ference

NBS

Pubii - cations

oA\

0*4-

\ OS

%

CO NBS TECHNICAL NOTE 923

U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

Applications of Thermography

for Energy Conservation

in Industry

J

7 53

,923

h
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry,

and commerce. The Institute consists of the Office of Measurement Services, the Office of Radiation Measurement and the following Center and divisions:

Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center

for Radiation Research: Nuclear Sciences; Applied Radiation — Laboratory Astrophysics" — Cryogenics 2 — Electromagnetics " — Time and Frequency ". THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard

Reference Materials, the Office of Air and Water Measurement, and the following divisions:

Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Insti- tute consists of the following divisions and Centers: Standards Application and Analysis — Electronic Technology — Center for Consumer

Product Technology: Product Systems Analysis; Product Engineering — Center for Building

Technology: Structures, Materials, and Life Safety; Building Environment; Technical Evaluation and Application — Center for Fire Research: Fire Science; Fire Safety Engineering.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations — Office of International Standards.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted; mailing address Washington. DC. 20234.

- Located at Boulder. Colorado 80302.
tional Bureau of Stantiaias NOV 4 »76

^Applications of Thermography for

bwrz Energy Conservation in Industry

^T^c^i coj M-e, KA , 4 3,3

Charles W. Hurley

Kenneth G. Kreider

Center for Building Technology

Institute for Applied Technology

National Bureau of Standards

Washington, D.C. 20234

^T °

F

Co,

^AU Of *

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Edward O. Vetter, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

(J .$ . NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

Issued October 1976
National Bureau of Standards Technical Note 923

Nat. Bur. Stand. (U.S.), Tech. Note 923, 31 pages (Oct. 1976) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402

(Order by SD Catalog No. CI 3.46:923). Stock No. 003-003- Price 75 cents (Add 25 percent additional for other than U.S. mailing).
APPLICATIONS OF THERMOGRAPHY FOR ENERGY CONSERVATION

IN INDUSTRY

C.Wi Hurley and K.G. Kreider

Infrared thermography has been developed as a tool to measure the

temperature of various types of surfaces. Notable applications include

thermal detection of diseases such as cancer and circulatory problems

in human beings, aerial land mapping of hot surfaces to detect thermal

pollution and geological formations, and remote scanning of buildings

to detect heat losses. More recently, infrared scanning has been used

to detect defects in high amperage electrical connections, transformers,

and steel processing furnaces in industrial environments.

It was the intent of the NBS IR program to build on these

technologies to assist energy conservation engineers to assess heat

losses in industrial plants. IR teams from the NBS Center for Building

Technology had previously used the equipment to survey heat losses in

buildings where the IR camera was found to be particularly useful in

detecting infiltration problems, missing insulation, and construction

defects. Our intent in this project was to survey furnaces and heating

systems in addition to electrical and mechanical systems to find areas suggesting energy conserving actions. This qualitative survey has been

found to be an excellent method to detect heat losses in unit process

equipment and auxiliary systems. This survey method described in this

paper was carried out in fifteen industrial plants in order to develop

a methodology and examine the feasibility of the approach.

In addition to the qualitative survey quantitative data was gathered by calibrating the temperature of the "hot spots" uncovered in

the survey. This information was yery useful in developing priorities

and estimating the magnitude of the heat loss due to a given defect.

Key words: Energy conservation; energy surveys; infrared;

non-destructive evaluation; thermographic surveys; thermography
Introduction

Thermography has been developed as a tool to measure the temperature of various types of surfaces. Notable applications include thermal

detection of diseases such as cancer and circulatory problems in human

beings, aerial land mapping of hot surfaces to detect thermal pollution

and geological formations, and remote scanning of buildings to detect

heat losses. More recently, infrared scanning has been used to detect

defects in high amperage electrical connections, transformers, and

steel processing furnaces. These techniques were reported in an ASTM "Symposium in Thermal Imaging""' by several groups active in the

field. A review of "Thermal Infrared Scanning Capabilities" has been

made by Adler and Loew.2

It is the intent of the NBS IR (Infrared) Program to build on these

technologies to assist energy conservation engineers to assess heat

losses in industrial plants. IR survey teams from the NBS Center for

Building Technology (CBT) had previously used the equipment to survey

heat losses in buildings. It has been found by the CBT studies that the

IR camera is particularly useful in detecting infiltration problems,

missing insulation, and construction defects in a similar way to that

developed by Pettersson and Pal jak .^ The intent in this project was to

survey heating systems in industrial plants in addition to the electrical and mechanical systems to find areas suggesting energy conserving

actions. This qualitative survey has been found to be an excellent

method to detect environmental heat losses in process equipment and

auxiliary systems. The survey described in this report was carried

out in 16 industrial plants in order to develop a methodology and

examine the feasibility of the approach. These plants included tire

manufacturing, cement plants, a copper refinery, forging plants,

foundries, refractory and facing brick plants and heavy equipment

manufacturing.

In addition to the qualitative survey, quantitative data was gathered by calibrating the temperature of the "hot spots" uncovered

in the survey. These "hot spots" result from problems in the basic

insulation design, flaws in the insulation and maintenance errors. However, many "hot spots" indicated malfunctions in the equipment such

as leaking valves, leaking electrical components, failures in materials

and components in invisible areas of the equipment, overheated bearings,

etc. This information was very useful in developing priorities and

estimating the magnitude of the heat loss due to a given defect. This

approach applies the standard calibration methodology developed by

equipment manufacturers for quantitative determinations of surface

temperatures. Examples of this approach are featured in this report.
A third technique has been explored with high energy consuming

equipment such as furnaces. Here, the IR scan was used to survey the

entire radiating surface of a furnace. Thermal mapping was combined

with area measurements to determine total radiation heat losses. This

information was then used as input data for a heat balance on the

furnace. One experiment has indicated that approximately 30% of the

heat consumed by the furnace is being lost from the surfaces by

radiation. Further work is planned in this area to develop the method

and will be reported in a later publication.

