ML20138Q936
| ML20138Q936 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 09/20/1985 |
| From: | Dungan K, Lorenz M, Shearman R PROFESSIONAL LOSS CONTROL, INC. |
| To: | |
| Shared Package | |
| ML20138Q927 | List: |
| References | |
| TAC-60320, TAC-60321, NUDOCS 8511180342 | |
| Download: ML20138Q936 (14) | |
Text
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{C pgltOFESSIONAL LOSS CONTROL, INC.
ANALYSIS OF ELECTRAY HANGER RODS IN UNIT 1 MECHANICAL PIPE CHASE AT McGUIRE NUCLEAR STATION FOR DUKE POWER COMPANY Submitted: September 20, 1985 Prepared by: ,
Mark S. Lorenz M_C/
Fire Protection Engineer Revision: 1 Reviewed by: _O.
Randall J.~Shearman Fire Protection Engineer Approved by: ~ h[
KnnethW.Dungan,P .
President hhk G
DO [
P. O. Box 446 e Oak Ridge, Tenn.?ssee 37831 * (615) 482-3541
TABLE OF CONTENTS Section Subject Page 1.0 Area Description............................................. 1 2.0 Problem Statement............................................ 1 3.0 Combu s ti bl e Load i n g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 4.0 Analysis..................................................... 2 5.0 Conclusions.................................................. 6 6.0 References................................................... 7 Attachment A Area Sketch Attachment B Cable Insulation Information and Calculations Attachment C Yield Strer. th versus Temperature Graph 9
e b 9
ANALYSIS OF ELECTRAY HANGER RODS 1.0 AREA DESCRIPTION The area under consideration is the Unit 1 Mechanical Pipe Chase on the 716'-0" elevation of the Auxiliary Building. The bounding walls are constructed of reinforced concrete. The ceiling height in this
-area is greater than 30 feet. The large open area and the ceiling height will prevent the build up of a significant hot layer. There-fore, only fire plume effects need be evaluated. (See Attachment A for a sketch of the area under consideration.) There are no automatic suppression systems in the area, but smoke detectors are provided.
Portable fire extinguishers and hose stations are available for manual fire fighting operations.
2.0 PROBLEM STATEMENT The problem is to determine if electray hanger rods will lose their support strength due to elongation and possible subsequent failure of the rods due to the temperature of the fire below the rods. In the area are three electrays which contain power and control cables for certain motor operated valves. These valves may be required during certain shutdown operations. A three-hour fire resistive barrier wrap is installed on the electrays to prevent an exposure fire from damag-ing the cables in the electrays. The exposing cable trays are not wrapped. The postulated fire scenarios of concern are a fire in each of the three cable trays 4-6 feet below one of the electray hangers (see Attachment A) or floor level fires involving transient combusti-bles. ,
3.0 COMBUSTIBLE LOADING The area contains control and power cable trays. The predominant type of combustible in the area is cable insulation. Transient combusti-bles were considered. However, since the area is a normally (plant operating) unoccupied and locked high radiation area, the presence of 1
transient combustibles was considered to be unlikely. The total load-ing in the five (5) cable trays shown on Attachment A is 796 lbs. of cable insulation and the average tray loading is 5.27 lbs/ft2 of tray surface area. (See Attachment B for cable insulation calculations.)
Enclosed combustibles such as cabling in conduit and in wrapped elec-trays have not been considered in this analysis.
4.0 ANALYSIS This analysis was conducted in two parts; first, the quantification of the failure temperature of the electray supports, and second, the quantification of the fire exposure plume temperature. Because of the large surface area to mass ratio of the supports (rods), heat transfer to the supports was considered instantaneous and a failure would occur the instant the air temperature exceeded the rod failure temperature.
Manufacturer's data on the hanger rods indicates that for design, the maximum allowable load for a rod is 1,100 lbs. According to the manu-facturer, the safe load is much higher. Duke Power Company, however, has limited the maximum allowable load for a rod to 80 lbs. The 1/2" diameter,13 threads per inch hanger rods have an internal diameter of 0.45 inches. The rods are fabricated from low carbon, mild steel.
Using a loading of 80 lbs. yields a working stress of 503 psi or 0.5 ksi (thousand pounds per square inch).
