 7 in. for blind-ended vessels
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APPENDIX B
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