Fundamentals of Thermography

Thermography can be defined as a technique of portraying an object using the thermal energy radiating from the surface of the

object. The instrumentation consists of an IR camera and one or more monitors to display the area being scanned. The major difference

between closed circuit television (CCTV) and thermography is that the

thermographic camera scans an area for invisible infrared radiation

and not for visible light. A schematic diagram of the typical thermographic system is shown in Figure 1. The area of interest is scanned

through a special optical lens which will transmit the long-wave IR

signals. The scanning is accomplished by rotating reflecting or refracting prisms and/or oscillating IR reflecting surfaces which

project minute portions of the area being scanned on an IR detector.

A review "Infrared Detectors in Remote Sensing" was presented by

Levinstein and Mudar.4 The IR detector is maintained at a low temperature

-196°C (-321°F) by liquid nitrogen to increase its sensitivity and

stability. The scanning mechanism makes horizontal sweeps across the

surface being scanned. The lines are progressively stepped down to cover the entire surface. The scanning mechanism moves very rapidly

making as many as 25 complete frames each second. Each frame consists

of from 100 to 525 horizontal scan lines depending upon the design

of the system.

The signals from the IR detector are amplified and transmitted to

the monitor where they are further processed to produce visible light

on the surface of a cathode ray tube (CRT).

The intensity of the light on the screen of the monitor is

representative of the magnitude of the invisible IR signal being

projected at that instant on the IR detector. The horizontal and

vertical sweeping of the electron beam in the CRT are synchronized

with the scanning mechanism in the IR camera. Thus, real-time, visible

images of the area being scanned by the IR camera are projected on the screen of the monitor. The image on the screen is photographed to

record the thermal image in the form of a thermogram.
SCHEMATIC DIAGRAM OF THERMOGRAPHIC SYSTEM

PREAMPLIFIER

VIDEO SIGNAL

SIGNAL

PROCESSOR

MONITOR

THERMOGRAPHIC CAMERA

DEWAR

LIQUID NITROGEN

R DETECTOR SCANNING MECHANISM

LENS

f

AREA

BEING

SCANNED

SCANNING SYNCHRONIZING

CONTROLS

MONITOR

THERMAL IMAGE OF AREA

BEING SCANNED

Figure 1
Figure 2

5
Monitors are also used which display the thermal image of the area being scanned by the camera in eight or ten different colors. The

different colors approximately represent different temperature ranges.

Profile monitors are also available which produce a contour presentation of the thermal display or a temperature profile across any selected

horizontal scanning line in the thermal image. Temperature is

displayed as a vertical displacement on the line. A photograph of

the thermographic equipment used in the survey by the NBS IR team

is shown in Figure 2.

The energy losses by thermal radiation from the surfaces of

industrial processing equipment are frequently neglected. These

losses exceed the losses by natural convection at temperatures above

the 150°F - 200°F (65°C - 95°C) range. At temperatures above 600°F

(315°C), the heat losses by thermal radiation are yery high and

losses by convection can usually be neglected.

Thermal radiation exhibits all of the physical characteristics

of light in that it is propagated in straight lines; it can be

reflected, refracted, polarized; and it can exhibit interference

patterns. Since visible light and thermal radiation consist of

electromagnetic waves, the major difference is the wavelength. As

shown in Figure 3, solid bodies emit different levels of thermal

radiation of varying wavelengths depending upon their temperatures.

As the temperature of the body is increased, energy is radiated

at a much higher rate, and at shorter wavelengths. Further increases

in temperature lead to the emission of red light, which is joined by

the yellow, green, blue and violet components in the visible band.

An ingot of iron heated to 1800°F (982°C) would have a bright orange

appearance. However, only about 65 millionths of the energy radiated

by the ingot would fall within the visible band.

Figure 3 illustrates the relative radiated energy for "blackbodies" at various temperatures. A blackbody absorbs all thermal

radiation striking it. A blackbody is also a perfect radiator. The

Stefan-Boltzmann law states that the amount of radiation emitted from

a blackbody per unit time is proportional to the fourth power of the

absolute temperature. A blackbody is a limiting case which is never quite reached by an actual body. An actual body, such as a solid or liquid, radiates less than a similar blackbody at the same temperature.

Therefore, it is necessary to introduce a factor corresponding to the

actual emission of radiant energy from the surface of a solid or liquid divided by the emission from a similar blackbody. This factor

is called the emissivity and is often designated by the symbol "e".

Also the hot object being considered is surrounded by environment

which also radiates according to the Stefan-Boltzmann law. To allow

for these various effects, the Stefan-Boltzmann law may be expanded

to the following expressions:
ENERGY DISTRIBUTION FOR BLACKBODIES AT VARIOUS TEMPERATURES

4 5 6 7 8 9 10 WAVELENGTH (MICROMETERS - m )

Fig-are 3 Energy Distribution for a Black Body

at Various Temperatures

7
ENERGY LOSSES BY RADIATION

(SURROUNDING SURFACES, 60°F (15.6°C)

CO

>-CD

<DC

200°F 600°F

i i 200°C 400°C

1000°F 1400°F

800°C

1800°F

i 1000°C

2200°F

i 600°C 1200°C

TEMPERATURE OF RADIATING SURFACE

2600°F

1400°C

3000°F

Figure 4. Energy Losses By Radiation

(Surrounding Surfaces, 60°F (15.6°C)

8
JB ft

2 -hr

or ^ Watts

h —9

w

171

= 5.67em

(tot)

100

The factors .171 and 5.67 are the Stefan-Boltzmann constants for the

respective equations, ei is the emissivity of the radiating body. T^

is the absolute temperature of the emitting body and T2 is the absolute

temperature of surrounding bodies. The T values in the first equation

are in degrees Rankine which are equal to the temperature on the

Fahrenheit scale plus 459.69, and, in the second equation, the T values

are in kelvins which are equal to the temperature on the Celsius scale

plus 273.15.

