reau of Standards
The progcram of research on building materials and structures, carried on by the

National Bureau of Standards, was undertaken with the assistance of the Central Housing Conunittee, an informal organization of governmental agencies concerned with

housing construction and finance, which is cooperating in the investigations through a committee of principal technicians.

CENTKAL HOUSING COMMITTEE

ON RESEARCH, DESIGN, AND CONSTRUCTION

A. C. Shire, Chairman, Howard P. Vermilya, Vice Chairman,

United States Housing Authority. Federal Housing Administration.

Sterling R. March, Secretary.

Pierre Blottke,

Federal Home Loan Bank Board.

Hugh L. Dryden,

National Bureau of Standards.

Louis A. Simon,

Public Buildings Administration.

Luther M. Leisenring,

Construction Division (War).

Edward A. Poynton,

Office of Indian Affairs.

John S. Donovan,

Farm Security Administration.

George W. Trayer,

Forest Service (F. P. Laboratory).

Joseph M. DallaValle,

Public Health Service.

George E. Knox,

Yards and Docks (Navy).

William R. Talbott,

Veterans' Administration.

Wallace Ashby,

Bureau of Agricultural Chem-istry and Engineering.

NATIONAL BUREAU OF STANDARDS

STAFF COMMITTEE ON ADMINISTRATION AND COORDINATION

Hugh L. Dryden, Chairman,

Mechanics and Soimd.

Phaon H. Bates, Gustav E. F. Lundell,

Clay and Silicate Products. Chemistry.

HoBART C. Dickinson, Addams S, McAliister,

Heat and Power. Codes and Specifications.

Warren E. Emley, Henry S. Rawdon,

Organic and Fibrous Materials. Metallm-gy.

The Forest Products Laboratory of the Forest Service is cooperating with both

committees on investigations of wood constructions.

[For list of BMS publications and directions for purchasing, see cover page iii]
UNITED STATES DEPARTMENT OF COMMERCE • Harry L. Hopkins, Secretary

NATIONAL BUREAU OF STANDARDS • Lyman J. Briggs, Director BUILDING MATERIALS

and STRUCTURES

REPORT BMS58

Strength of Soft-Soldered Joints in Copper Tubing

by

ARTHUR R. MAUPIN and WILLIAM H. SWANGER

ISSUED SEPTEMBER 20,1 940

The National Bureau of Standards is a fact-finding organization;

it does not "approve" any particular material or method of construction. The technical findings in this series of reports are to be construed accordingly.

UNITED STATES GOVERNMENT PRINTING OFFICE • WASHINGTON • I94O

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, WASHINGTON, D. C. • PRICE lO CENTS
Foreword

This paper gives the results of an investigation of the strengtli of sleeve joints in

copper water tubing with wrought-copper and cast-brass couplings soldered with

(50-50) tin-lead and (95-5) tin-antimony alloys. The increasing use of thin-walled

copper tubing with soft-soldered sleeve joints in domestic plumbing installations and

the need for definite information on temperature limitations and the effects of longtime loading on the strength of such joints prompted the investigation, begun in 1936

in cooperation with the Federal Housing Administration. Since 1937 the investigation

has been continued on the Research Associate Plan, under the sponsorship of the Copper

and Brass Research Association and Committee A40, of the American Standards Association.

In the proposed American Standard for Soldered-Joint Fittings, the pressure ratings were based upon the results of the strength tests described in this paper. Results of

similar tests on joints made with other less commonly used soft solders will be given in

another paper.

Lyman J. Briggs, Director.

[n]
Strength of Soft-Soldered Joints in Copper Tubing

6?/ ARTHUR R. MAUPIN and WILLIAM H. SWANGER

CONTENTS

Page Foreword ii

I. Introduction 1 II. Previous investigations 2

III. Scope of investigation 3 IV. Materials 3

1. Tubing 3

2. Fittings 4

3. Solders and fluxes . 4

V. Short-time tensile tests 4

1. Depth of bore 4

2. Diametral clearance; compositions

of solder and of metals sol- dered 5

(a) Test procedure 5

(b) Discussion of results 6

3. Tests at 0° to 350° F on joints made

with (50-50) tin-lead and with

(95-5) tin-antimonj- solders 9

VI. Joints made with (50-50) tin-lead solder^ 9

1. Long-time tests at room temperature (about 85° F) 10

2. Long-time tests at 85° F on joints

in 3-inch tubing 12

Page VI. Joints made with (50-50) tin-lead solder —Continued.

3. Long-time tests at 123°, 173°, 218°,

and 250° F 12 VII. Maximum shear-stress—temperature re- lations for joints made with (50-50)

tin-lead solder 18 VIII. Maximum internal-pressure—temperature curves for joints in copper tubing made with (50-50) tin-lead solder 19 IX. Joints made with (95-5) tin-antimony

solder 20

1. Long-time tests at room temperature (about 85° F) 20

2. Long-time tests at 250° and 325° F_ 21 X. Maximum shear-stress—temperature re- lations for joints made with (95-5)

tin-antimony solder 22 XI. Fluctuating tensile load tests on joints

made with (50-50) tin-lead solder__ 22 XII. Summary 23 XIIT. Selected references 25

ABSTRACT

An extended investigation was made of the strength,

under tensile loading, of sleeve joints in copper tubing,

with wrought-copper and cast-brass couplings, soldered with (50-50) tin-lead and (95-5) tin-antimony alloys. In short-time tests (speed of movable head 0.06 inch

per minute) the strength of the joints was substantially

equal to that of the tubing or fittings. The strength

varied directly with the depth of insertion of the tubing

into the fitting, and was greater at diametral clearances

of 0.004 to 0.010 inch between tubing and fitting than

at greater clearances. The strengths were higher at 0°F than at 85° F and decreased rapidly as the temperature was further increased. In long-time tests (10,000 hours or more) under

constant tensile loads, the strength of joints soldered with tin-lead was about one-eighteenth of that obtained

in short-time tests, from 85° to 250° F; joints soldered with tin-antimony had from one-fifth to one-seventh

of the short-time strength, depending upon the temperature. At 250° F and upward, diffusion of copper from

the tubing into the solder films, in joints made with tin

! or tin-alloy solders, may weaken or destroy the metallic bond between the solder and tubing. Results of pulsating tensile-load tests, limited to the

joints soldered with (50-50) tin-lead, indicated that

the strength under repeated loading was not less than

under steady loading.

I. INTRODUCTION

For many years the most commonly used

materials for water pipes in buildings were iron

and steel, galvanized or uncoated. Copper

and brass pipes with threaded fittings were

widely used in installations where maximimi

dependability and freedom from interruptions

in service because of corrosion difficulties were

desired. Because of the necessity for threading

the pipe, the wall thiclmesses were the same as those of iron and steel pipes of corresponding

sizes. The greater cost of the metals made

brass and copper piping considerably more

expensive than iron and steel piping.

The excellent resistance of copper to corrosion damage by most municipal water supplies

mad.e the heavy wall thickness of iron-pipe-size

[1]
copper pipe superfluous, and the availability of thin-walled seamless-drawn copper tubing provided a piping material little more expensive

per foot of length than iron and steel pipe of equal capacity. The thin-walled tubing could

not be threaded to fit ordinary threaded pipe

fittings, and various types of compression fit- tings were devised for joining the tubing.

These fittings were expensive and bulky, and

difficult to install properly. Thin-walled copper

tubing was not widely used for domestic plumbing in this country until the introduction, about

1930, of the sleeve-type fittings for soldered

joints. Since that time, the use of thin-walled

copper tubing for water piping has increased

greatly.

Because of the lack of service records over a

sufficiently long time, the strength and permanence of soft-soldered joints in copper tubing were subject to question, and there was need

for definite information on their strength under

conditions occurring in service.

In 1936 the National Bureau of Standards

began a study of the strength of soft-soldered

joints in copper tubing, in cooperation with

the Federal Housing Administration. Since

1937 this study has been, continued under the

Research Associate Plan with sponsorship of the Copper and Brass Research Association and

Committee A40 of the American Standards

Association.

11. PREVIOUS INVESTIGATIONS

Papers giving technical information on the

strength of solders and soldered joints are listed in section XIII. Hereafter references to these

papers are indicated by numbers in brackets.

General information on soft solders, their

compositions, properties, and methods of application, were described by Hiers [1],^ Nightingale [2], and Macnaughtan, Hedges, and

Lewis [3]. Coffman and Parr [7], Dean and Wilson [8], Eyles [9], and Barber [10] discussed fluxes for use with soft solders and theories on the action

of such fluxes. The bonding action between soft solders and

the metals joined by soldering was discussed by

1 Figures in brackets indicate the literature references at the end of this report.

Daniels and Macnaughtan [6] and by Chadwick [12]. A series of articles by Hook [5] described

methods for soldering copper and copper alloys,

including sleeve joints in copper tubing.

