United States Nuclear Regulatory Commission - Protecting People and the Environment


ACCESSION #: 9511270151



                       Investigation and Analysis

                                   of

                            Suspect Fasteners



                               Event 29257



                              Final Report



                               Prepared by

                      Cardinal Industrial Products

                 Division of B&G Manufacturing Co., Inc.



                             November, 1995



                              INTRODUCTION



On July 10, 1995, B&G Manufacturing Co., Inc. ("B&G") purchased the name

and certain other assets from Cardinal Industrial Products, L.P. ("CIP-

LP") a limited partnership formed and operated in Nevada servicing the

nuclear power industry.  B&G acquired these assets to begin its own

nuclear fastener business as a new division of B&G ("B&G-Cardinal").



Various owners have operated a nuclear fastener business under the

"Cardinal" name at West Oquendo Road in Las Vegas prior to B&G's

acquisition of assets from CIP-LP on July 10, 1995.  In this report the

term "Cardinal facility" is used to describe the general operations which

have continued at that site independently of ownership.  The reader is

advised to be aware of the nature and sequence of the ownership as this

report is reviewed.



Shortly after July 10, 1995, Duquesne Light notified B&G-Cardinal about

nonconforming Grade B7 hex capscrews, which had been processed and sold

to them by CIP-LP.  Several of the suspect fasteners were tested by B&G-

Cardinal and an independent testing laboratory and found to deviate from

SA 193, Grade B7 mechanical requirements.  Although these fasteners had

been processed, sold, and shipped by CIP-LP, B&G sent notifications of

the nonconformance to the NRC and to other purchasers of product from the

same lot.  As a result of the notifications, two other utility companies

reported to B&G-Cardinal nonconforming fasteners from the same lot and

one additional lot.



B&G initiated a comprehensive investigation to ascertain the scope and

cause of the problem, to determine corrective actions, to keep its new

customers fully informed and, as a courtesy, to be able to instruct them

to evaluate the condition in light of 10CFR Part 21 paragraph

21.21(a)(1)(ii) and (b)(1).



Metallographic analysis of the nonconforming fasteners indicated improper

heat treatment, which prompted B&G-Cardinal to begin testing similar lots

of material from inventory that were manufactured using the same heat

treatment process.  This testing revealed additional nonconforming

product and thereby indicated the problem was not isolated to only one

lot but was related to the process.



Investigation and testing traced the problem to the heat treating furnace

at the Cardinal facility, and substandard fasteners most likely can be

isolated to eight lots of material processed since 1989.  (The

investigation could not address product processed prior to 1989 because

records were unavailable.)



Final Report 11/95                                                 Page 1



 This report describes the problem, the investigation strategy, testing

and analysis, and other actions taken by B&G-Cardinal that revealed the

source of the defects to be processing deficiencies in heat treating

certain material at the Cardinal facility.



                               THE PROBLEM



Certain lots of hex capscews that were processed and shipped per ASME SA-

193, Grade B7 out of the Cardinal facility by CIP-LP were found to

contain defective fasteners.  The problem was initially discovered by

Duquesne Light's Beaver Valley facility, which had sent several 3/8"

diameter capscrews to an outside laboratory for random verification

testing.  The results of these tests indicated some fasteners from the

lot were not in compliance with the mechanical requirements of the

specification.  Duquesne Light reported this failure to B&G-Cardinal.

Independent test reports from the Beaver Valley facility (and later from

PG&E Diablo Canyon and Washington Public Power Supply System) suggested

the fasteners in question had not been properly heat treated.



The suspect lot of ASME SA-193 Grade B7 capscrews was manufactured at the

Cardinal facility from AISI 4140 medium carbon alloy steel.  The

manufacturing process utilized by CIP-LP was to cold form capscrews from

spheroidized annealed cold heading wire.  The fasteners were then heat

treated by a process of either normalizing, quenching, and tempering, or

simply by quenching and tempering.  Depending on the lot sizes, the heat

treatment was either performed at the Cardinal facility or by an approved

outside vendor.



                            IMMEDIATE ACTION



To verify the testing results obtained by Beaver Valley, B&G-Cardinal

performed tensile and hardness tests on capscrews from the same lot.