In observing the curves in Figure 3, it will also become apparent

that many materials used in industrial processes will absorb thermal

radiation in one wavelength band and re-emit in another wavelength

band. For example, metals being elevated in temperature by high

temperature sources, such as steel under an impinging flame in a slot

furnace, will absorb thermal radiation at the shorter wavelengths and,

when they are allowed to cool in under typical ambient conditions,

the metals will emit at longer wavelengths.

Figure 3 also illustrates the visible wavelength band and the wavelength band of thermographic equipment using the indium antimonide

(In Sb) infrared detector. Although other high speed IR detectors are commercially available which allow the area to be scanned within a different wavelength interval, the limits of their sensitive

band do not lend themselves to the typical elevated temperatures in

the industrial field. For example, the human body radiates at

approximately 310°K. At this temperature only about 2.4% of the total

energy radiating from the body would fall within the InSb band.

Thermography is often confused with infrared photography. The

maximum sensitive wavelength for commercially available infrared

photographic film falls between .8 and .9 micrometers. By observing the

energy distribution curves shown in Figure 3, it will be noted that

surfaces radiating thermal energy in these shorter wavelengths are yery

hot and other heat sensing equipment such as optical pyrometer can

be used. Infrared photography is generally used to display reflections

from the sun, a tungsten filament, or other very hot object. Reflections of this type and reflections from objects at still lower temperature often hinder in obtaining thermograms of industrial surfaces of

interest.
Figure 4 illustrates the energy lost per unit area of a radiating

surface which has an emissivity of unity when the temperature of the

surrounding surfaces is 60°F (15.6°C). The emissivity factors of

typical materials found in an industrial plant at elevated temperatures

are given in Table 1. The energy lost per unit area by thermal radiation can be estimated from the graph of Figure 4 by multiplying the

energy values shown for the various surface temperatures by the

emissivity factor of the surface. It will be noted that the emissivity

factors for typical radiating surfaces do not drastically reduce the

losses shown for surfaces with an emissivity of unity. If the temperatures of surrounding surfaces vary greatly from the 60°F (15.6°C)

value used in plotting the chart shown on Figure 4, and more exact

values are desired, it may be necessary to replot the chart using the

radiation exchange equations and inserting the actual values for the

existing conditions.

Performing Thermographic Surveys in Industrial Plants

In performing the IR thermography surveys certain general

procedures were followed. Equipment operation itself is well prescribed by the manufacturers but many other factors were important to

obtaining useful results.

First, the opportunities for uncovering thermal loss problems in

the plant were discussed with the management, engineering and operation

personnel. Examples of past studies were reviewed to familiarize all

concerned with the intent of the survey. It was found useful to

discuss plant operations and equipment with special emphasis on energy fluxes within the plant.

A "walk-through" with plant personnel was found useful in

selecting targets for scanning. Items such as furnaces, kilns, ovens,

boilers, hot conveyors, flues, bearings, electrical junctions and

transformers, and other hot spots were noted and special operation or maintenance problems were discussed. The IR cameras were then set up

and the equipment calibrated with reference temperature surface

measurements. Conventional photography in the visible spectrum was used in conjunction with the IR thermography for identification of the

location of the thermal information. Emphasis was placed on setting

the hot spot of the field at the top of the temperature range with

the full range selected to include dark areas which could be neglected

due to low thermal output. Optimal range and scale selection requires

considerable skill and multiple ranges were often chosen.

10
The identification of the hot spots and their causes was generally

accomplished during the scanning operation. The use of the color

monitors with on site operating personnel was extremely useful in the

interpretation and analysis of the results. Also, this energy-relevant

information was particularly useful to the plant operating personnel.

Although thermography has many advantages, some of the limitations

were recognized during the surveys. A thermogram of the surface of

any object will indicate only the relative temperatures of each area. The temperature of a reference area within the surface in the thermogram is necessary to obtain quantitative readings. Further, the

emissivities of the surface used as a reference and the surface of

interest must be known. In general, a surface is available within the area being scanned that is suitable for a reference source. However,

the temperatures of the reference surface and the surface of interest

must be within the "gray scale" of the thermogram; i.e., if either

surface is in the black or the saturated white areas of the scale,

quantitative temperature readings cannot be obtained. This limitation

is only objectionable when the range of temperatures of the object in

the thermogram is very large.

Reflections from other equipment, lights, the sun, etc., can limit the use of thermography on equipment with IR reflective surfaces.

Examples include food processing plants and breweries. A typical

example of such reflections from adjacent equipment was experienced

during the NBS survey while observing the limited radiation losses

from a well insulated steel tempering oven. An electrical junction

box about two meters from the oven appeared to be very hot and

electrical problems were immediately suspected. However, when the

junction box was examined, it was found at ambient temperature. It was also found to be a new, clean, zinc covered junction box. Table 1,

indicates an emissivity of .23 is typical for such surfaces which

means that 77% of the thermal radiation striking the box is reflected.

The artifact was easily blocked out of the thermogram by shielding

the box from the radiation from another oven. The surfaces of interest

in the vast majority of industrial plants do not exhibit this reflection

characteristic.