Gonser and Heath [4] determined physical

and mechanical pi'operties of tin-lead solders of

dift'crent degrees of purity and compared the

strengths of lap joints in brass strip, made with

the solders they investigated. The strengths

under prolonged loading at room temperature of

tin and tin-lead solders, and of joints in various

metals soldered with tin and tin alloys, were

investigated by Freeman and Quick [11]. A number of papers have been published on

the rapid decrease in strength of tin, lead, and

their alloys, as the temperature is increased

above ordinary room temperatures. One of the

earliest, dealing with soft solders, was published

in 1919 by Hill and Carpenter [13]. Hanson

and Sandford [14] investigated the creep properties of tin and tin alloys; McKeown [15] studied the creep of lead and lead alloys. The

creep of soft solders and of soldered joints was

studied by Baker [16]. In general, the results of these investigations

showed that tin, lead, and tin-lead solder alloys

elongated appreciably when subjected at room

temperature to prolonged tensile loading at

stresses much lower than those reqinred to produce fracture in an ordinary tensile test, and

further, that the rate of elongation increased

rapidly as the temperature was increased.

Similar effects of increased temperature, and

time under load, were observed on soft-soldered

joints, but the strength of the joints could not

be determined by tests on the solder alloys

themselves.

Very few systematic investigations had been

made on the strength of soft- or hard-soldered

joints in copper tubing. Noyes [17], of the

United States Navy Department, studied the

behavior of such joints under different loading

conditions, and temperatures up to 400° F. However, quantitative data were lacking on the

effects of these variables on the strength of soft- soldered joints in thin-walled copper tubing,

under service conditions encountered in domestic plumbing. Available information indicated

that joints made with hard solders (brazing

alloys) maintained adequate strength to tern-

[2]
peratures at which the tubing and fittings

themselves were seriously weakened.

III. SCOPE OF INVESTIGATION

Before planning the program for this investigation, visits were made to the plants of manufacturers of tubing and fittings, and the proposed program was discussed with their technical staffs. In particular, their recommendations were obtained on the methods of making

the joints. Observations were made of the

types of tubing and fittings, and methods of

making the joints, in the plumbing installations

of many houses and apartments in and near Washington.

It was decided to confine the study to copper

tubing and wrought-copper or cast-brass fittings

which were commercially available, and to

joints in straight couplings made by the

methods which presumably were followed by

the plumbers.

The most important factors affecting the

strength and reliability of soldered joints in copper tubing in the variety of service conditions

encountered in domestic plumbing were considered to be the following:

1. Depth of bore in the fitting, that is, the

length of overlap between fitting and tubing,

which, in a properly made joint, is completely

filled with the film of solder.

2. Diametral clearance between tubing and

fitting.

3. Possible difference in strength of joints

with cast-brass and with wrought-copper fittings.

4. Effect of temperatures in the range 85° to 250° F on the strength of soft-soldered joints

made with dift'erent diametral clearances and

solders, under different tensile loads maintained constant over long periods.

5. Effects of corrosion.

6. Effect of low temperature (to 0° F).

7. Efl'ect of vibratory stresses. All the above factors are equally pertinent

to hard-soldered joints, except that the ele- vated temperature eft'ects would be observed

at higher temperatures than with soft-soldered

joints. However, as hard solders or brazing

alloys are not often used in plumbing installations in ordinary housing construction, it was

considered advisable to include in the investigation only soft-soldered joints, and at the outset, joints made with (50-50) tin -lead and

(95-5) tin-antimony solders. It also seemed in- advisable to undertake activities directed to- ward development of new solders, fhixes, or new

types of tubing and fittings.

IV. MATERIALS

1. Tubing

It is obvious that for satisfactory soldering of

sleeve joints the outside diameters of the tubing

and inside diameters of the sleeve fittings must

be held to close tolerances in order to accomplish

satisfactory soldering. Nationally recognized

specifications for thin-walled copper tubing,

such as those of the American Society for Testing Materials ^ and the Federal Specifications

Executive Committee,^ have been in force for a number of years and manufacturers of such

tubing, for use with soldered fittings, apparently

have no difficulty in meeting the rigid requirements for dimensions prescribed in these specifications. Observations on tubing and fittings

from various representative sources have shown

that they are satisfactorily interchangeable.

The type designations, K, L, and M, of these

specifications have become "standard" designations for thin-walled copper water tubing in the

industry. For equal nominal sizes the outside

diameters of all types are the same. In the

smaller sizes used in household plumbing, the

wall thickness of type M (the thinnest) is approximately 70 percent of that of type L,

which, in turn, is about 70 percent of that of type K (the thickest). The wall thickness of "standard" iron pipe is about twice that of type

K, 2K to 3 times that of type L, and nearly 4

times that of type M.

Types K and L are available in the annealed

and in the hard-drawn condition as well as in intermediate tempers, with tensile strength

ranging from about 30,000 pounds per square

inch for the annealed tubing to about 50,000

pounds per square inch for the hard drawn

2 Standard Specifications for Copper Water Tube. ASTM Designation:

B88-39. Am. Soc. Testing Materials, Standards, pt. 1, Metals, p. 640

(1939).

i Federal Specification WW-T-799, Tubing; Copper. Seamless (for use with soldered or flared fittings). Obtainable from Superintendent of Documents, Washington, D. C. Price 5 cents.

[3]
tubing. Type M is available generally only

in the hard-drawn condition.

2. Fittings

Both cast and wrought fittings for soft- soldered joints in thin-walled copper tubing

are available commercially. Cast fittings are made generally from "red brass" (85 percent of

copper, 5 percent of tin, 5 percent of zinc, 5 percent of lead) ; WTought fittings, from copper

of the same composition as the tubing. Most

of the specimens used in this investigation were made with %-inch types K or L tubing

and straight couplings of either wrought copper

or cast brass.

3. Solders and Fluxes

The joints in thin-walled copper tubing for carrying water are most generally made with

soft solders. Tin-lead solders predominate,

the familiar "half-and-half," or 50-percent-tinoO-percent-lead alloy, being the composition

most frequently used. This alloy flows readily

at 420° F, at which temperature hard-drawn

copper tubing is not softened by annealing

during the time required to solder a joint.

During the past few years the composition

95-percent-tin, 5-percent-antimony has come

into the field of soft solders for this type of work. This alloy flows readily at about 465°

F, which also is not sufficiently high to soften

significantly the hard-drawn tubing when the

joints are made.

The alloys, 5 percent tin and 95 percent lead,

molten at about 595° F; 39 percent tin, 1 per- cent antimony, and 60 percent lead, molten at about 430° F; 2.5 and 5 percent silver, re- mainder lead, molten at about 580° and 670° F,

respectively; and 5 percent silver and 95 per- cent cadmium, molten at about 740° F; may

also be included in the class of soft solders. Joints in the three "standard" types of thinwalled copper tubing can be made with "hard"

solders or brazing alloys melting in the range

1,175° to 1,300° F. At these temperatures,

however, the hard-drawn tubing is annealed so that the strength of the tubing in the vicinity of

the joint is practically that of annealed tubing.

The hard solders are used for installations in

which the tubing may be subjected, during

service, to temperatures at which soft solders

would not be reliable. Zinc chloride or mixtures of zinc and am- monium chlorides are used almost exclusively

as fluxes for soft-soldered joints. These fluxes are acid in reaction, but unless needlessly

excessive amounts have been used, no damage

to the joint by corrosion is to be feared. Apparently the most satisfactory form in which

to use the flux for making sleeve-type joints in

tubing is to have the fluxing material incorporated with mineral grease into a paste.

Such preparations are available commercially.

With the hard solders, a flux that is not decomposed at the soldering temperature must be

used. Borax or mixtures of borax and boric

acid are satisfactory.

Soft-soldered joints in copper tubing are made

satisfactorily with gasoline or air-acetylene

torches; hard-soldered joints require the use of an oxy-gas or oxy-acetylene torch, preferably

the latter. No difficulties were encountered in obtaining

properly soldered joints with diametral clear- ances of about 0.004 inch, in which the

solder was uniformly and completely spread

throughout the space designed for it. Many

joints were sectioned to ascertain this fact. In

the tests involving strengths at different clear- ances up to 0.060 inch, special means were used

for filling the joints with diametral clearances more than 0.008 inch.

V. SHORT-TIME TENSILE TESTS

1. Depth of Bore

Joints with depth of bore ranging from to 1 inch, were made with (50-50) tin-lead solder,

%-inch K-hard tubing, and both wroughtcopper and cast-brass couplings. The joints were pulled apart in a screw-driven beam-andpoise tensile testing machine having a capacity

of 10,000 pounds. Before the loads were applied, the speed of the movable head of the

testing machine was adjusted to 0.06 inch per

minute of travel under no load. This speed

setting was used for all of the short-time tensile tests reported in this paper. The results,

plotted in figure 1, showed that the loads to

[4]
rupture the soldered joints increased in an

approximately direct proportion to the in- crease in depth of bore in the fitting, in both

types of fitting. It was observed also that all of the commercial fittings for types K, L, and M tubing are designed to permit the insertion of the tubing

for a sufficient depth so that a properly soldered

joint, as a rule, is stronger, in a short-time

tensile test, than the tubing or the fitting.

2. Diametral Clearance; Compositions of

Solder and of Metals Soldered

(a) Test Procedure

Tensile tests at room temperature, with a

speed of 0.06 inch per minute of the movable

head of the testing machine, were made on

joints having diametral clearances over the

range 0.002 to 0.060 inch. Some difficulty was

experienced in inserting the tubing into the

fittings when the difference between the mean

outside diameter of the tubing and the mean

inside diameter of the fitting was less than

0.001 inch. A satisfactory joint is generally

obtained if the tubing can be inserted into the

fitting by hand. When the clearance is greater

than 0.008 inch, there is difficulty in filling the

joint properly. The tubing and fittings, as furnished commercially, provide a diametral

clearance of 0.004 inch, that is, an annular

space aroxmd the tubing 0.002 inch in width.