These tests were performed at the Cardinal facility's laboratory under

the direction of B&G-Cardinal's Quality Assurance Department.  The

mechanical properties of several of the capscrews tested were found to

deviate from the minimum requirements of Grade B7.  This lot of material

was immediately removed from stock, marked as nonconforming, and isolated

in the nonconformance room.



Samples of both conforming and nonconforming fasteners were sent to an

outside laboratory for metallographic examination.  The examination of

the conforming fasteners indicated the fasteners had the tempered

martensite structure expected from proper heat treatment.  The

nonconforming fasteners, however, had a spheroidized structure that

indicated the heat-treated fasteners had not reached the temperature

required for the martensite structure to form.



Final Report 11/95                                                 Page 2



Because the nonconforming lot was heat treated at the Cardinal facility,

B&G-Cardinal decided to concentrate its investigation on the heat

treating equipment and process there.



                            THE INVESTIGATION



Early indications suggested that the nonconforming fasteners had never

been heat treated.  The lot in question weighed over 250 pounds and would

have been placed in several containers for ease of transport through the

Cardinal facility, so it was plausible that a lone container of fasteners

had bypassed heat treatment and was later intermingled with the rest of

lot, which had been heat treated.  B&G-Cardinal then sampled a large

number of the fasteners still in inventory from the suspect lot and

found, however, substandard fasteners with visible surface scale, which

indicated that all the fasteners, including suspect ones, had been heat

treated.



Because the fasteners definitely had been heated in the furnace, the

focus of the investigation turned to the heat treatment process and

equipment at the Cardinal facility.  Recognizing that a problem with the

heat treating facility may have affected other lots of material, the

Quality Assurance Department began sampling other lots from inventory

that had been heat treated through the furnace at the Cardinal facility.



During the investigation, B&G-Cardinal sent courtesy notifications to the

NRC and to companies which had purchased capscrews from the questionable

lot.  Within a few days of these notifications, PG&E Diablo Canyon

informed B&G-Cardinal of a substandard, 3/8" diameter capscrew that had

come from a second lot.  In addition, the inventory sampling process by

B&G-Cardinal revealed a third and fourth lot that contained substandard

fasteners of 3/8" and 5/8" diameters, respectively.  Courtesy

notifications were also sent regarding these lots.



It became apparent that the four lots found to have substandard fasteners

all entered the furnace in "large" charges held at a temperature for

"short" periods (relative to other charges performed at the Cardinal

facility).  The period in question was the duration parts were held in

the furnace ("soaked") at the specified temperature for austenitizing

just prior to lowering the basket of parts into a quench tank.  The

soaking time for A/SA 193, Grade B7 product must be long enough to allow

all parts to achieve an austenitic microstructure prior to quenching them

rapidly in a liquid medium at a controlled temperature of 125 degrees F.

The quenching provides a rapid temperature drop that results in the

formation of a primarily martensitic structure.  After quenching, parts

should register hardness values of approximately 50 on the Rockwell C

scale and tensile strengths between 225,000 and 300,000 psi.  The parts

then undergo a tempering cycle that entails heating them to a



Final Report 11/95                                                 Page 3



1,100 degrees F minimum followed by a slow cooling process.  Tempering

reduces the tensile strength and develops ductility as required (for A/SA

193, Grade B7, a minimum tensile strength of 125,000 psi with ductility

exhibiting 16% minimum elongation and 50% minimum reduction of area).



Two primary problems can occur with the heat treating cycle.  First, the

charge may not be allowed to "soak" in the furnace long enough for all

the fasteners to reach the temperature required to achieve an austenistic

microstructure.  Second, the parts may not cool rapidly enough if the

liquid quenching medium is not circulating sufficiently enough to provide

adequate heat transfer in the required amount of time.  The lots in

question were processed in heat charges of relatively heavy weight, which

could be a potential factor in either problem.  If the charge size was

too large, some or all the parts may not have reached the required

temperature in the given time period; or the temperature of the quenching

liquid may have become too high to accomplish the required rapid cooling

by the time the liquid reached the parts at the center of the charge upon

being lowered into the quenching tank.