Glass exhibits several unique characteristics that must be considered

in thermography. From Table 1, it will be noted that glass has a relatively high emissivity, 0.85 to 0.95. Also, the transmission of

infrared radiation through glass is high for wavelengths less than 3

micrometers, and drops off rapidly with increasing wavelengths. Glass

is completely opaque for wavelengths greater than 4.5 micrometers.

In observing the sensitive band pass for the InSb detector shown in

Figure 2, it becomes obvious that transmission must be considered if

a radiating surface behind the glass is very hot and if the surface

is being observed by the thermographic camera through the glass.

Solar reflections from glass and other surfaces must also be considered

in thermography. These reflections hinder measurements at wavelengths

less than 3.5 micrometers. Filters are available to eliminate problems

from solar reflections. To eliminate the thermal radiation transmitted

11
through glass filters are available which allow only the radiation

from the surface of the glass to reach the IR sensing element. The

unique infrared characteristics of glass must be considered when it

is one of the materials being scanned.

Plastics such as polyethylene also exhibit unique characteristics

Although these materials are almost completely transparent in the band

pass of the InSb detector, there is a narrow^ absorption peak which

occurs at a wavelength of 3.43 micrometers. If the plastic is the

surface of interest, again, a narrow band pass filter will be required,

Results of NBS Industrial Thermographic Surveys

Several hundred thermograms were accumulated during the industrial

surveys made by the NBS teams. A limited series of thermograms are presented to demonstrate some of the typical applications of thermography in the industrial field.

Tunnel kilns and other continuous processing equipment present

excellent examples of industrial processes which require a complete

shut down of the operation before an inspection can be made for a suspected fault causing defects in the product being produced.

Figure 5 is a photograph of the side of a section at the output end

of a relatively small tunnel kiln used to fire building bricks.

Although the outer structure of the kiln did not indicate any

irregularities, the operator had found it necessary to modify the

cooling section of the kiln to prevent the product from fracturing due

to cooling too rapidly.

Figure 6 is a thermogram of the section shown in Figure 5. The

thermogram shows one of several sections of the sides^at the output

end of the kiln indicating areas where the refractory material lining

the inside of the kiln had fallen. Thermographic scanning of this

kiln gave the plant manager immediate information on problems

concerning the continually increasing fuel consumption of the kiln and

the extremely large percentage of the brick that had to be discarded

because of thermal fracture. The plant engineer closed the kiln, made

the necessary liner repairs, and the kiln was found to work properly

after the repair.

Figure 7 is a photograph of a small section of a large tunnel

kiln that had been repaired. However, the refractory brick that was

used to repair the opening was of a different type from that

originally used and was inferior in insulating properties. Figure 8

is a thermograph of the repaired area and indicates the heat losses

through the repair brick.

12
Figure 5. Outer wall of the exit

of a small tunnel kiln used to fire

building brick. Inner walls and

ceiling constructed of refractory

brick.

Figure 6. Thermogram, light

areas indicated elevated

surface temperature of the

outer structure caused by

failure of the inner

refractory brick.

Figure 7. Portion of the burner

section of a large tunnel kiln.

The refractory brick around the

burners had been removed for

burner modification.

Figure 8. Thermogram, note

the excessive radiation from

the outer structure of brick

caused by conduction from the

improper refractory brick used

to replace the brick around

the burner

13
Figure 9 is a photograph of a section of a much smaller tunnel

kiln used to fire individual sections of high temperatures refractories.

In this section of this kiln, the inside temperatures exceed 3000°

(1650°C) and the walls, ceiling and floor are heavily insulated.

This photograph shows the plumbing for the gas and preheated air for

the burners in this section. Figure 10 is a thermogram of this same section of the kiln showing excessive thermal radiation in the areas

of the burners and areas where the insulation is inadequate or failing.

The temperature of the larger area showing excessive radiation in the

upper left hand section is approximately 450°F (230°C). Another

section of this same kiln is shown in the photograph in Figure 11.

The offset in the outside wall represents an increase in the thickness

of the insulation to reduce the losses from the hotter section of the

kiln. The section at the right hand side of the photograph is the

input section of the kiln. Figure 12 is a thermogram of this section

of the kiln indicating a refractory failure in the upper portion of

this offset. It should be noted that internal failures of this type

can be recorded only by scanning the entire surface of the kiln with

the thermographic camera.

A photograph of a typical process steam boiler found in industry

is shown in Figure 13. This is one of many process steam boilers

originally designed for burning coal but modified to burn oil or

natural gas. A thermogram of this view of the boiler is shown in

Figure 14. Although the side of the boiler is well insulated, the bonnet

is radiating at approximately 450°F (230°C) and the uninsulated sections

of the valves were found to be.320°F (160°C). When compared with many

types of energy consuming equipment in the industrial field, process

steam boilers, in general, operate at relatively high efficiencies.

However, when large areas are observed radiating at higher temperatures

such as the boiler bonnet in this example, and the temperature of the

flue gas was measured at 585°F (310°C), there is always room for

improvement.

Figure 15 is a photograph of a typical indirect heating oven used

in many industrial processing applications. The section shown in this

photograph is the area of the oven where the heat exchanger is located.

A thermogram of this same area shown in Figure 16, indicates good

insulation between the heat exchanger and the panels of the outer

shell. However, the "thermal bridges" formed by the sections of the

outer panels for retention can be observed. The areas around the

maintenance door were found to be 320°F (160°C) with a thermocouple. The

gas burner mounted on the fire box on top of the oven can be observed

at the top of the ladder in the photograph. The radiation from the

outer portion of the burner is shown by the saturated area in the upper corner of the thermogram.