For diametral clearances ranging from 0.002 to 0.008 inch, capillary action causes both types of

solders to flow readily to the extremities of the

overlap between tubing and fitting.

Heavy copper pipe and solid rod were used in

making the specimens for testing the eft'ect of

difterent clearances, because the thin-walled

tubing invariably broke before the joint did.

Figure 2.Specimen assembly

for tensile tests of joints with

different diametral clearances,

or different depths of bore.

Solid rod R was turned to diflterent diameters to vary clearance, when in- serted into sleeve S. Thickness of solder

film, C/2, is half of diametral clearance. Solid rod A was used as stop to fix depth

of insertion (bore depth) d.

T

1

-C/2

[5]
Both copper and brass (60 percent of copper,

40 percent of zinc) rods were used for one member of the joined specimens.

A section of the specimen assembly is shown

in figure 2. The sleeve, S, about 6 inches long, was cut from copper pipe having an inside

diameter of 0.628 inch. The diametral clear- ance, C, was varied by turning the solid rod,

R, to different diameters. Rod A was used as a stop to fix the bore depth, d, and was withdrawn after the jomt was soldered. Precautions were taken to locate the rod centrally

within the sleeve, S. In several specimens the

rod was mtentionally placed to one side of the

sleeve. The strength of such "off center"

joints was approximately the same as for ac- curately centered joints. Several joints were

sectioned longitudinally and were found to have

the annular space between the rod and sleeve

completely filled with solder. The sequence of the tests to determine the

effect of different clearances with different

solders and fittings was as shown in table 1.

(b) Discussion of Results

It was found that in short-time tensile tests the strength of joints between solid brass rods

and copper sleeves, test 1, varied among differ- ent specimens of approximately the same diametral clearance, and that the strength of joints increased with increase in clearances from

0.003 to 0.030 inch. For clearances from about

0.030 to 0.060 inch a slight decrease in strength was indicated. The results are plotted on

curve 1, figure 3. The strength of the joints in the short-time tensile tests was calculated in terms of shear stress on the soldered area at the

maximum tensile load. The soldered area was

calculated from the outside diameter of the tubing and the length of tubing inserted into the

fitting.

In most of the separated joints more solder was foimd adhering to the copper sleeve than to the brass rod. It was considered that differ- ences in absorption by the solder of zinc from

the brass might have caused the scatter in results in test 1 . Consequently, the ends of the

separated joints were reheated to melt the adhering solder, which was then wiped off with a

rag. The joints were again fluxed and re- soldered with new solder. The strength of the

resoldered joints was definitely higher, having

gained nearly 30 percent at all clearances over

that of the joints soldered only once. The

results are plotted on curve 2, figure 3. It was

noted that, in the joints separated after the

second soldering, more of the solder had adhered to the brass rods than was the case after the first soldering.

The separated joints from the second series of tests were again cleaned and made once more

with new solder. The results for these joints are plotted on curve 3, figure 3. It was found

that for joints with clearances up to about 0.010

inch a further increase in strength was obtained,

but that with greater clearances the strength of the joints soldered three times was about the same as that of the joints soldered twice.

It is noteworthy that only after the brass-tocopper joints had been soldered three times was

the strength of the joints with small clearances,

up to 0.010 inch, greater than that of joints with

larger clearances. It is a generally accepted

principle, based on numerous observations, that

when maximum adherence of solder to basis

metal is obtained, the thinner the film of solder

the stronger the soldered joint.

The residts of the short-time tensile tests on

joints between solid copper rods and copper

Table 1.Sequence of tests at different diametral clearances

Diametral

clearance

Joint members Solder Remarks

Inches

0.003 to 0.062

_

0.003 to 0.062. 0.003 to 0.062, 0.002 to 0.059_ 0.002 to 0.059 _ 0.002 to 0.059. 0.002 to 0.059. 0.002 to 0.059_ 0.004

Brass (60-40) rod and copper sleeve. dodo Copper rod and copper sleeve do

do , dodo

-do-

(50-50) tin-lead do

do

do

do

(95-5) tin-antimony

(49-49-2) tin-lead-zinc

(48.68-48.68-2.64) tin-lead-antimony _ 100 percent lead to 100 percent tin...

Resoldered after test 1. Resoldered after test 2.

Resoldered after test 4.

[6]
Figure 3.

Strength of soldered joints

at different diametral clearances.

Curves, 1, 2, and 3 for yellow-brass (60 copper,

40 zinc) rods soldered once, twice, and three

times, with (50-50) tin-lead, into copper sleeves. Curve 4, copper rod soldered into copper sleeve. Short-time tensile tests. Speed of movable head,

0.06 inch per minute.

6000

5000

UJ

q:

I-cn<

I 4000 cn

Z)X

% 0

( —J >

)

) 1

®

" o

® ®^ ®

o J

» ®

o

L 0

< ) ®

® /

n,

O

o

o

0.020 0.040

DIAMETRAL CLEARANCE

0.060

IN

slecA'es, made with tin-lead solder, were fairly

consistent, as indicated by curve 4, figure 3. The strength of these joints was considerably

greater than that of the brass-to-copper joints, even when the latter type had been soldered

three times. It is to be noted also that the

copper-to-copper joints with small clearances,

up to 0.010 inch, were stronger than when

larger clearances were used.

Resoldering the separated joints from test 4 did not result in a significant change in strength,

as is shown by curve 5, figure 4. Curve 4 from

figure 3, copper-to-copper joints soldered once,

is also plotted in figure 4 for ready comparison

with curve 5, copper-to-copper joints soldered

twice.

It was observed that in the separated copperto-copper joints a film of solder had adhered to both the copper rod and to the copper sleeve,

and to about the same extent in the joints

soldered once as in those soldered twice. Riipture had taken place by shear through the solder. Evidently the adherence of tin-lead solder to copper is stronger than it is to brass. Results of short-time tensile tests of the

copper-to-copper joints, soldered with (95-5)

tin-antimony (curve 6, fig. 4) showed that they were stronger, by about 13 percent, at all clearances than similar joints made with tin- lead solder. A definite indication was obtained that the

lower strength of the brass-to-copper joints,

6000

5000

UJ

a:

<

X 4000

(A

® J

5

^ 8

^

5 «

7 4

0 0.020 0.040

DIAMETRAL CLEARANCE IN. 0.060

Figure 4.

Strength of soldered joints

at different diametral clearances : cop- per rod and copper sleeve.

Curves 4 and 5, first and second soldering with

(50-50) tin-lead. Curve 6, for (95-5) tin-antimony

solder. Curve 7, for (49-49-2) tin-lead-zinc solder. Curve 8. for (48.68-48.68-2.64) tin-lead-antiniony

solder. Short-time tensile tests. Speed of movable head, 0.06 inch per minute.

247880°—40 2 [7]
Figure 5.

Strength of joints, copper

to copper, soldered with tin, lead, and

tin-lead alloys with different tin con^

tents.

Short-time tensile tests. Speed of movable

head, 0.06 inch per minute.

60

PERCENT

as compared to copper-to-coppcr joints, was

not due solely to differences in adhesion of the solder to the brass and the copper, but

partly, at least, to absorption by the solder

of zinc from the brass. Joints between copper

rods and copper sleeves were soldered with an

alloy containing equal parts of lead and tin and

2 percent of zinc. The results, plotted on

curve 7, figure 4, showed that the addition of

zinc to ordinary (50-50) tin-lead solder caused

a lowering of the strength in copper-to-copper

joints. These experiments indicated that zinc

should be kept out of tin-lead solders insofar

as possible.

Copper-to-copper joints made with (50-50)

tin-lead solder to which has been added 2.63

percent of antimony were not so strong as the

joints soldered with the (95-5) tin-antimony,

but were stronger than those soldered with

(50-50) tin-lead alloy. The results are plotted on curve 8, figure 4. These tests indicated that

the addition of antimony to (50-50) tin-lead

solder results in increased strength in the sol- dered joints. Further tests showed that joints

in the larger sizes did not fill as easily with

solders containing antimony as did those made

with (50-50) tin-lead solder. It is evident from figures 3 and 4 that there was no significant variation in the strength of the joint between copper rod and copper

sleeves for different diametral clearances up

to 0.010 mch.

Short-time tensile tests were made on a number of copper-to-copper joints soldered with

Figure 6.Strength of copper-to- copper joints, soldered with tin-lead and tin-antimony, in short-time tensile tests at 0° to 360° F.

Speed of movable head, O.Oti inch per minute.

8000

6000

<

LlI I

cn3

S

X

<

4000

2000

0

(95-5) TIN-ANTIMO it

(SO-SO) TIN -LEAD

100 200 300

TEMPERATURE °F

[8]
pure tin, pure lead, and alloys of various pro- portions of tin and lead, including the eutoctic

mixture of 63 percent of tin and 37 percent of

lead. The results plotted in figure 5 showed

that the joints soldered with the eutectic

mixture were stronger than those soldered with

other tin-lead alloys. It is more difficult to make sleeve joints with the eutectic mixture,

melting at a definite temperature, than it is to use the (50-50) tin-lead solder, having a melting range of about 55° F.