Attachment C is an AISI graph (1) of yield strength of ASTM A36 steel (common mild carbon steel - yield strength GF 33 ksi) versus tempera-ture. From the graph we can see that as a fire approaches a tempera-ture of 1600*F, the yield strength of the steel member is in a range of 0-1 ksi. In order to obtain a precise temperature at 0.5 ksi, we must analytically evaluate the problem. From Malhotra (2), we can use the following equation for elastic properties of steel in the 700- -
900 C (1292-1652 F) range:
_fyt = 0.1 - T*-700 f y20 2000 2
where fyt = yield strength at a specified temperature (ksi) fy20 = yield strength at 20*C (ksi)
T* = specified temperature (*C)
We wish to solve for T* since we know fyt is 0.5 ksi and fy20 is 33.0 ksi. Solving for T* the equation becomes:
T* = 2000 [0.1 - Q + 700
( fy20
= 2000 0.1 - 0.5 ksi + 700
( 33.0ksi)
= 869.7 *C
= 1597*F Therefore, in order for the yield strength of the hanger rod to be reduced to 0.5 ksi, the rod would have to be heated to a temperature of 1597*F. An AISI metallurgist feels that at this temperature and with a maximum load of only 80 lbs., the crystalline structure of the steel would essentially remain unchanged. (3)
The first scenario examined considered a cable fire in cable trays 1, 2, and 5 imediately below the 737' electray hanger. The best avail-able data on free burning cable trays containing Hypalon and EPR jack- '
eted cables appear in the FMRC/EPRI (4) test reports. For these cables, a worst case burning rate of 6.7 kg/ min was measured for an array of 12 cable trays, each 8' long and 18" wide. This reduces to a surface controlled burning rate of 0.1 (lb/ min)/ft2 of cable tray or a heat release rate of 1000 (Btu / min)/ft2 (190 KW/m25 or 16.67 (Btu /
sec)/ft2 assuming a heat of combustion of 10,000 Btu /lb of cable insu- -
lation. Using this burning rate, the cablejtrays under the electray ,
would burn for approximately 53 minutes.
- 3
Cable tray fire test data was examined to establish temperature pro-files above burning cable trays. Tests performed by Sandia Laborator-ies (5) and FMRC/EPRI (4) show that temperatures around 1500 F are reached in the flame region innediately above the surface of a burning cable tray. This temperature drops rapidly with increasing distance above the surface of the cable tray.
The plume temperature profile above the cable fire is dependent on the number of trays in the stack and the width of the trays. The worst case exposure as shown on Attachment A is a fire involving the one 24" .
wide tray and 2-12" wide trays below. Since plume correlations assume a point fire source, a linear fire source such as cable trays must be evaluated as an equivalent point source. This can be done by assuming a fire length of twice the width of the trays as a point source. This yields a plume equivalent to that of a point source with a heat release rate as follows:
Tray 1 2 ft2 Tray 2 2 ft2 Tray 5 8 ft2 12 ft2 h=12ft2 x 16.67 (Btu /sec)/ft2 = 200 Stu/sec H = 4' - Zo, Zo T -l' H = 5' This yields a maximum temperature in the vicinity of the electray sup-port as follows(6):
AT = 300 (K6)2/3 HS /3 where aT = maximum temperature increase above ambient (*F)
K = 1 (when there are no nearby walls)
Q = total heat release rate (Btu /sec)
H = distance above the top of the fuel package (ft.)
4
substituting in the above values:
AT = 300 (200 Btu /sec)2/ 3 = 700*F (5)S/3 T'=' 800*F The second scenario examined is a floor level fire involving transient combustibles below the electray at the 727' elevation. The electray supports are a minimum of 11 feet above the floor. To reach failure temperature would require a fire approaching 4,500 Btu /sec (5 MW).
Using a heat release rate of 290 (Btu /sec)/ft 2 (6), this is equivalent to a 4.4 ft diameter flammable liquid pool fire.
The third scenario examined is a floor level fire involving transient combustibles below the electray at the 737' elevation. The cable tray supports are a minimum of 21 feet above the floor. To reach failure temperature would require an enormous fire of greater than 22,500 Btu /sec (24 MW). This is equivalent to a 10 ft. diameter flammable liquid pool fire. Such a large fire is not considered credible.
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5
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5.0 CONCLUSION
S
- 1) Cable exposure creates a plume temperature around the 737' elec-tray supports (rods) of 800*F. This worst case exposure is approximately 800 F less than the failure temperature of the sup-ports. Therefore, the fire endurance of the electray supports is assured with an adequate margin of safety in the event of a cable fire.
- 2) The plume temperature around the electray rods in case 1 above is 800 F. Therefore, the radiant heat from the fire to the electray .
rods at the 727' elevation will be considerably less than 800 F due to the separation between the electrays.
- 3) The size of a floor level transient fire capable of failing the electray supports at the 727' elevation is 5 MW (4,500 Btu /sec).
This is equivalent to a flammable liquid pool fire of 4.4 ft. in diameter. This transient fire exposure, because of the location and inaccessibility of the area, is not a credible event.
- 4) The size of a floor level transient fire capable of failing the electray supports at the 737' elevation is 24 MW (22,500 Btu /
sec). This is equivalent to a flammable liquid pool fire of 10 I ft. in diameter. This t ransient fire exposure, because of the location and inaccessibility cf the area, is not a credible event.
4 6
6.0 REFERENCES
- 1. Boring, Delbert F., Spence, James C. and Wells, Walter G., " Fire Protection Through Modern Building Codes, Fifth Edition," American Iron and Steel Institute, October, 1981.