Heat treatment logs for charges performed at the Cardinal facility dating

back to 1989 were included in the records obtained by B&G-Cardinal from

CIP-LP.  B&G-Cardinal examined these logs, which showed since 1989 a

total of 333 charges were heat treated involving AISI 4140 medium carbon

alloy steel.  The data for each of these charges was entered into a

spreadsheet and then sorted in descending order by weight and time

(pounds per hour) with the expectation that the worst case charges

(heavier charges or shorter soak times) would appear first (See Addendum

1).  The charge with the previously identified 5/8" lot with known

substandard fasteners was at the top of the list, and the other three

3/8" lots were all within the first 13% of charges listed.  The pattern

of sorted data was as anticipated and indicated that sound metallurgical

principles were taking investigation in the proper direction.



Most of the product identified in the heat treatment log had been sold

and shipped prior to B&G's purchasing assets from CIP-LP, therefore lots

generally were not available from inventory for testing.  Thus, the

strategy of investigation was to recreate the heat treating conditions

that would produce known defects.  Test charges were planned using times,

temperatures, and weights identical to the heat charges known to have

produced defective product.  Other test charges were devised with the

purpose of determining what combinations of weight and soak times would

result in defective product.  From the heat treatment log, charges with

extreme weights relative to soaking times were identified for each

diameter of Grade B7 capscrews, and product was either manufactured or

taken from inventory to be used for the test charges.



Final Report 11/95                                                 Page 4



Over a two week period, 22 test charges were heat treated.  After each

charge, test coupons were removed from specific locations within the heat

treatment basket and were tested for hardness (See Addendum 2).  From the

results of the early test charges, the following hypotheses were formed:



     1.   Some of the fasteners in the basket were not reaching the

          required temperature in the allotted time.  This conclusion was

          based upon the location of the substandard fasteners found in

          failed test charges.  This hypothesis is supported by two

          separate metallographic examinations of substandard fasteners.



     2.   The time required for all fasteners in the charge to reach

          temperature is dependent upon charge density as well as overall

          weight.  Charge density is a function of the fastener's

          dimensions where 3/8" diameter fasteners will pack more densely

          than 5/8" diameter fasteners.



In addition to performing tests to verify the integrity of past charges,

other charges were specifically performed to verify the above hypotheses.



Because the problem appeared to relate in general to heat transfer and

not necessarily to any specific material, the investigation was broadened

to include all heat treated materials.  The heat treatment logs were

again reviewed, but without regard for material or heat treatment type

but rather simply for what appeared to be the critical indicators of

weight, time at temperature, and charge density.  No other charges were

found to have critical factors in the range which coincided with test

charge failures.



During the investigation, the possibility of a problem with the quenching

phase of the heat treating cycle was dismissed based upon metallographic

analysis.  The metallography comparisons of acceptable and substandard

fasteners taken from the same lot showed two clearly different but

identifiable microstructures.  The photomicrograph of the acceptable

fastener showed the proper tempered martensite microstructure with some

retained austenite.  The microstructure of the substandard fastener was

spheroidized carbides in a ferrite matrix, which results only when alloy

steel does not reach the austenitizing temperature.  Either

microstructure was dependent upon proper quenching.  In other words,

inadequate quenching in either case would have produce yet another

identifiable microstructure.



Final Report 11/95                                                 Page 5



                         INVESTIGATION FINDINGS



In the process of performing of 22 different quench-cycle test charges,

B&G-Cardinal was able to recreate heat treatment conditions and

substandard fasteners corresponding to the four inventory lots known to

have contained substandard fasteners.  Because these test charges

produced the expected results and thereby substantiated the hypotheses,

B&G-Cardinal ceased investigating other causes.  In addition to the test

charges that recreated known failures, other test charges produced

substandard fasteners that paralleled four additional lots of material

from the heat treatment log.  While there is no conclusive evidence that

corresponding actual production charges contained substandard fasteners,

it was likely they did; therefore, B&G decided to send courtesy

notifications to the NRC and known customers for these lots, too.  The

other 14 test charges done under the remaining worst-case conditions

produced acceptable results and therefore strongly suggests that

substandard fasteners can be isolated to the eight lots of inventory for

which simulated heat-treatment charges produced failures.