3. Tests at 0° to 350° F on Joints Made

With (50-50) Tin-Lead and With (95-5)

Tin-Antimony Solders

Figure 6 shows the results obtained on a

series of short-time tensile tests (speed of movable head 0.06 inch per minute) at 0°, 85°, 175°,

250°, 325°, and 350° F on joints made with

(50-50) tm-lead solder; and at 0°, 85°, 250°,

and 325° F on joints made with (95-5) tin- antimony solder. For the tests at 0° and 85°

F, the joints were made with ^-inch solid copper

rod inserted into couplings made from %-inch

iron-pipe-size copper pipe, because the strength

of "standard" tubing and couplmgs was not

adequate to support the loads necessary to rupture the solder films at these temperatures.

The maximum shear stresses for tests at 85° F

on joints made with %-inch type K tubing and

commercial wrought-copper couplings (results

not plotted in fig. 6) were somewhat lower than

those obtained from the copper rod and pipe

combinations. The tubing and couplings

showed considerable distortion after fracture

of the joints, which apparently caused the

lower maximum shear stresses. Type L tubing

and wrought-copper couplmgs were adequate

for the tests at 175° F and higher. The depth

of bore in the couplings was % inch, and the

diametrical clearance for all of the joints was

0.004 ±0.0006 inch.

For the elevated-temperature tests the speci- mens were heated by an electric furnace sur- rounding the specimen. The temperature of the specimen was measured with thermocouples

peened into the tubing at each end of the coupling. The tests at 0° F were made with the

specimens immersed in a bath consisting of

equal volumes of ethylene glycol and water

cooled with solid carbon dioxide.

The markedly higher strength of the joints of

0° F as compared to that at 85° F and the rapid

decrease in strength as the temperature was

increased above 85° F are in qualitative agree- ment with the results that would be expected

from tensile tests of the solder alloys themselves,

although not in quantitative agreement at any

of the temperatures. It is noteworthy also that the joints made with tin-antimony solder

did not lose strength as rapidly as did those

made with tin-lead solder, as the temperature was increased above 85° F.

VI. JOINTS MADE WITH (50-50) TINLEAD SOLDEK

Nmnerous tests, the results of which are not

given in detail in this paper, showed that the

strength of joints made with tin-lead or tin- antimony solders, in short-time tensile tests made at room temperature, was practically

equal to that of the hard-drawn type K tubing,

and generally greater than that of hard-drawn

types L and M tubing, and of all three types

in the annealed condition. Creep at room temperatures shown by the soft-solder alloys under

sustained tensile loads was encountered also in

joints soldered with these alloys. Sleeve joints

in copper tubing made with tin-lead may fail by shear in the solder fihn in about 40 days,

under sustained tensile loads only one-tenth as great as the loads necessary to rupture the

joints in short-time tensile tests. The rapid increase in creep rates of the soft- solder alloys with increase in temperature [16] is also a factor in determining the strength of soft- soldered joints in copper tubing when sucti tubing is subjected to temperatures above room

temperature. Time and temperature are therefore two interdependent variables affecting the

loads necessary to cause creep and rupture in soft-soldered joints. The conditions in the

solder films in sleeve-type joints in tubing are such that these loads cannot be ascertained from

the known or determined creep rates of the

solder alloys themselves.

As a basis for limitations that might be

imposed on installations of copper tubing as- sembled with sleeve-type soldered joints, it is

[9]
important to know the maximum stresses that can be imposed continuously on the joints without causing slip, extension, or rupture, in the

solder films, during the normal life expectancy of the installations. In addition to information on

the strength at atmospheric temperatures, it is necessary to know the rate at which the strength

decreases as the temperature is increased.

By means of a simple lever-system loading

device, figure 7, specimens with soldered joints were subjected to constant tensile loads for extended periods at room and at elevated temperatures. Four test racks were constructed,

each accommodating nine specimens loaded

independently. A load as high as 4,000 pounds

could be applied to each specimen. Calibration with proving rings showed that the loads

applied to the specimens were within one-half

percent of the loads calculated from the lever

ratio and weights on the weight pan.

7 L

50" -I

W

Figure 7.

Sketch of loading device for maintaining

constant tensile load on soldered joints in copper

tubing.

Gage marks, for measuring extensions in upper and lower joints in eouplinK, at G.

1. LoNG-TiME Tests at Room Temperature

(about 85° F)

The specimens for long-time tests at room

temperature consisted of lengths of %-inch type

L hard-drawn tubing connected in series with

four straight couplings, two of wrought copper

and two of cast brass. The diametral clearance

at the upper joint in each coupling was 0.008

inch; that at the lower joint on each coupling was 0.004 inch. These clearances had a toler- ance of ±0.0006 inch. The tubing (0.875 inch

O. D.) was inserted into the coupling to a depth

of 0.87, 0.95, or 1.01 inch, ±0.01 inch. The

soldered areas were calculated from these di- mensions. As a tensile load on the specimen

produced a stress predominantly in shear on the

solder film, the shear stress calculated from the

load and soldered area provided a common basis

for evaluating the strengths of the joints having

dift'erent dimensions.

The annular space between the tubing and

coupling was filled with solder by the conventional procedures recommended for installa- tions in buildings. Sectioning of extra joints

made for the purpose indicated that the annular

spaces on the specimens used for the long-time

tests were completely filled. This was verified

when the joints were sectioned after the tests had been completed.

Suitable gage marks were attached firmly to the tubing and coupling at each joint. The

extension of the joint resulting from slip or shear in the solder film was indicated by the in- creased distance between the gage marks, which was originally in the range 0.02 to 0.04 inch.

These distances were measured with a traveling

microscope to a precision of 0.0001 inch. The

accuracy of the measuring instrument was

checked with a standard scale and was well

within the precision of measurement. It was

considered that total extensions of 0.001 inch

or less, in the joints, were not significant. In

addition to the obvious failures in the joints

under sustained tensile loads, it was considered

that joints which were not visibly ruptured

would fail eventually if there was an increasing

curvature away from the line of zero extension,

in a curve of extensions plotted against time.

When one of the eight joints in a specimen had

failed, a pin inserted in a hole drilled thi'ough

the overlapping coupling and tube keyed the

failed joint and the remaining joints in the

specimen were retained under the original load.

Loads ranging from those causing no measureable extensions during 10,000 hours to those

[10]
causing failure of the joints in a few hundred

hours were applied to a sufficient number of specimens, each with eight joints, to obtain a

valid estimate of the maximum shear stress that could be sustained by the joint under

continued tensile load.

Observed extensions plotted against time, for representative joints in copper couplings made

with tin-lead solder, are given in figure 8. Similar data for joints in cast brass couplings

are given in figure 9. Results are given only

for joints with 0.004-inch diametral clearance.

The extensions observed on the upper joints of each coupling, with 0.008-inch diametral clearance, were in general greater than on the joints

with 0.004-inch clearance. The latter clear- ance is the average obtained within the present

tolerances for dimensions of tubing in the

nationally recognized standards * and in a proposed standard ^ for cast and wrought sleevetype fittings. The clearance of 0.008 inch was

obtained by cutting down the outside of the

tubing or enlarging the bore of the coupling.

As the maximum permissible stress estimated

for the joints with 0.008-inch clearance was not

significantly less than that for the joints with

* See footnotes 2 and 3.

' Proposed American Standard, "Soldered-Joint Fittings."

aoo8

0.004

0

CURVE LOAD LB SHEAR STRESS LBiAk'- 1038 400

2 1036 375

3 658 250

4 698 235

5 41 1 160

2000 4000

TIME HOURS

6000

Figure 9.Extension-time curves for

joints in type L tubing with cast- brass (85 copper, 5 tin, 5 zijic, 5

lead) couplings: soldered with (50—

50) tin-lead.

Diametral clearance, 0.004 inch. Tests at room temperature (85° F).

11
0.004-inch clearance, it was not considered

necessary to present detailed data on the

joints with the larger diametral clearance.

It is evident from an inspection of the cm"ves,

figures 8 and 9, that the joints in the copper

couplings would eventually fail when subjected

continuously to a tensile load causing a shear

stress on the soldered area of 275 pounds per

square inch or greater. In the joints with the

cast-brass couplings, eventual failure was indicated at shear stresses of 250 pounds per square

inch or greater. No significant extensions, nor

increasing rates of extension, were observed in

joints with either type of coupling, at shear

stresses of 235 pounds per square inch or less. Although data presented cover a period of

7,500 hours, the tests at the lower stresses were

continued to 10,000 hours with no change in the

extensions. On the basis of these results it was

concluded that 235 pounds per square inch

(658-pound tensile load on %-inch tubing) was a

conservative value of the maximum shear

stress on the soldered area that can be maintained for an indefinitely long time at room

temperature (85° F) by sleeve-type joints made

with (50-50) tin-lead solder. The temperature

of the testing laboratory fluctuated about

10° F plus and minus, from the 85° F value

indicated as room temperature.

It is noteworthy that the maximum permissible shear stress (235 pounds per square inch)

in the tin-lead solder films for joints subjected

to continued tensile loading at 85° F is only

Yis of the ultimate shear stress in short-time

tests of similar joints, and only jii of the ulti- mate shear stress in joints between copper rod

and heavy-walled copper pipe (fig. 6).