14
Figure 9. Section of small high

temperature tunnel kiln. This

photograph shows three of the

burners in this section of the

kiln.

Figure 10. Thermogram of the

section of the kiln.

Figure 11. Input section of high

temperature kiln. Note the

electrical box and the thermocouple

fixtures at the offset of the kiln.

Figure 12. Thermogram. The

internal refractory brick had

fallen in portions of this

section of the kiln.

15
Figure 13. Process steam boiler.

Steam drum is shown at the top of

the photograph. Exhaust bonnet is

shown in the upper left corner of

the photograph.

Figure 14. The bonnet and the

uninsulated portions of the

valve indicate elevated

temperatures.

Figure 15. Typical oven used to

elevate the temperature of

products by indirect heating.

Note the single burner in the

heat exchanger on top of the oven.

Figure 16. Elevated

temperatures are noted in the area of the burner and around

the maintenance door.

16
Figure 17 is the door of a car bottom furnace in operation. This

furnace is approximately 8 feet, (2.5 m) high, 13 feet (4 m) wide

and 19 feet (5.8 m) deep, and is considered a small to medium size

furnace in the steel industry. The door on the furnace shown in

Figure 17 is not attached to the car as in the typical design of this

type furnace. The door is elevated to remove the flat car. A thermogram of this door is shown in Figure 18. At the time this thermogram

was recorded, the furnace had already heated steel billets on the car

to 2300°F (1250°C) and was operating to retain the billets at that

temperature. The hot gases indicated by the saturated area on the

thermogram at the top and bottom of the door indicate inadequate

sealing in these areas. The surface of the door was measured at

470°F (243°C). The temperature of the cross bracing was 270°F (100°C).

Figures 19 and 20 are thermograms of the doors of large car bottom furnaces where the door was integral with the car. These

furnaces were retaining the temperature of large steel billets at

2300°F (1260°C). Although these furnaces were identical in size

and design, the furnace in Figure 20 had just been rebuilt and the

furnace in Figure 19 was scheduled to be rebuilt in the near future.

The failure of some of the refractory materials is evident in Figure 19.

However, both thermograms indicate excessive heat losses around the

2 to 5 inch (5 to 13 cm) gap around the door to compensate for the

irregularities in the track on which the car is rolled in and out

of the furnace. Furnaces of this type are generally used for periodic

cycling and the excessive thermal mass reduces the thermal efficiency.

However, the efficiency of such furnaces can be improved by using

flexible high temperature insulative material to seal the doors and

reduce infiltration in other areas; loading the furnaces to full

capacity for each cycle; and, reducing the time between unloading

and reloading. The lower thermal conductivity and the lower density of

ceramic fiber furnace lining materials now available should be

considered in rebuilding furnaces of this type.

The low efficiencies of slot furnaces used in forging shops are often referred to in energy conservation papers. However, the losses

that are caused by improper burner adjustment are often neglected.

Since several of the absorption bands of carbon dioxide and water vapor

are within the sensitive waveband of the InSb detector, the IR camera will indicate radiation from these hot compounds found in

exhaust fumes unless special filters are used. An example of how

thermography can be used to detect improper burner adjustment is

demonstrated on the small two burner commercial slot furnace shown

in Figure 21. This furnace was being used in a small forging shop

to heat a series of small billets placed along the bottom of the furnace

Figure 22 is a thermogram of the area just above the front shield of

the furnace where the exhaust gases escape. The thermogram indicates

excessive hot exhaust gases from the left burner. When the operation

of the furnace was observed from the side of the furnace, the flame

from the left burner was projecting upwards behind the shield and

visible outside of the slot.

17
Figure 17, 18. Door of a car bottom furnace in operation. The steel

billets inside had already been heated to a temperature of 2300°F

(1260°C) in this furnace and, at the time of this photograph, the

furnace was operating to retain the billets at this temperature.

Figure 19. Door of a large car bottom furnace retaining the

temperature of steel billets at

2300°F (1260°C). The upper

section of the door indicates

failure in the refractory material,

18

Figure 20. Door of a large

car bottom furnace identical

to that shown in Figure 18

except this furnace has just

been rebuilt. The radiation

around the door is from the

relatively large clearances

allowed for opening and closing

the furnace.
,.F P"""* 1 1 1

H

2

•|

W

20 i

too

200

500

tooo

j .2 ,4 jfl »

«

Figure 21. Small, two burner

slot furnace used in a small

forge shop. One of the

shielding flaps is open. Note

the two burners at the top

of the furnace.

Figure 22. Top of the

furnace shown in Figure 21.

This thermogram indicates

excessive overflow from the

left burner.

19
Figure 23 is a photograph of an identical type slot furnace in the same forging shop. A thermogram of this furnace is shown in Figure 24.

The radiation from the flame can be observed in the area of the

slot and from the exhaust gases from both burners. The results

of this simple survey in this forging shop allowed the operator to

adjust the burners on both furnaces to bring the impinging flame

back into the slot where the steel billets were being heated. This

survey also convinced the operator and the management that the yery

old philosophy of the eye being the best tool for burner adjustment

was no longer sound and a simple thermocouple instrument was purchased

to check the burners periodically. This action resulted in a 60%

reduction in gas consumption in this shop.

The negative pressures generated in industrial furnaces are often the cause of large heat losses from infiltration. The flue

shown in Figure 25 is attached to a reverberation furnace used to

retain an aluminum alloy in a molten state. A thermogram of this

flue, shown in Figure 26, allowed the temperature of the flue gases

to be measured at 2300°F (1260°C). The temperature of the molten

alloy was less than 1000°F (540°C). The thermogram convinced the plant

management to investigate the equipment. Placing a simple damper

in the flue with an automatic control reduced the fuel consumption

by 55%.