The test charges containing substandard fasteners were evaluated by

hardness testing of forty coupons taken from specific locations from

throughout the charge.  The hardness readings were documented on forms

which detail the location of each coupon (See Addendum 2).  Based upon

the map of the hardness readings, it is apparent that the bottom layer of

fasteners near the center of the basket was the last to reach temperature

in larger lots.  The primary heat transfer mode for the furnace is

radiation.  The secondary heat transfer mode is conduction.  In large

charges of densely packed fasteners, conduction becomes much more

important.  Because of the configuration of the furnace at the Cardinal

facility, the bottom center portion of the basket did not receive

significant heat through radiation.  Fasteners at the bottom layer

received their heat through conduction from the upper layers of

fasteners.  In the charges containing substandard fasteners, the time

required for the heat to reach the bottom layer of fasteners was longer

than the fasteners remained in the furnace.



This problem was not discovered earlier because the test coupons that had

been used by the Cardinal facility for tensile and hardness testing were

typically placed at the top, center spot of the charge.  Had the test

coupons been placed within the area of the charge which failed to reach

temperature because of lagging heat transfer, the defects could have been

detected during the normal testing performed on heat charges.



The furnace at the Cardinal facility takes approximately two hours to

reach the appropriate austenitizing temperature for A/SA 193, Grade B7.

After this temperature is reached, the fasteners are allowed to "soak" at

temperature for at least one hour.  The soak time is intended to provide

even distribution of the heat.  The furnace's thermocouple used to



Final Report 11/95                                                 Page 6



register its temperature is positioned in the upper region of the furnace

(See Addendum 3).  The results of the test charges demonstrated that not

all the contents of a charge reach the indicated temperature at the same

time.  The time required for the bottom layer of fasteners to reach

temperature was affected by the weight of the charge and the charge

density.



One of the test charges that failed (#21) was 331 pounds of 3/8" x 1"

long capscrews.  This charge contained nearly 8,000 pieces and was only 2

1/2 inches deep in the basket (the basket is 37 inches long and 25 inches

wide).  Another charge of the equivalent weight (#5) passed but contained

5/8" x 2 1/2" and 5/8" x 3" long capscrews.  This charge contained just

over 1,100 fasteners and was 4 1/2 inches deep.  How densely fasteners

were packed in the charge affected the amount of heat received through

radiation as compared to conduction.  In general, the smaller the

diameter of the fasteners, the more the charge acts as a solid mass.  In

both of the above listed examples the charge was held at temperature for

one hour, but the charge that failed had 3/8" diameter fasteners that

packed more densely than the charge that passed with the larger, 5/8"

diameter fasteners.



In another example, the diameter of the test charge was held constant and

packing density was changed.  300 pounds of 3/8" x 1" long capscrews were

held at temperature for one hour and contained no bad fasteners (test

charge #19).  Another charge (#22) contained 270 pounds of 3/8" x 4"

capscrews and was also held at temperature for one hour.  The four-inch

long capscrews; of this lot were carefully lined in rows when packed into

the basket (which is a common practice to prevent shank warpage).  The

tightly packed charge of four-inch long screws contained failed

fasteners.



                        INVESTIGATION CONCLUSIONS



The conclusion of this investigation is that the substandard fasteners

resulted from procedural error involving the time that heat treatment

charges were held at temperature for the given conditions, specifically

the charge's weight and density as determined by the diameter of the

products and method of packing.  According to the records left behind by

CIP-LP, the standard practice of CIP-LP for heat treating operations

referred to Military Standard MIL-H-6875.  However, the CIP-LP's standard

practice made no reference to factoring the overall weight or packing

method when determining the correct soaking time for a particular charge

in the furnace at the Cardinal facility.



The heat treatment equipment located at Cardinal facility does have

limitations.  In general, the furnace has heating elements on four sides

and on the ceiling (See Addendum 3).  This would not be a problem except

that the single thermocouple is located in the ceiling of the furnace.

The temperature indicated on the display panel and recorded on the strip

chart



Final Report 11/95                                                 Page 7



may not reflect the temperature throughout the furnace and the charge.

This limitation, however, could have been compensated for procedurally by

allowing charges to remain at temperature for longer periods of time.