2. LoNG-TiME Tests at 85° F on Joints in

3-INCH Tubing

A number of specimens of joints in 3-inch

copper tubing, soldered into cast-brass couplings with tin-lead solders, were subjected to sustained tensile loads causing shear stresses on

the soldered areas of 235 pounds per square

inch to determine whether the larger size would

have any significant effect on the strength of

the joint.

Joints were made with two types of 3-inch

tubing, type K with a wall thickness of 0.109

inch and type O with a wall thickness of 0.049

inch, type O being commonly used in sizes of

3 inch and over. The outside diameter of both types was 3.125

inches, and the tubing was inserted into the couplings to a depth of 1 % inches. The diametral

clearance was 0.004 ±0.001 inch. For a shear

stress of 235 poimds per square inch on the

soldered film, the tensile stress in the tubing- was 4,200 pounds per square inch for type K

and 9,100 pounds per square inch for type O.

No distortion of the tubing was to be expected

at such low tensile stresses. The tests were continued to approximately

9,000 hours. Several joints in type K tubing

and one in the type O tubing failed after 3,000

to 5,000 hours. It was found, after the failure,

that the solder had filled only from 60 to 80

percent of the annular space between the tubing

and coupling, so that the actual shear stress in

the solder films was greater than 235 pounds

per square inch. Several other joints which

had not failed were found to have more than 90

percent of the annular space filled with solder. It was concluded that 235 pounds per square

inch on the solder film, determined as the maximum allowable shear stress for continued loading at 85° F for joints in the %-inch tubing,

would apply also to larger tubing, but only

when 90 percent or more of the annular space

between tubing and couplings was filled with

solder. It was found practically impossible to completely fill the joints on tube sizes of 2 inches

and larger, with the ordinary soldering technique, probably because the entire circumfer- ence of the tubing and coupling cannot be

brought to the proper soldering temperature at the same time. In using the value 235 pounds

per square inch as the maximum allowable

shear stress on the solder film for continued

tensile loading of the joint, a greater allowance

for imperfections in soldering should be made

for joints in tubing larger than 2 inches than

for joints in smaller tubing.

3. Long-Time Tests at 123°, 173°, 218°, and

250° F

To determine the effect of temperatures

above 85° F on the long-time strength of joints

[12]
made with tin-lead solder, tests similar to those

described for the room-temperature tests were made at 123°, 173°, 218°, and 250° F. Each

specimen contained two joints, one at each end

of a straight coupling. Type L, hard-drawn

tubing, %-inch nominal size, was used with

wrought-copper and cast-brass couplings from

several sources. The portion of the specimen

containing the coupling and its two soldered

joints was enclosed in a heating chamber constructed from 2}^-inch glass tubing, closed at the top and bottom with asbestos board, as shown in figures 10 and 11. Helically wound

heating elements were placed on suitable

supports, within the glass chamber. Thermocouples peened into the middle of the

couplings were used to indicate the temperatures. There was no significant temperature

gradient along the length of the coupling, and

the temperatures were constant to within plus

or minus 7° F of the test temperatures. The

deviations from a constant temperature were

considered not to have a significant effect on

the results obtained with this type of test. Extensions in the joints were measured with

the same measuring microscope used for the

room-temperature tests, sighted through the

glass walls of the heating chamber. The microscope is shown in position for observing in

figure 10. Fine marks made with a razor blade on short wires soldered to the coupling and tube

at each joint were used as gage marks.

Figure 10 shows a group of nine specimens

mounted in the testing fixtures. Figure 11 is a close-up view of two specimens, with the

heating chamber lowered from the coupling of one specimen. The wires containing the gage

marks are visible on the latter specimen.

Figure 10.

Specimens of soldered joints mounted in fixtures for elevated-temperature tests at constant tensile loads.

Glass-walled heating chambers, F, enclose couplings. Leads T to thermocouple peened into middle of coupling. Potentiometer P connected through switches S to thermocouple leads. Extensions between gage marks measured with measuring microscope M.

[13]
Figure 11. — Close-up view of two specimens.

Heating chamber lowered from coupling of specimen at right. Gage marks placed on wires G soldered to tubing and coupling. Heating

element, R; power leads, P. For the tests at 123°, 173°, and 218° F, the

tubing was inserted into wrought-copper cou- phngs to a depth of 0.87 ±0.01 inch. For the

upper joint in each couphng the diametral

clearance was 0.008 inch; for the lower joint,

0.004 inch. The tolerance on both these dimensions was 0.0006 inch.

Tensile loads of 660, 410, and 285 pounds were

applied to specimens maintained at each of the

three temperatures 123°, 173°, and 218° F. The shear stresses on the soldered areas cor- responding to the three different loads were 275,

170, and 120 pounds per square inch. Observations of extensions in the joints were made

daily in the early parts of the tests and at

suitable intervals, the length of which depended

upon the rates of extension, throughout the

duration of the tests. Some of the tests were

prolonged to 12,000 hours.

The observed extensions for the three shear

stresses are plotted against time in figure 12

for the tests at 123° F, in figure 13 for the tests at 173° F, and in figure 14 for the tests at 218° F. Early failure occurred in the joints

held at 173° F at a shear stress (on the soldered

area) of 275 pounds per square inch, and the

extensions were so large that they could not

be plotted in figure 13 on the scale used for this graph. The deviations of the plotted points

from a smooth curve, figures 12 to 14, were the

result of measuring extensions on only one

side of the specimens. The joints undoubtedly

did not extend uniformly around the circumference. The deviations from uniform extension were much smaller than the total extensions,

indicating eventual failure ; and it was concluded

that gage marks placed on only one side of the

specimen were adequate for the purpose.

[1-t]
Figure 12.

Extension-time curves for

joints in type L tubing with copper

couplings; soldered with {50-50) tin- lead.

Tests at 123° F.

Oj040

0.030

0.020

0.010

0

0

It is evident from an inspection of the ciu"ves

that the joints with a diametral clearance of

0.008 inch extended at a significantly greater

rate than did those with a clearance of 0.004

inch, at each of the loads and temperatures.

Furthermore, the joints with 0.008-inch clear- ance were extending at an increasing rate,

indicating eventual failure. At 123° F, the joints with 0.004-inch clear- ance and subjected to shear stresses of 120 and

170 pounds per square inch showed no signifi- cant extensions in 8,800 hours. In preliminary

experiments, similar joints, held at 123° F, were extending at an increasing rate under shear

stresses of 208 poimds per sc^uare inch. It was

concluded, therefore, that 170 pounds per square

0.040

0.030

1 0.020

COz

UJ

I-2 0.0 I 0

CURVE LOAD LB SHEAR STRESS LB/iN* CLEARANCE IN

1 660 275 0.004

2 660 275 ox)oe

3 410 1 70 0.004 4 4 10 170 aoo8

9 2 85 120 0.004 6 289 120 0.008 V'

-^^0 5 2000 4000

TIME

6000

HOURS

8000

inch was the maximum allowable shear stress for joints with 0.004-inch clearance held continuously at 123° F. At 173° F the joints

loaded to a shear stress of 170 pounds per square

inch were extending at a rate indicating eventual failure. At a shear stress of 120 pounds per

square inch, the joint with 0.008-inch clear- ance extended at a rate indicatmg eventual fail- ure. The joint in the same specimen, but with

only 0.004-inch clearance extended only 0.006

inch dvu^ing the first 7,000 hours and showed

no further extension during the next 5,000

hours. It was concluded that 120 poimds per

square inch was the maximum allowable shear

stress for joints with 0.004-inch clearance, held

continuouslv at 173° F.

2/

•

, —-—

•""

4

•

1

y •

CURVE LOAD LB SHEAR STRESS LB/iN* CLEARANCE IN

1 410 170 0.004

2 4 10 170 0.008

3 285 120 0.004

4 2 85 120 0.008

0—o-Kxr^

no o " u °u o4000

TIME

8000

HOURS

2000

Figure 13.—"Extension-time curves for

joints in type L tubing with copper

couplings: soldered unth (50-50)

tin-lead.

Tests at 173° F.

[IS]
Figure 14.

Extension-time curves for

joints in type L tubing with copper

couplings; soldered with (50-50)

tin-lead.

0 1000 2000 3000

TIME HOURS

The curves of figure 14 show that a shear

stress of 120 pounds per square inch on the

soldered area would cause eventual failure at 218° F. It is evident also that the joints with

0.008-inch clearance extended at a more rapid

rate, at each of the three stresses, than did the

joints with 0.004-inch clearance.

For the tests at 250° F, all the joints were made with a diametral clearance of 0.004 inch

(±0.0006 inch). The specimens were held in a vertical position for making the joints.

Hence, for the upper joint in the coupling, the

solder ran into the annular space between the

tubing and the coupling, aided by gravity,

while for the lower joint the solder filled the

space by capillary action, against gravity.

For one series of tests the tubing was in- serted into the couplings to a depth of 0.87 inch

(±0.01 inch). The joints were subjected to

tensile loads causing shear stresses on the

soldered areas of 70, 80, 90, and 100 pounds per

square inch. The tests were continued to 7,500

hours. The observed extensions were plotted

against time, in figure 15 for the lower joints

and in figure 16 for the upper joints of the

specimens. There were no significant dift"er- ences between the upper and lower joints on the same specimen, indicating that good agreement
can be expected in duplicate specimens. The

results also showed that joints filled against

gravity can be expected to have the same properties as those made "down-hand" or in a

horizontal position.