2D
Figure 23. Slot furnace of

the same design as that shown

in Figure 21.

Figure 24. Excessive hot

exhaust gases are indicated

from both burners.

Figure 25. Flue on conventional

reverberatory furnace.

Figure 26. The temperature

of the flue gases were

measured at 1300°F (700°C)

higher than the temperature

of the material being

retained at a molten state in

the furnace.

21
Summary

Thermography is a useful tool for scanning industrial equipment

and processes to detect excess heat losses and malfunctions which

result in temperature changes. The examples given in this paper were

limited to several industrial areas where thermography is directly

applicable. However, the authors feel that many industrial plants

would benefit from the results of a thermographic survey. Applicable

examples include: electrical systems and components; boilers; steam

systems; prime movers; grinders; hot conveyors; flues; bearings;

heat exchanges of all types; heat regenerators; any product being

processed at an elevated or reduced temperature; processing equipment;

plant walls; plant heating systems; etc.

The NBS IR industrial plant survey project has built on the

technology of the IR surveys of buildings developed by Pettersson

and Paljak in Sweden and the NBS experience. The industrial plant

survey was related also to the plant energy survey techniques discussed

in NBS handbook 115 (EPIC) with generous help from the East Ohio

Gas Energy Conservation Group, 14 plants were surveyed in Ohio

including tire, ceramic, forging, and metallurgical plants. Excellent

cooperation by these plants and others where more quantitative surveys were conducted indicated that plant management was eager to make

improvements indicated by the IR information.

It was found that frequently the identification of a high heat

loss was all that was needed to make the engineering decision to

correct a fault in the equipment or operating procedure which would

save energy. With many of these improvements such as better balancing

of the combustors as indicated with the slot furnace (Figure 20) no quantitative information was needed in order to select the corrective

course of action. Other problems such as the addition of the damper

in the flue of the reverberatory furnace involve minor investments

but back-of-the-envelope calculations are all that is necessary to

convince management of the need for the improvement after the IR

picture has illustrated the problem. Some modifications suggested

by the IR survey such as the repair of the failed inner refractory

brick shell of the tunnel kiln are performed in conjunction with

maintenance actions prescribed for reasons other than energy conservation. Here the energy savings is a happy by-product of the use of the IR survey in detecting causes for major processing problems.

The IR survey was found to give excellent background information on heat losses on equipment where immediate action may not be warranted,

but this information particularly when reduced to quantitative measures

of heat losses is important in making future decisions on maintenance,

redesign, repair, retrofitting, and replacement.

22
Recommendations

The initial cost of thermographic equipment has retarded the

use of thermography in the industrial field for over 20 years.

However, the increasing costs and curtailments of fuels have encouraged

the use of thermographic techniques in industry. Rather than buying

the necessary equipment at a cost of approximately $50,000, and

developing an in-house team to perform thermographic surveys, many

plants are finding it preferable to obtain these services from an outside contractor. Numerous organizations have been established

within the past two years which specialize in performing thermographic

surveys in industrial plants. The results of such surveys are usually very helpful in fuel conservation programs. Thermographic

equipment is also leased by some of the leading manufacturers. This

option is often desirable when qualified operating personnel are already available in the plant. Because of the significant information

gain using these surveys the authors highly recommend the use of

IR surveys as a tool in industrial energy conservation programs.

23
Table 1

Normal Total Emissivity of Various Surfaces"

Surface

Metals and their Oxides

Aluminum

Polished

Commercial sheet

Heavily oxidized

Aluminum oxide

Aluminum oxide

Aluminum alloy 7075 cleaned with

toluene, then methanol, repeatedly

heated and cooled

Aluminum alloy 2024 cleaned with

toluene, then methanol, repeatedly

heated and cooled

Brass

Polished

Rolled plate, natural surface....

Dull plate

Oxidized by heating at 1110°F....

Chromium, polished

Copper

Polished

Commercial, scraped shiny, but not

mirrorlike

Plate, heated long time, covered

with thick oxide layer

Plate heated at 1110°F

Inconel

Type X, cleaned with toluene, then

methanol, repeatedly heated and

cooled

Type B, cleaned with toluene, then

methanol, repeatedly heated and

cooled

Iron and Steel Metallic Surfaces

Steel, polished

Iron, polished

Cast iron, polished

Smooth Sheet iron

Emissivity

212

212

200-940

530-930

930-1520

450-900

450-910

100-600

72

120-660

390-1110

100-2000

242

72

77

390-1110

450-1620

450-1620

212

800-1880

392

1650-1900

0.095

0.09

0.20-0.31

0.63-0.42

0.42-0.26

0.22-0.16

0.17-0.15

0.10

0.06

0.22

0.61-0.59

0.08-0.36

0.023

0.072

0.78

0.57

0.55-0.78

0.35-0.55

0.066

0.14-0.38

0.21

0.55-0.60

24
Table 1 (Con't.)

Surface

Type 310, brown splotched, oxidized

from furnace service

Tin, commercial tin-plated sheet

iron

Zinc

Commercial 99.1% pure, polished

Galvanized sheet iron, fairly bright.

Galvanized sheet iron, grey

oxidized

Refractories, Building Materials, Paints

and Miscellaneous

Alumina

Mean grain size 10 microns

Mean grain size 50 microns

Mean grain size 100 microns

Asbestos board

Asbestos paper

Brick

Red, rough, but no gross

irregularities

Building

Fireclay

Magnesite refractory brick

Carbon

Filament

Rough plate

Rough plate

Lampblack, rough deposit

Graphite, pressed, filed surface

Carborundum (87% SiC, density 2.3)...

Concrete tiles.