B&G-Cardinal has been asked what the percentage of fasteners is

substandard in the suspect, and what is the strength of the substandard

fasteners.  It should be assumed that the heat treatment of any of the

suspect lots was insufficient to achieve the mechanical properties of

A/SE 193, Grade B7, and that the mechanical properties of the fasteners

from those lots are equivalent to annealed AISI 4140 material.  This

means the tensile strength is between 60,000 and 70,000 psi.  Estimating

the percentage of fasteners that are substandard in a given lot is much

more difficult.  Basing estimates upon heavy charges having five or six

layers of capscrews with as many as fifty percent of the bottom layer

being substandard suggests that the lot would contain 10 percent

defective fasteners.  However, one cannot assume that substandard

fasteners are distributed evenly throughout a total lot; defective

fasteners, for instance, could have been concentrated into one container

when packed for warehousing or shipping.  Therefore, B&G-Cardinal cannot

conclusively say what percentage of fasteners purchased by any particular

customer was substandard.



There are two other factors in connection with the heat treating

equipment at the Cardinal facility which would tend to isolate suspect

charges to the types of product and material investigated with the 22

test charges.



The first is the quenching medium, which is a polymer solution.  The

particular design of the quench tank located at the Cardinal facility

precludes the use of oil because it would be a fire hazard.  The polymer

solution is a suitable alternate for oil for many materials such as A/SA

193 Grade B7.  But a polymer solution cannot be used in the heat

treatment of very high strength materials such as A490 structural bolts,

A574 socket screws, F912 set screws, or A354 Grade BD (SAE J995 Grade 8)

because these specifications require an oil quench.  A polymer solution

is also not suitable for quenching products made from medium carbon

steels, such as A325 structural bolts, A449 Type 1 (SAE J995 Grade 5)

bolts, A194 Grade 2H nuts, A563 Grade C, D, or DH nuts, and F436 flat

washers.  Consequently, there seems no reason to believe that any of

these types of products would have undergone heat treatment at the

Cardinal facility.



Secondly, rods and studs were generally not heat treated at the Cardinal

facility because they were produced from bars which already met

applicable specifications and did not require additional heat treatment.

In addition, the heat treatment basket could not physically accommodate

any studs or rods longer than 36 inches.



Final Report 11/95                                                 Page 8



B&G-Cardinal believes that the problem of substandard fasteners

discovered initially by Duquesne Light does not extend beyond the eight

lots of Grade B7 capscrews already identified through testing charges

based upon critical factors of weight, density, and soaking times; but

B&G-Cardinal cannot guarantee this conclusion.  Customers should evaluate

replacing any fasteners installed from these eight lots, and should

consider testing other lots if deemed necessary for further assurance.



                                 SUMMARY



Shortly after receiving notification from Duquesne Light that capscrews

sold to them by CIP-LP did not meet the specification requirements, B&G-

Cardinal began an investigation into the cause and scope of the problem.

During this investigation, a detailed review of records was performed as

well as a duplication of past heat treatment charges.  During the

investigation, B&G-Cardinal recreated the heat treating conditions of

suspect lots and through test charges successfully duplicated the

failures in four lots of material known to contain substandard fasteners;

additional test charges produced four more lots with substandard

fasteners, which may indicate that corresponding lots in the field may

also have substandard fasteners.



The cause of the problem was determined to be procedural error.  As a

courtesy, B&G-Cardinal has notified the NRC and the companies that

purchased capscrews from lots containing suspect material.



B&G-Cardinal has discontinued using the heat treatment equipment at the

Cardinal facility until such time that satisfactory modifications are

made to both the hardware and procedures governing the heat treating

operation.



Corrective action to preclude recurrence include, but are not limited to:



     1.   Revising or adding procedures to address minimum soak times,

          basket loading procedures, and placement of test specimens;

          upgrading training programs for operators of the furnace.



     2.   Adding a second thermocouple to the furnace located at the

          bottom-center of the furnace near the parts basket (where heat

          transfer can lag behind other sections of the furnace,

          depending on weight and density).



     3.   Adding a view port to the furnace so that the operator can

          observe the charge during the heat treatment.