The joints in copper couplings stressed to 70,

80, and 90 pounds per square inch on the

soldered areas extended rather rapidly during

the first 1,500 hours at 250° F; but the extensions came to a halt, and the extension-time

curves (Nos. 1, 2, and 3, figs. 15 and 16),

became horizontal thereafter, indicating per- manence under the conditions of test. The joints stressed at 100 pounds per square

inch likewise extended at a more rapid rate during the first 1,500 hours than thereafter; but

the joints continued to extend, at a slower rate (curve 4, figs. 15 and 16), to the end of the test, 7,500 hours, indicating eventual failure. One specimen in the series of tests at 250° F

was made with a cast-brass coupling, and the

joints were stressed at 90 pounds per square

inch. The extensions during the early part of

the test (curves 5, figures 15 and 16) were

gi'eater than those in the wrought couplings at the same stress, but came to a halt after about

3,000 ho\u-s with no further extension to 7,500

hours.

Another series of tests at 250° F were made

on specimens in which the joints were made hy

inserting the tubing mto wrought-copper couplings to depths of 0.40, 0.61, 0.87, and 1.50

0.030

CURVE LOAD LB DEPTH OF BORE IN

1 • 100 0.40

2 0 1 52 0.6 1 3 • 2 1 7 0.87

4 e 373 1.50

0 2000 4000 6000

TIME,' HOURS

8000

Figure 17.Extension-lime curves for

joints in type L tubing with copper

couplings ; soldered with {50-50) tin- lead.

Diametral clearance, 0.004 inch. Depth of in- sertion varied from 0.40 inch to 1.50 inch. Loads

varied accordingly, to make shear stress on soldered

area 90 pounds per square inch on each joint. Tests at 250° F.

[17]
inches. The specimens were loaded so that the

shear stress on the soldered area of each joint was 90 pounds per square inch. The observed

extensions, on the lower joints of the couplings

only, are plotted against time, to 7,500 hours

in figure 17. The extensions of the upper

joints were very closely the same as those of the

lower joints.

These extension-time curves are in general

like those for the joints stressed at 90 pounds

per square inch in figures 15 and 16. The

results show that increasing the length of

soldered area in the joint increases the loadcarrying capacity up to the point where the

shear stress, on the soldered area, approaches

the critical value for the temperature of service.

The rather large differences in total extensions on difi'erent specimens, stressed at 90 pounds

per square inch on the soldered areas of the

joints, and the larger deviations from a uniform

rate of extension than were obtained at lower

shear stresses were considered to indicate that

90 pounds per square inch was probably on the

border line between stresses that would cause eventual failure and those that could be

sustained permanently, at 250"^ F.

It was concluded, therefore, that 80 pounds

per square inch was a more conservative value

of the maximum allowable shear stress on the

soldered area of sleeve-type joints in wroughtcopper or cast-brass couplings, made with

(50-50) tin-lead solder and held continuously

at 250° ¥.

The marked change to a lower rate of extension after about 1,500 hours at 250° F might

be explained by a constitutional change in the

tm-lead solder film. A further indication of

this was the fact that the load on the specimen

stressed at 70 pounds per square inch (curve 1, figs. 15 and 16) was increased after 5,000

hours to cause the shear stress on the soldered area to be 90 pounds per square inch (same

value as curve 3, figs. 15 and 16). However,

no measurable extension occurred as a result of the increase in stress. Metallographic examination of solder films

from joints held at 250° F for 1,500 hours or more showed that copper had dift'used into the

tin-lead solder from the brass or copper couplings and from the copper tubing. Increased

resistance to shear stresses would be expected

from the addition of copper to the tin-lead

solder film. Further discussion of this phenomenon is given in a subsequent section of this paper.

VII. MAXIMUM SHEAR-STRESS—TEMPERATURE RELATIONS FOR JOINTS

MADE WITH (50-50) TIN-LEAD SOLDER

The maximum allowable shear stresses indicated by the results of the long-time tests at

85°, 123°, 173°, and 250° F described above are

listed in table 2 and plotted in figure 18 to show the stress-temperature relation. Joints

300

[18]
with 0.004-mch diametral clearance, made

with (50-50) tiii-lead solder, can be expected

to withstand continuous loading without failure by shear in the solder fihn when subjected to combinations of stress and temperature, repre- sented by points to the left and below the

curve, figure 18. Joints subjected to stresses and temperatures to the right and above this curve can be expected to faU eventually by

shear in the soldered film. It is probably more than a coincidence, and

represents the behavior of the materials concerned, that the product of stress and temperature, at the four experimentally determined

points, figure 18, is approximately a constant.

Table 2

Maximum allowable shear stress on soldered areas of joints made with tin-lead and tin-antimony

solders, at the indicated temperatures

Tempera- Tin-lead Tin-antimony

ture (50-50) (95-5)

o f Iblin.i Ib/inJ 86 235 1, 200

123 170

173 120 250 80 380

325 275

VIII. MAXIMUM INTERNAL-PRESSURE—TEMPERATURE CURVES FOR

JOINTS IN COPPER TUBING MADE

WITH (50-50) TIN-LEAD SOLDER

The maximum shear stress-temperature re- lations shown in figure 18 were used by

Subcommittee No. 11, American Standards

Association Sectional Committee A40, as the

basis for establishing internal pressure-temperature ratings in the Proposed American

Standard for Soldered-Joint Fittings. In ordinary circumstances the shear stress on the

soldered film in sleeve-type joints is caused

primarily by the internal pressure in the tubing.

At a given pressure the shear stress varies

directly with changes in length of the soldered

area. As this length is fixed by the dimensions

of the fitting, it was desirable to standardize

the dimensions of the fittings for the dift'erent sizes of tubing. It was obviously impractical

to make the depths of the bores of the fittings

that is, the distance to which the tubing is to be inserted into the fitting—such that the

shear stresses on the soldered areas at a given

pressure would be alike for all the commercial

sizes of tubing. Some compromise was neces- sary to keep the fittings for the larger sizes of

tubing to reasonable dimensions.

For the tentative draft of the Proposed American Standard for Soldered Joint Fittings, Subcommittee 11 selected the values given in

table 3 for minimum depth of bore, for commercial sizes % to 6 inches. Joints, in fittings

with these depths of bore, made with (50-50)

tin-lead solder were considered to have adequate strength for pressures likely to be en- countered in ordinary domestic water-service

piping. Table .3 gives the internal pressures in

/8- to 6-inch tubing necessary to develop a shear

stress of 235 pounds per square inch on the

soldered areas of the joints. The results of the

long-time tests described above (see figs. 8 and

9) indicated 235 pounds per square inch as the

maximum for sustained loading at room temperature (to 85° F). The pressures were cal- culated by use of the formula:

where P is the internal pressure in pounds per

square inch (gage), L is the depth of bore

(inches) , D is the outside diameter of the tubing

(inches) , S is the shear stress (pounds per square

inch).

Table 3.Internal pressures corresponding to maximum

allowable shear stress on tin-lead soldered areas of joints dimensioned as in columns 1 and 2, and for

shear-stress temperature relations as given in figure 18

Internal pressures Nominal Depth of

size of bore of 2351b/in.2= 1701b/in.2= 1201b/in.2= 80 lb/in.2= tubing ' fitting 2 max shear max shear max shear max shear

stress at stress at stress at stress at 85° F 123° F 173° F 250 °F

Inches Inches lb/in.' (gage) lb/in.^(gage) lb/in. ^ (gage) Iblin.' (gage) H H 705 510 360 240

Vi H 750 545 385 255 H H 805 585 410 275

1 15/16 785 565 400 265 m 1 685 495 350 230 m m 650 470 330 220

2 m 610 440 310 210 2H VA 535 390 270 180

3 liHe 510 370 260 170 3H 505 365 260 170

4 2^6 500 360 255 170

5 21H6 495 360 250 170

6 3^ 480 350 245 165

I ASTM and Federal specifications.

' ASA proposed standard. The maximum pressures that can be maintained without eventual failm'e decrease with

19]
increase in temperature, in the same relation as do the shear stresses (fig. 18). With the above

formula the internal pressures corresponding

to the maximum shear stresses at 123°, 173°,

and 250° F have been calculated for sizes from %

to 6 inches. These values are also included in

table 3 . The curves, figure 19, show the maximum

internal pressure-temperature relations for (SOSO) tin-lead soldered joints for some of the commercial sizes of tubing. These relations for

sizes not in the range plotted can be gotten

by interpolation.

Apart from the fact that the fittings should

not be rated for pressures corresponding to the

maximum strength of the soldered joints, allow- ance should be provided for imperfectly soldered

joints and for stresses imposed on the joints

from sources other than the internal pressure in

Table 4.-Pressure ratings for joints made with {50-50)

tin-lead solder ^

Service tempertures

Service pressure ratings at temperatures from 100° to 250° F

Fluids other than steam Steam

Nominal sizes 2 in. and

smaller

Nominal sizes 2^2 in. and

larger

Nominal sizes

all

°F

100

150 200

250

Ib/inJ (gage) 175

125 10075

lb/in. ^ (gage) 150 100

7550

lb/in J (gage)

15

1 Pressure ratings are less than half the values shown on figure 19. Joints made with (50-60) tin-lead solder are not recommended for temperatures above 250°F.

the tubing. Subcommittee 11 decided that an ample margin of safety would be provided by

the ratings in table 4, selected for the tentative

draft of the Proposed Standard for SolderedJoint Fittings. These ratings fall well below

the curves, figure 19. The determination of the ratings for these

fittings illustrates a practical use of the results

of the strength tests described in the foregoing

sections of this paper.

