NATIONAL BUREAU OF STANDARDS REPORT

10 138

FAILURE OF HYGROTHERMOMETER THERMAL SHIELD

TOP MOUNTING PLATE

for

U. S. Department of Commerce

Environmental Science Services Administration

Weather Bureau

Silver Spring, Md. 20910

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards ' was established by an act of Congress March 3, 1901. Today,

in addition to serving as the Nation’s central measurement laboratory, the Bureau is a principal

focal point in the Federal Government for assuring maximum application of the physical and

engineering sciences to the advancement of technology in industry and commerce. To this end

the Bureau conducts research and provides central national services in four broad program

areas. These are: (1) basic measurements and standards, (2) materials measurements and

standards, (3) technological measurements and standards, and (4) transfer of technology.

The Bureau comprises the Institute for Basic Standards, the Institute for Materials Research, the

Institute for Applied Technology, the Center for Radiation Research, the Center 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 an Office of Measurement Services and the following technical

divisions:Applied Mathematics—Electricity—Metrology—Mechanics—Heat—Atomic and Molecular Physics—Radio Physics -—Radio Engineering -—Time and Frequency -—Astrophysics -—Cryogenics.

THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to im- proved methods of measurement standards, and data on the properties of well-characterized

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

produces, and distributes standard reference materials; relates the physical and chemical properties of materials to their behavior and their interaction with their environments; and provides

advisory and research services to other Government agencies. The Institute consists of an Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—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 in the development of technological

standards, and test methodologies; and provides advisory and research services for Federal, state, and local government agencies. The Institute consists of the following technical divisions and

offices: Engineering Standards—Weights and Measures — Invention and Innovation — Vehicle Systems Research—Product Evaluation—Building Research—Instrument Shops—Measurement Engineering—Electronic Technology—Technical Analysis.

THE CENTER FOR RADIATION RESEARCH engages in research, measurement, and application of radiation to the solution of Bureau mission problems and the problems of other agencies and institutions. The Center consists of the following divisions: Reactor Radiation—Linac Radiation—Nuclear Radiation—Applied Radiation. THE CENTER FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and

provides technical services designed to aid Government agencies in the selection, acquisition, and effective use of automatic data processing equipment; and serves as the principal focus

for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center consists of the following offices and divisions: Information Processing Standards—Computer Information — Computer Services — Sys- tems Development—Information Processing 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 Measure- ment System, and 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—Clearinghouse for Federal Scientific and Technical Information ' —Office of Technical Information and Publications—Library—Office of Public Information—Office of International Relations.

' HcadquKrt«r8 and LabniatorieH nt GaithorMburR. Maryland, unteas otherwitic noted; niaUinR addrcas Washington. D.C. 20234.

^ Located at Boulder. Colorado 80302.

^ Located at 6285 Port Royal Road. SprinKficld. VirRinia 22161.
NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT

SnOSS'fc December 18, 1969

NBS REPORT

10 138

FAILURE OF HYGROTHERMOMETER THERMAL SHIELD

TOP MOUNTING PLATE

by

G. M. Ugiansky

for

U. S. Department of Commerce

Environmental Science Services Administration

Weather Bureau

Si Iver Spring, Md. 20910

IMPORTANT NOTICE NATIONAL BUREAU 01

for use within the Governm

and review. For this reaso whole or in part, is not a Bureau of Standards, Wast

the Report has been speciti

Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

regress accounting documents intended

it IS subjected to additional evaluation

ature listing of this Report, either in

n the Office of the Director, National

ver, by the Government agency tor which

nal copies for its own use.

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

An Hygrothermometer Thermal Shield Top Mounting Base v/as received

after removal from ET-WBO-Montgomery , Alabama. Examination of the

mounting base determined that the failure was by exfoliation corrosion.

A photograph of the cross-section of one of the affected areas is

shown in Figure 1. Exfoliation is a type of corrosion that progresses

approximately parallel to the outer surface of the metal, causing layers

of the metal to be elevated by the formation of corrosion products. The

alloy of which the mounting base was constructed (2024-T4) is known to b

susceptible to exfoliation corrosion in the atmosphere. Failure of some

but not all of the top mounting bases in use is most likely caused by

variations in heat treatment of these parts. Variations in heat treatment of 2024 can cause drastic changes in its exfoliation resistance.

In general, 2024 is not recommended for resistance to exfoliation.

The solution to this problem, is to replace the 2C24-T4 with an

alloy which is resistant to exfoliation. An alloy which meets the

Is

desired corrosion resistance properties^

5052-0. This alloy is

very resistant to exfoliation, but has lower mechanical properties

than the 2024-T4. Alloy 5052-0 has a nominal ultimate tensile

strength of 28,000 psi and yield strength of 13,000 psi. Since high

mechanical strength is not necessary in the construction of the thermal

shield, this alloy should be acceptable.

I

Figure 1. Cross-section of exfoliated 2024-T4

Aluminum Alloy hygrothermometer thermal

shield top mounting plate. X 2

k

It is, therefore, recommended that the material for construction

of the top mounting base be changed to 5052-0 aluminum alloy. It is

further recommended that all other parts constructed of wrought alloys

also be replaced by 5052-0 in future assemblies. This is especially

important for the 2024-T4 mounting plates. The cast parts should be

satisfactory as specified in the specifications drawings.

It is also suggested that any brass fasteners be replaced by

fasteners less likely to cause galvanic corrosion. Acceptable alternatives are, in order of decreasing desirability: chromium plated,

zinc plated (i.e., galvanized), or cadmium plated fasteners.

The above modifications in the design of the thermal shield,

along with the anodization process already in use, should correct

the exfoliation problem encountered with the top mounting base and

prevent future problems with other components of the assembly.

USCOMM-NHS-DC

2


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