Enamel, white fused, on iron

Glass, pyrex, lead and soda

Glass, polished plate

Gypsum, 0.02 in. thick, on smooth

or blackened plate

Marble, light grey polished

Oak, planed

25

Emissivity

420-980

212

440-620

82

75

1850-2850

1850-2850

1850-2850

74

100-700

70

1832

1832

1832

1900-2560

212-608

608-932

212-932

480-950

1850-2550

1832

66

500-1000

70

70

72

70

0.90-0.97

0.07-0.08

0.045-0.053

0.23

0.28

0.30-0.18

0.39-0.28

0.50-0.40

0.96

0.93-0.94

0.93

0.45

0.75

0.38

0.526

0.77

.77-0.72

.84-0.78

0.98

0.,92-0.82

0.63

0.90

0,,95-0.85

0.94

0.903

0.93

0.90
Table 1 (Cont.)

Surface

Mild steel, cleaned with toluene,

then ethanol, repeatedly heated

and cooled

Iron and Steel Oxidized Surfaces

Iron plate, completely rusted....

Iron, dark grey surface

Rolled sheet steel

Cast iron, oxidized at 1100°F

Steel, oxidized at 1100°F

Iron oxide

Sheet steel, strong, rough

oxide layer

Sheet steel, dense, shiny oxide

layer

Cast iron, rough, strongly

oxidized

Wrought iron, dull, oxidized

Steel plate, rough

Lead, oxidized at 300°F..

Magnesium oxide

Magnesium oxide

Monel 400 oxidized at 1110°F

Monel K-500, cleaned with

toluene, then ethanol, repeatedly

heated and cooled

Nickel, polished

Nickel plate, oxidized by heating

at 1110°F

Stainless Steels

Polished

Type 301 cleaned with toluene,

then ethanol, repeatedly heated

and cooled

Type 316, cleaned with toluene,

then ethanol, repeatedly

heated and cooled

Type 347, cleaned with toluene,

then ethanol, repeatedly heated

and cooled

Emissivitv

450-1950

67

212

70

390-1110

390-1110

930-2190

75

75

100-480

70-680

100-700

390

530-1520

1650-3100

390-1110

450-1610

212

390-1110

212

450-1740

450-1600

450-1650

0.20-0.32

0.69

0.31

0.66

0.64-0.78

0.79

0.85-0.89

0.80

0.82

0.95

0.94

0.94-0.97

0.63

0.55-0.20

0.20

0.41-0.46

0.46-0.65

0.072

0.37-0.48

0.074

0.57-0.55

0.57-0.66

0.52-0.65

26
Table 1 (Con't)

2 Surface °_F Emlssivity

Paints, Lacquera, Varnished

Snow-white enamel varnish on rough

iron plate 73 0.906

Black shiny lacquer, sprayed on iron 76 0.875

Black matte shellac 170-295 0.91

Black or white lacquer 100-200 . 80-0 .95

Flat black lacquer 100-200 0.96-0.98

Oil paints, 16 different, all colors.. 212 0.92-0.96

Aluminum paints and lacquers, 10%

Al, 22% lacquer body on rough

or smooth surfaces 212 0.52

Aluminum paint with silicone

vehicle, 2 coats on Inconel 500 .29

Other aluminum paints, varying age and

aluminum content 212 0.27-0.67

Aluminum lacquer, varnish binder on rough plate 70 0.39

Aluminum paint, after heating to

620*F 300-600 0.35

Radiator paint, white, cream,

bleach 212 0.79,0.77,0.84

Radiator paint, bronze 212 0.51

Lacquer coatings, clear, 0.001-0.015

in. thick on aluminum alloys 100-300 0.87-0.97

Claar silicone vehicle coatings

0.001-0.015 in. thick on mild

steel 500 0.66

Plaater, rough lime 50-190 0.91

Porcelain, glazed 72 0.92

Quartz, rough, fused 70 0.93

Roofing paper 69 0.91

Rubber, hard, glossy plate 74 0.94

Rubber, soft, grey, rough, (reclaimed)... 76 0.86

Silica, mean grain size 10 microns 1850-2850 0.42-0.33

Silica, grain size 70-600 microns 1850-2850 0.62-0.46

Selected from a compilation by H.C. Hottel, published in Table A. 23 of Heat

Transmission, 3rd Edition, 1954 by W.H. MacAdams, McGraw-Hill Book Co., Inc.

2When temperatures and emissivities appear in pairs separated by dashes, they

correspond, and linear interpolation is possible.

27
References

(1) "Symposium on Thermal Imaging," June 26, 1975, Montreal,

Canada, sponsored by the New Methods Review Subcommittee

ASTM E07.98.

(2) Adler, P. and Loew, M., "Thermal Infrared Scanning

Capabilities, A Survey," Analytic Services, Inc., Falls

Church, Va. (1975).

(3) Pettersson, B. and Paljak, J., "Application of Infrared

Thermography In Buildings," AGA Corp., Stockholm, Sweden.

(4) Levinstein, H. and Mudar, J., "Infrared Detectors in Remote

Sensing," IEEE Proceedings, Jan. 1975.

23
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-9232. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE .APPLICATIONS OF THERMOGRAPHY FOR ENERGY CONSERVATION

IN INDUSTRY

5. Publication Date October 1976

6. Performing Organization Code

7. AUTHOR(S)

C.W. Hurley and K.G. Kreider

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as item 9

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) Infrared thermography has been developed as a tool to measure the temperature of various

types of surfaces. Notable applications include thermal detection of diseases such as cancer and circulatory problems in human beings, aerial land mapping of hot surfaces

to detect thermal pollution and geological formations, and remote scanning of buildings

to detect heat losses. More recently, infrared scanning has been used to detect defects

in high amperage electrical connections, transformers, and steel processing furnaces in

industrial environments.