IX. JOINTS MADE WITH (95-5) TINANTIMONY SOLDER

The short-time tensile tests at room and at elevated temperatures, described in section V,

showed that joints soldered with (95-5) tin- antimony alloy required much greater loads to cause rupture in the solder films than did joints

soldered with (50-50) tin-lead alloy. The shorttime tests showed also that the tin-antimony

soldered joints did not lose strength as rapidly „ as did the tin-lead soldered joints when the f temperature was raised above 85° F. jj

1. LoNG-TiME Tests at Room Temperature ! (about 85° F)

Specimens similar to those used for the tests

j on tin-lead soldered joints were prepared for

] sustained tensile load tests on joints made with

(95-5) tin-antimony solder. The tests were j made at 85°, 250°, and 325° F. For the tests

[20]
at 85° F, four specimens, each containing four

couplings, were used. Two of the couphngs

were cast brass and two were wrought copper.

The upper joint of each couphng was made with

0.008-inch diametral clearance and the lower

with 0.004-inch clearance. Most of the joints

made with the larger clearance failed at shear

stresses that did not cause measurable ex- tensions in the joints with 0.004-inch clear- ance. The results of the tests at 85° F carried to 7,500 hours showed that the joints with 0.004

inch (±0.0006 inch) clearance, consisting of %-inch type K tubing soldered into copper or

cast-brass couplings, would withstand without

failure sustained tensile loads causing shear

stresses on the soldered area up to 1,200 pounds

per square inch. This was about five times the

stress obtained for (50-50) tin-lead soldered

joints in similar tests. A noteworthy observation was that no measlu-able extensions were obtained in the tin-antimony soldered joints prior to visible rupture.

Extension-time curves such as were obtained

for the tin-lead soldered joints (figs. 8 and 9) could not, therefore, be plotted.

2. LoNG-TiME Tests at 250° and 325° F

For the sustained-load tests at elevated temperatures, the specimens and equipment were

like those used for similar tests on the tin-lead

soldered joints, figures 10 and 11. At 250° F,

four specimens, each with two joints, were subjected to loads causing shear stresses on the

soldered area of 590, 540, 480, and 430 pounds

per square inch, respectively. All failed by

rupture of the solder fUm, without previous visible extension (more than 0.001 inch), in from

920 hours for the most heavily loaded to 3,600

hours for the joint under the lowest stress. Additional specimens loaded to shear stresses on the soldered area of 380 and 350 pounds per

square inch did not fail to show any significant

extension in the joints in 5,000 hours. These

results could be considered to indicate that

joints between copper tubing and copper sleeves

made with (95-5) tin-antimony solder, would

support continuously, at 250° F, tensile loads

causing shear stresses in the soldered films not exceeding 380 pounds per square inch.

It was found, however, upon examination of

segments cut from such joints, that had been

exposed continuously to 250° F, for several

thousand hours, that the bond between the

solder and copper had been significantly weakened. The segment of tubing coidd be "peeled"

from the surrounding piece of coupling by hand.

Metallographic examination showed that this condition resulted from dift'usion between the

copper and solder. Examination of similarly soldered joints ex- posed to a temperature of 325° F for several

thousand hours and more showed that interdiflusion between copper and the tin-alloy

solder was more projiounced than at 250° F. In segments cut from the joints, the tubing

dropped from the surrounding coupling without application of any force. The "solder"

film was slate-colored and very brittle, and

could be "peeled" from the copper. The sur- face of the copper, was blackened, apparently

by an oxide film. In the sustained tensile-load tests at 325° F,

the joints were initially subjected to loads causing shear stresses on the soldered areas of 80 to 275 pounds per square inch without any significant extensions m 2,500 hours. The loads were mcreased at intervals, until failures were

obtained, after 7,500 hours, in the jomts having

shear stresses exceeding 400 pounds per square

inch. The failures occurred by rupture in the

solder film without any previous extension.

However, joints loaded initially to a shear

stress (on the soldered area) of 400 pounds per

square inch failed within a few days, with considerable extension before rupture took place in

the solder film. Evidently, despite the loss of bonding

strength that initially exists between the solder

and the copper resulting from dift'usion in the

solder film, the joint is "keyed" against slipping

to an extent that permits the joint to support

higher loads than can be supported initially.

Such joints, not retaming the origmal contmuous metal bond between the solder and the copper, are not necessarily leak-proof and would be

expected to be subject to localized corrosion

along the solder film. Observations on joints soldered with pure

tin confirmed the indications that the rate of

diffusion between copper and tin-alloy soft sol-

[21]
ders increased with increase in tin content of

the solder. Although the maximum stress that could be

supported continuously without failure at 325° F was not determined, the results of the

tests, extended to 7,500 hours indicated that

joints made with the tin-antimony solder would

not fail under shear stresses not exceeding 275 to 300 poimds per square inch (at 325° F).

However because of the diffusion that takes

place between the tiii-alloy solders and copper

at temperatures above about 250° F, and the

resulting loss of bonding strength, it is considered that such solders should not be used in

joints subjected contmuously to temperatures

above 250° F.

X. MAXIMUM SHEAR-STRESS—TEMPERATURE RELATIONS FOR JOINTS

MADE WITH (95-5) TIN-ANTIMONY

SOLDER

The results of the long-time tests at 85°,

250°, and 325° F indicated that the maximum

allowable shear-stresses on the soldered areas

of joints in copper tubing soldered into copper

sleeves with (95-5) tin-antimony alloy were as

listed in table 2. Although tests at other temperatures, particularly between 85° and 250° F,

should be made to locate accurately the stress- temperature relations shown by the curve,

figure 20, it is considered that the maximum

allowable stresses at all temperatiu-es between

85° and 250° F can be estimated with sufficient accuracy for design purposes from this curve. Prolongation of the curve beyond the 250° F

point should not be considered justification for use of this solder at temperatures in this range.

The maximum stress-temperature curve for

joints soldered with tin-lead alloy (fig. 18) has

been replotted, to a different scale for stress, in figure 20, for a comparison with a similar curve for joints made with tin-antimony solder.

It is evident that the pressure ratings, table 4

and figure 19, provide a considerably greater

margin of safety with the (95-5) tin-antimony

solder than with the (50-50) tin-lead solder, at temperatures up to 250° F.

XI. FLUCTUATING TENSILE LOAD

TESTS ON JOINTS MADE WITH (50-50)

TIN-LEAD SOLDER

The tests described in the foregoing sections were made under continuous loading without

intermittent unloading. Piping in household

plumbing, as well as in other installations, is subject to vibration. It was considered that

the behavior of soft-soldered joints in copper

tubing under repeated stressing, such as would

occur in vibratory action, was of sufficient importance to warrant investigation.

Specimens consisting of type L copper tubing

soldered into wrought-copper couplings with

(50-50) tin-lead alloy were subjected to pulsating tensile loads in machines used previously

[22]
for pulsating tensile-load tests on wire.® The

loads ranged from the minimum available, which

produced a shear stress on the soldered area of

the joint equal to 40 pounds per square inch, to those which caused failure by fracture of the

coupling or tubing or by shear in the solder

film, after a few thousand cycles. The loads

changed from minimum to maximum 20 to 25

times per minute. All tests were made at room

temperature.

It was found that at a range of shear stress on the soldered area of 300 pounds per square

inch (40 to 340 pounds per square inch) or less, failures were not obtained in 2 million cycles. Tests were not continued beyond this number

of cycles. It was considered more important to obtain data on a number of specimens under

similar stress ranges than to prolong the test to the conventional 10 million (for steels) or 100

million (nonferrous) cycles used in determinations of fatigue limits. Four specimens were tested at the stress range

of 300 pounds per square inch. The tensile

load ranged from 96 to 720 pounds. On two of the joints the extensions, after 2 million cycles, were of the order of 0.001 inch, an amount considered to be insignificant. On the other two

joints the extensions were 0.009 and 0.021 inch,

respectively, amounts indicating the joints

would ultimately fail if the stressing were continued. At higher stress ranges, fractures were

obtained in the solder films and in the couplings

or tubing. As 235 pounds per square inch was

determined to be the maximum stress, on the

soldered area, that could be withstood without

eventual failure by joints subjected to steady

tensile loads, the results of the pulsating tensile- load tests were considered to indicate that this limit would apply also to joints loaded repeatedly in tension.

With the equipment available, it was not

possible to make repeated loading tests on sol- dered joints with the load cycle ranging from

tension to compression.

XII. SUMMARY

1. Short-time and long-time tensile tests have

been made on sleeve-type joints in types K and

'W. H. Swanger and G. F. Wohlgemuth, Failure of heat-treated steel wire in cables of Ml. Hope R. I. suspension bridge. Proceedings American

Society for Testing Materials 36, fig. 14, p. 48, and fig. 24, p. 69 (1936).

L copper tubing, soldered into wrought-coppcr

and cast-brass couplings with (50-50) tLu.-k;ad and (95-5) tin-antimony alloys.