Final Report 11/95                                                 Page 9



     4.   Considering overhauling or replacing the furnace if other

          corrective actions are insufficient.



                                ADDENDUMS



     1.   Sorted Heat Treatment Data Showing Heavy Charges

     2.   Test Charge Results

     3.   Heat Treatment Equipment at the Cardinal Facility



Final Report 11/95                                                Page 10



Table "Heat Treatment Log Charge Data - Sorted by Pounds per Hour",

Addendum 1, Pages 1 thru 7, omitted.



Table "Test Charge Results", Addendum 2, Page 1, omitted.



Table "As Quenched Heat Treat Charge Analysis", Addendum 2, Pages 2 thru

20, omitted.



                        Heat Treatment Equipment



General:  The heat treatment equipment at the Cardinal facility consists

of a basic electric furnace, a separate quench tank containing a polymer

solution, as well as several instrumentation and control systems.



Furnace:  The furnace has two main components, the base and the door.

The base is supported by a steel structure at a height of 4 1/2 feet

above the foundation (just lower than the top of the adjacent quench

tank).  The door is supported by the same structure, and moves vertically

to allow for insertion and removal of the parts basket.  The door

operates hydraulically with a total travel of approximately 30 inches.  A

rack supported by bricks rests in the center of the base.  The basket

containing the parts being heat treated is placed on the rack.  Both the

rack and the basket are made from Inconel.  The furnace door houses the

heating elements and the thermocouple.  There are eleven rows of heating

elements; two on each side and three across the ceiling.  Side views of

the furnace door and base are shown below as Figures 1 and 2.  Figure 1

is the view from the quench tank.  Figure 2 is the view from the side

perpendicular to the quench tank.



Figure 1 "Furnace Side View Facing Quench Tank" omitted.



                                                               Addendum 3

                                                                   Page 1



Figure 2 "Furnace Side View" omitted.



Figure 3 is a side view of the furnace with the oven door in the closed

position.  With the oven door closed, there is approximately 2 1/2 inches

of clearance between the top of the basket and the upper heating

elements.  The thermocouple protrudes eight inches from the ceiling and

extends into the basket approximately two inches.



Figure 3 "Furnace Door Closed" omitted.



                                                               Addendum 3

                                                                   Page 2



Figure 4 is a top view (and side view) of the base with the bottom of the

figure facing the quench tank.  The bricks used to support the rack are

arranged in a symmetrical pattern as shown.



Figure 4 "Top View of Base" omitted.



Figure 5 is a top view with the same perspective as Figure 4.  This view

shows the parts basket placed on the rack and a cutaway view of the door

showing the clearance between the basket and the side heating elements.



Figure 5 "Top View of Base with Basket" omitted.



                                                               Addendum 3

                                                                   Page 3



Figure 6 is a top view of the door as viewed from the base looking up.

The right side of the drawing faced the quench tank.  This view shows the

upper three rows of heating elements and the location of the

thermocouple.



Figure 6 "Top View of Door" omitted.



Quench Tank:  The quench tank is located adjacent to the furnace.  The

tank contains 2,390 gallons of a polymer based quenchant.  The polymer is

suspended in water and precipitates out onto the hot parts when they are

lowered into the tank.  This provides an insulative layer which controls

the rate of temperature drop.  The polymer returns into solution as the

parts cool.  The polymer is a suitable replacement for oil as a

quenchant, except for specifications which specifically state parts must

be quenched in oil.  The quenchant is circulated by an agitator assembly

located at the bottom of the tank.  The agitator ensures a continuous

flow of quenchant through the parts basket during the quench.  The

polymer quenchant in maintained at approximately 125 degrees F for

quenching A/SA 193 Grade B7 products.



Instrumentation and Controls:  The signal from the thermocouple is sent

to a control panel which automatically maintains the furnace temperature

by controlling the power to the heating elements.  The temperature is

maintained within a tolerance of +/- 15 degrees F.  The temperature

signal also feeds a strip chart recorder which plots temperature against

time.



Other:  The oven door, basket crane, and agitators are all operated by

individual hydraulic systems.



                                                               Addendum 3

                                                                   Page 4



*** END OF DOCUMENT ***



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