- 2. Malhotra, H.L., " Design of Fire-Resisting Structures," Surrey University Press,1982.
- 3. Personal conversation with AISI metallurgist Calvin Cooley.
- 4. FMRC, " Categorization of Cable Flammability, Intermediate Scale Fire Tests of Cable Tray Installations," Electric ' Power Research
, Institute, EPRI NP-1881, August,1982.
- 5. Schmidt, W.H. and Krause, F.R. , " Burn Mode Analysis of Horizontal Cable Tray Fires," SAND 81-0079, NOREG/CR-2431, Sandia National Laboratories, February,1982.
4
- 6. Al pert , Ronald L. and Ward, Edward J., " Evaluating Unsprinklered Fire Hazards," SFPE Technology Report 83-2, 1983.
File Ref: MG-13-010-41 7
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PLAkl Attachment A l
MECHANICAL PIPE CHASE CABLE INFORMATION
- 1. 12", 26', max fill 50 cables
- 2. 12", 27', max fill 56 cables
- 3. 12", 36', max fill 56 cables
- 4. 12", 36', max fill 53 cables 5, 24",13', max fill 104 cables Most typical cables are:
3XJ1261 - 3 conductor 126a. 60 mil PVC 4XJ1261 - 4 conductor 60 mil PVC 12XJ1261 - 12 conductor 80 mil PVC ISPA16G.3 - 1 shielded pan (ie) 2 conductors 2 SPA 16G.3 - 2 shielded pan (ie) 4 conductors
30 mil EPR = 10 lb/1000 LF 15 mil Hypalon = 6 lb/1000 LF 15 mil PVC = 6 lb/1000 LF Each conductor of shield pans 15 mil PVC & 20 mil Hypalon, 30 mil PVC jacket.
Suggest that cables be considered equally distributed among trays.
File Ref: MG-13-010-41 Attachment B1
CABLE INSULATION CALCULATIONS A B C (AB) + C No. of Jacket Insulation Conductors Conductor Insulation (PVC) Total EPR Hypalon 3 10 lbs. 6 lbs. 4 x 6 lbs. 72 lbs.
- 1000 ft. 1000 ft. 1000 ft. 1000 ft.
4 10 lbs. 6 lbs. 4 x 6 lbs. 88 lbs. '
1000 ft.
1000 ft. 1000 ft. 1000 ft.
12 10 l bs . 6 lbs. 5.3 x 6 lbs. 224 lbs.
1000ft. 1000 ft. 1000 ft. 1000 ft.
PVC Hypalon i 2 6 lbs. 1.3 x 6 lbs. 2 x 6 lbs. 40 lbs. '
1000 ft. 1000 ft. 1000 ft. 1000 ft. !
f 4 6 lbs. 1.3 x 6 lbs. 2 x 6 lbs. 68 lbs. l 1000 ft. 1000 ft. 1000 ft. 1000 ft. i TOTAL 492 lbs. '
l 1000 ft.
1 Cables are considered to be equally distributed among trays:
4 492 lbs. + 5 cables = 98.4 lbs.
1000 ft. 1000 ft. - cable
= 0.0984 lbs.
i ft. - cable i
i 2
File Ref: MG-13-010-41 r
Attachment B2 - 1 i
- m. -
CABLE INSULATION CALCULATIONS (CONT'D)
Tray 1: (26 ft.) (50 cables) 0.0984 lbs. = 127.92 lbs, tt.-cable Tray 2: _( 27 ft.) (56 cables) 0.0984 lbs. =
148.78 lbs.
ft.-cable Tray 3: (36 ft.) (56 cables) 0.0984 lbs. =
198.37 lbs.
ft.-cable Tray 4: (36 ft.) (53 cables) 0.0984 lbs. =
187.75 lbs.
ft.-cable Tray 5: (13 ft.) (104 cables) 0.0984 lbs. =
133.04 lbs.
ft.-cable TOTAL 795.86 lbs. cable insulation AREA 0F TRAYS Tray 1: (1 ft.) (26 ft.) = 26 ft2 Tray 2: (1 ft.) (27 ft.) = 27 ft2 Tray 3: (1 ft.) (36 ft.) = 36 ft2 Tray 4: (1 ft.) (36 ft.) = 36 ft2 Tray 5: (2 ft. ) (13 f t. ) = 26 f t2 TOTAL 151 ft2 cable tray surface area Average Tray Loading = 795.86 lbs.
151 ft2
= 5.27 lbs.
ft2 File Ref: MG-13-010-41 Attachment B2 - 2
Temperature, C
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200 400 600 800' 1000 70 60 -
- 400 50 -
.5 - 300
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200 400 600 800 1000 1200 1400 1600 1800 2000 Temperature. F Yield strength of ASTM A36 structural steel at elevated temperatures.
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