2. A number of investigations made elsewhere

have shown the marked decrease in strength of

tin and lead alloys similar to those commonly

used as soft solders, as temperature and time

under load are increased. However, the

strength of soldered joints, including sleevetype joints in copper tubing, cannot be esti- mated from residts of tests on specimens of the

solder alloys themselves.

3. In addition to time and temperature, other

variables aft'ecting the strength of sleeve-type

joints in tubing include:

(a) Depth of bore in the fitting.

(b) Diametral clearance, that is, thickness of

the annular space between tubing and fitting,

filled with solder.

(c) Kind of metal used for fittings.

4. Short-time tensile tests showed that the

strength of joints soldered with (50-50) tin- lead solder increased in an approximately direct

proportion to the increase in depth of bore in

wrought-copper and cast-brass fittings (fig. 1). In straight couplings conforming to commercial

standards the depths of bore are sufficient so

that, in short-time tensile tests, the strength of the soldered joints is substantially equal to that of the coupling or tubing.

5. Results of short-time tensile tests at room

temperature showed that joints made with (50-

50) tin-lead and (95-5) tin-antimony solders

with diametral clearances up to 0.010 inch were

slightly stronger than were similar joints with

greater clearances. The joints soldered with

(95-5) tin-antimony were about 13 percent

stronger at all clearances (to 0.06 inch) than were those soldered with (50-50) tin-lead (fig. 4).

6. Joints in wliich one member was yellow

brass (60 copper, 40 zinc) soldered with (50-50)

tin-lead, had slightly lower strength at small

diametral clearances than at clearances greater

than about 0.010 inch. When the same joints were resoldered twice, the strength at the smaller

clearances increased. Further investigation in- dicated that this behavior was related to absorption by the solder of zinc from the brass (fig. 3).

7. In short-time tensile tests, copper-tocopper joints with nominal clearance (0.004

inch), soldered with the eutectic composition of

[23]
tin-lead (63 percent tin, 37 percent lead) had

higher strength than similar joints soldered with

pure lead, pure tin, or other proportions of tin and lead (fig. 5).

8. In short-time tensile tests (speed of movable head 0.06 inch per minute) the strength of

joints soldered with (50-50) tin-lead, calculated

as shear stress on the soldered area for maximum load, decreased from 8,000 pounds per

square inch at 0° F to 600 pounds per square

inch at 350° F. For similar joints soldered with

(95-5) tin-antimony, the maximum shear stress decreased from 8,300 pounds per square inch at 0° F to 1,800 pounds per square inch at 325° F

(fig. 6).

9. The results of sustained tensile-load tests at room temperature (85° F), continued as long

as 10,000 hours, indicated that the maximum

shear stress on the soldered area without extensions indicating eventual failure was 235 pounds

per square inch for joints in /4-inch tubing

made with (50-50) tin-lead solder. This value

held for cast brass (85 copper, 5 tin, 5 zinc 5, lead) as well as for wrought-copper couplings,

and for diametral clearances of 0.004 and 0.008

inch. This value was also found to hold for similar joints in 3-inch tubing (figs. 8 and 9). 10. Results of long-time (7,500 to 8,500

hours) tests under sustained tensile loads at temperatures above 85° F showed that the

maximum shear stress on the soldered area that

could be supported without extension indicating

eventual failure, in joints soldered with (50-50)

tin-lead, was 170 pounds per square inch at 123° F (fig. 12), 120 pounds per square inch at 173° F (fig. 13), less than 120 pounds per square

inch at 218° F (fig. 14), and only 80 pounds per

square inch at 250° F (figs. 15, 16, and 17).

These values hold for wrought-copper and

cast-brass fittings, with diametral clearances of 0.004 inch. Joints having clearances of 0.008

inch may fail at the above stresses.

11. From the maximum shear-stress-temperature relations (fig. 18 and table 2) the corre- sponding internal pressures, in pounds per

square inch gage, were calculated for the nominal

tube sizes % to 6 inches (fig. 19 and table 3). 12. In the Proposed American Standard for Soldered-Joint Fittings prepared by Subcommittee No. 11, American Standards Association

Section Committee A40, the adjusted pressure

ratings for joints made with (50-50) tin-lead

solder (table 4) were based on the maximum

shear-stress-temperature relations given in this paper (fig. 18 and table 2). 13. Results of sustained tensile-load tests at 85° F showed that joints in %-inch tubing sol- dered with (95-5) tin-antimony solders and

wrought-copper or cast-brass couplings withstood shear stresses on the soldered area up to 1,200 pounds per square inch without extension

indicating eventual failure. This value is five times that determined for similar joints soldered

with (50-50) tin-lead.

14. At 250° and 325° F the maximum allowable shear stresses for joints soldered with

(95-5) tin-antimony were found to be 380 and

275 pounds per square inch, respectively. The

maximum shear-stress-temperature curve for (95-5) tin-antimony soldered joints is therefore

considerably higher than that for (50-50) tin- lead soldered joints (fig. 20). In the long-time

tests of the joints soldered with (95-5) tin- antimony, failure generally occurred by rupture

in the solder film, without prior extension of the joint. In the joints soldered with (50-50)

tin-lead, an increasing rate of extension of the

joint was the criterion of failure.

15. In the long-time tests on joints soldered

with (95-5) tin-antimony those with a diametral clearance of 0.008 inch extended more

than did those with a clearance of 0.004 inch

at the same stresses.

16. In the joints used in the elevated-temperature tests, diffusion of copper into the solder

films was foimd to occur at temperatures of 250° F and above. The diffusion increases

with increase in temperature above 250° F,

and also with increase in tin content of the

solder. In joints soldered with (95-5) tin- antimony, exposed for 5,000 hours at 325° F,

the metallic bond between the solder and the

tubing was destroyed. At 250° F the bond was

significantly weakened. With (50-50) tin-lead

solder, difFiision at 250° F is considerably slower.

The results of the elevated-temperature tests indicated that joints in copper tubing made

with tin or tin-alloy solders should not be

subjected continuously to temperatures above

250° F.

17. Results of pulsating tensile-load tests at room temperature indicated that joints soldered

[24]
with (50-50) tin-lead solder could withstand for

2 million cycles repeated stressing to the max- imum shear stress on the soldered area found

for sustained tensile loading.

Acknowledgment is made for assistance in

the conduct of this investigation received from

various members of the staff of the National

Bureau of Standards, particularly the Division

of Metallurgy. Grateful acknowledgment is made also for helpful advice and suggestions

received from J. A. Doucett, Chairman, Executive Committee, and B. B. Caddie, Secretary,

Copper and Brass Research Association.

XIII. SELECTED REFERENCES

[1] G. O. Hiers, Soft solders and their applications,

Metals & Alloys 2, 257 (1931).

[2] S. J. Nightingale, The Jointing of Metals. Part

I. Soft Solders and Soldered Joints, Brit. Non-Ferrous Metals Research Assn., Research

Reports, No. C 234/214 (Dec. 1936).

[3] D. J. Macnaughtan, E. S. Hedges, and W. R.

Lewis, Solder, Int. Tin Research Development

Council, Bui. No. 2 (1935).

[4] B. W. Gonser and C. M. Heath, Physical properties

of soft solders and the strength of soldered joints, Trans. Am. Inst. Mining Met. Engrs. 123, 349

(1936).

[5] I. T. Hook, Methods of joining copper alloy products,

parts I, II, and III, Tubes, etc.. Metal Ind. (N. Y.) 35, 434, 498, and 555 (1937).

[6] E. J. Daniels and D. J. Macnaughtan, The Wetting

of Metals by Metals with Particular Reference

to Tinning and Soldering, Tech. Pub. Int. Tin

Research Development Council, [B] No. 6 (1937).

[7] A. W. Coffman and S. W. Parr, Surface tension of metals with reference to soldering conditions, Ind. Eng. Chem. 19, 1308 (1927).

[8] R. S. Dean and R. V. Wilson, Action of fluxes in

soft soldering and a new class of fluxes for soft soldering, Ind. Eng. Chem. 19, 1312 (1927).

[9] A. Eyles, Some practical notes on solders and solder- ing fluxes. Metal Ind. (London) 40, 3 (1932).

[10] C. L. Barber; Soft solder fluxes, Ind. Eng. Chem.

29, 1114 (1937).

[11] J. R. Freeman, Jr., and G. W. Quick, Tensile properties of soldered joints under prolonged stress. Metal Ind. (N. Y.) 24, 7 (1926).

[12] R. Chadwick, The influence of surface alloying on

the strength of soft soldered joints, J. Inst. Metals

62, 277 (1938).

[13] C. W. Hill and C. H. Carpenter, Strength of solders

at elevated temperatures, Metal Ind. (N. Y.) 17, 82 (1919).

[14] D. Hanson and E. J. Sandford, The creep of tin and

tin alloys—Part I, J. Inst. Metals 59, 159 (1936).

[15] J. McKeown, Creep of lead and lead alloys. Part

I—Creep of virgin lead, J. Inst. Metals 60, 201

(1937).

[16] W. A. Baker, The creep properties of soft solders and

soft-soldered joints, J. Inst. Metals 65, 277 (1939).

[17] M. S. Noyes, The Navy's soldered fittings, J. Am.

Soc. Naval Engrs. 47, 57 (1935). Washington, May 24, 1940.

[25]

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