It was the intent of the NBS IR program to build on these technologies to assist energy

conservation engineers to assess heat losses in industrial plants. IR teams from the NBS

Center for Building Technology had previously used the equipment to survey heat losses ih

buildings where the IR camera was found to be particularly useful in detecting infiltration problems, missing insulation, and construction defects. Our intent in this project

was to survey furnaces and heating systems in addition to electrical and mechanical systems

to find areas suggesting energy conserving actions. This qualitative survey has been

found to be an excellent method to detect heat losses in unit process equipment and

auxiliary systems. This survey method described in this paper was carried out in fifteeji

industrial plants in order to develop a methodology and examine the feasibility of the

approach.

In addition to the qualitative survey quantitative data was gathered by calibrating the

temperature of the "hot spots" uncovered in the survey. This information was very useful

-in Hgirplnp-ing prinrifipg anrl PsM'TTiflfing thp magnitude of the heat loss due to a given detect

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Key words: Energy conservation; energy surveys; infrared;

non-destructive evaluation; thermographic surveys; thermography

18. AVAILABILITY LX_ Unlimited

^j For Official Distribution. Do Not Release to NTIS

| y

1 Order From Sup. of Doc, U.S. Government Printing Office Wa:

:r From bup. of Doc, U.i>. Ijovernment Printing Ut

hington, D.C. 20402, SD Cat. No. C13.A6;923

^) Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

31

22. Price $.75

USCOMM-DC 29042-P74

6 U. S. GOVERNMENT PRINTING OFFICE : 1976—240-848/8

NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau

of Standards research and development in physics,

mathematics, and chemistry. It is published in two

sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of physical and chemical research, with major emphasis on

standards of physical measurement, fundamental constants, and properties of matter. Issued six times a year. Annual subscription: Domestic, $17.00; Foreign, $21.25. • Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design, numerical

analysis, theoretical physics and chemistry, logical de- sign and programming of computers and computer sys- tems. Short numerical tables. Issued quarterly. Annual

subscription: Domestic, $9.00; Foreign, $11.25.

DIMENSIONS/NBS (formerly Technical News Bulletin) —This monthly magazine is published to inform

scientists, engineers, businessmen, industry, teachers,

students, and consumers of the latest advances in science and technology, with primary emphasis on the work at NBS. The magazine highlights and reviews

such issues as energy research, fire protection, building

technology, metric conversion, pollution abatement,

health and safety, and consumer product performance.

In addition, it reports the results of Bureau programs

in measurement standards and techniques, properties of matter and materials, engineering standards and services, instrumentation, and automatic data processing.

Annual subscription: Domestic, $9.45; Foreign, $11.85.

NONPERIODICALS

Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

industrial practice (including safety codes) developed

in cooperation with interested industries, professional

organizations, and regulatory bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other

special publications appropriate to this grouping such

as wall charts, pocket cards, and bibliographies.

Applied Mathematics Series—Mathematical tables, manuals, and studies of special interest to physicists, engineers, chemists, biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides

quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a world-wide

program coordinated by NBS. Program under authority

of National Standard Data Act (Public Law 90-396).

NOTE: At present the principal publication outlet for these data is the Journal of Physical and Chemical

Reference Data (JPCRD) published quarterly for NBS

by the American Chemical Society (ACS) and the American Institute of Physics (AIP). Subscriptions, reprints,

and supplements available from ACS, 1155 Sixteenth

St. N.W., Wash. D. C. 20056. Building Science Series—Disseminates technical infor- mation developed at the Bureau on building materials,

components, systems, and whole structures. The series presents research results, test methods, and performance criteria related to the structural and environmental

functions and the durability and safety characteristics

of building elements and systems.

Technical Notes—Studies or reports which are complete

in themselves but restrictive in their treatment of a

subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under proce- dures published by the Department of Commerce in Part

10, Title 15, of the Code of Federal Regulations. The

purpose of the standards is to establish nationally rec- ognized requirements for products, and to provide all concerned interests with a basis for common understanding of the characteristics of the products. NBS

administers this program as a supplement to the activities of the private sector standardizing organizations.

Consumer Information Series—Practical information,

based on NBS research and experience, covering areas

of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's technological marketplace.

Order above NBS publications from: Superintendent

of Documents, Government Printing Office, Washington,

D.C. 20402. Order following NBS publications—NBSIR's and FIPS

from the National Technical Information Services,

Springfield, Va. 22161. Federal Information Processing Standards Publications (FIPS PUBS)—Publications in this series collectively constitute the Federal Information Processing Standards Register. Register serves as the official source of information in the Federal Government regarding stand- ards issued by NBS pursuant to the Federal Property

and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented

by Executive Order 11717 (38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal

Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or final reports on work performed by NBS for

outside sponsors (both government and non-govern- ment). In general, initial distribution is handled by the sponsor; public distribution is by the National Technical Information Services (Springfield, Va. 22161) in paper copy or microfiche form.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey

bibliographies are issued periodically by the Bureau:

Cryogenic Data Center Current Awareness Service. A

literature survey issued biweekly. Annual subscription: Domestic, $20.00; Foreign, $25.00.

Liquified Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00.

Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription: $20.00.

Send subscription orders and remittances for the pre- ceding bibliographic services to National Bureau of Standards, Cryogenic Data Center (275.02) Boulder,

Colorado 80302.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington, D.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use, S300

POSTAGE AND FEES PAIO

U.S. DEPARTMENT OF COMMERCE COM-21S

SPECIAL FOURTH-CLASS RATE BOOK

*?^> YEARS NBS 1301-1976

'^6-l9lfe