Nonferrous for Heat Exchangers, · PDF filetAlloys for Heat Exchangers, Pumps, and Piping ......
Transcript of Nonferrous for Heat Exchangers, · PDF filetAlloys for Heat Exchangers, Pumps, and Piping ......
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Fatigue Properties o f NonferroustAlloys for Heat Exchangers,
Pumps, and Piping
Assignment 86 1o8MEL R&D Report 232/66
May 19656
By
M. R. Gross and R. C. Schwab
U. S. NAVY1
MARINE ENGINEER-ING LABORATORYI
II apolis, Md/O t P ~ ,~
.601
DedicatcM To- PROGRESS IN MARINE ENGINEERIN(e
Bet.st Available, Copy
Distribution of this document is unlimited.
~O6 4'?~b OO
Fatigue Properties of NonferrousAlloys for Heat Exchangers,
Pumps, and Piping
Assignment 86 108MEL R&D Report 232/66
May 1966
By
M. R. Gross and R. C. Schwab
M. R. GROSS
R. C. SCHWAB
Approved by:A
)istribution of thi~g"G~~umv,,,t is ur ime- d
46 t% T%
ABSTRACT
The fatigue behavior of 13 nonferrous
alloys used for corrosion-resistant heat
exchangers, pumps, and piping systems was
investigated over a broad life spectrum of
100 to 100-million cycles. Both cast and
wrought copper-base and nickel-base alloys
were studied. It is concluded that wrought
Monel* and forged Ni-Al bronze have the
highest fatigue strengths, whereas gun metal
and valve bronze have the lowest. The effect
of salt water on fatigue performance was not
found to be highly significant. The use of
Langer's equation to predict stress-cycle
relationships gave satisfactory results for
wrought alloys but appeared to be overly con-
servative for cast alloys.
II
*Registered trade name of the International Nickel Company,Incorporated. C
iii
MEL Report 232/66
TABLE OF CONTENTS
Page
!RIBUTION LIST ii'RACT iii:ODUCTION 1:RIALS INVESTIGATED 2[OD OF TEST 2oURE CRITERIA 4rLTS OF TESTS 5'ARISON OF FATIGUE STRENGTHS 6!LUSIONS:RENCES
8
OF FIGURESFigure 1 - Drawing, Rotating Cantilever Beam
Fatigue SpecimenFigure 2 - Drawing, Low-Cycle Fatigue SpecimenFigure 3 - Curve, Flexural Fatigue Curves, Gun Metal
(Cast)Figure 4 - Curve, Flexural Fatigue Curves, Valve
Bronze (Cast)Figure 5 - Curve, Flexural Fatigue Curves, Ni-Al
Bronze (Cast)Figure 6 - Curve, Flexural Fatigue Curves, Ni-Al
Bronze (Forged)Figure 7 - Curve, Flexural Fatigue Curves, Superston
40 (cast)Figure 8 - Curve, Flexural Fatigue Curves, 70-30
Cupronickel (Cast)Figure 9 - Curve, Flexural Fatigue Curves, 70-30
Cupronickel (wrought)Figure 10 - Curve, Flexural Fatigue Curves, 90-10
Cupronickel (Hard)Figure 11 - Curve, Flexural Fatigue Curves, Cufenloy
40 (Annealed)Figure 12 - Curve, Flexural Fatigue Curves, Cufenloy
40 (DSR)Figure 13 - Curve, Flexural Fatigue Curves, Cupro-
nickel 707 (Wrought)Figure 14 - Curve, Flexural Fatigue Curves, Monel
"E'T (Cast)Figure 15 - Curve, Flexural Fatigue Curves, Monel
(Wrought)
v
Introduction
Many copper-base and nickel-base alloys are used in the con-
struction of heat exchangers, pumps, and piping systems designed
to handle fresh or saline water. In the selection of materials
for such applications, consideration is given primarily to corro-
sion resistance, erosion resistance, and heat transfer charac-
teristics. In most applications the applied stress levels are
low. Accordingly, the structural strength properties of the
materials are relatively unimportant.
In recent years, more and more attention has been given to
the structural properties of these alloys because of (1) cost and
weight reduction programs, (2) conservation of strategic materials,
(3) development of new high-strength alloys, and (4) new applica-
tions which impose high stress levels. Typical of the latter are
sea-connected cooling systems for hydrospace vehicles.
One of the most likely modes of mechanical failure in systems
undergoing cyclic pressurization or thermal shock loading is
metal fatigue. The frequency of stress cycling in such systems
may vary from that of an occasional start-up and shutdown to
vibrational forces developed by the movement of the heat-exchanger
fluids. Little or no published information on the alloys used in
this type of service was found in reviewing the literature several
years ago. Accordingly, tests were conducted at the U. S. Navy
Marine Engineering Laboratory to establish the fatigue behavior of
1
ariety of corrosion-resistant nonferrous alloys. The results
these tests are presented in this paper.
.erials Investigated
The 13 alloys investigated are listed in Table 1, together
-h their chemical compocitions and tensile properties.
.luded are the strength coefficient, K, and strain-hardening
)onent, n, contained in the true-stress/true-strain relaticn-
Lp:
a = K en
re are some deficiencies in the tensile properties of the cast
:erials with respect to the governing specifications. This is
be expected inasmuch as the specification requirements are
aally based on separately cast test coupons, whereas the values
ven in Table 1 were obtained on specimens removed from cast
ates.
thod of Test
Two types of flexural fatigue specimens were used in the
vestigation. The high-cycle fatigue tests were performed with
tating cantilever-beam specimens having the dimensions shown in
gure 1. These were constant deadweight load tests with a cycle
equency of 1450 cpm. The smooth test lengths were circum-
rentially and longitudinally polished to a metallographic
nish.
2
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t5 U u ,Itu -t Qc j
The low-cycle fatigue tests were performed with equipment
ibed previously.' Flat flexure-type specimens having the
sions shown in Figure 2 were used. The short end of the
men was held stationary, while the long end was flexed
en mechanical stops by a hydraulic piston. One or more
n gages (0.25-inch gage length) were attached to the mini-
est section to record the longitudinal strain. The applied
ng force was measurpd with a load cell. The total strain
ACT, was obtained from strain gage readings, and the
al bending-stress range was calculated from elastic stress
las using the measured load range. Specimens were cycled
^pm.
All of the fatigue tests were of the completely reversed
(Fatigue ratio = -1). Whereas most of the specimens were
d in air, a few were tested with Severn'River water con-
usly wetting the test surface. Severn River water is a
ish estuary water containing 1/6 to 1/3 the salt content
tural seawater, depending on the season and the tide.
ous fatigue tests in both Severn River water and natural
ter havF. shown no significant differences in the effects
e two media.
re Criteria
Failure in the high-cycle, rotating cantilever-beam tests
sted of complete fracture. Failure in the low-cycle fatigue
4
tests was defined as one or more surface cracks 3/16 to I/4 inch
in length.
Results of Tests
The results of the tests are plotted in log-log form in
Figures 3 through 15. Two methods have been used in analyzirvj
the data. The top graph in each figure is the SR vs N relation-
ship for the data, where SR is the nominal reversed bending
stross and N is Lhe number of cycles to failure. SR was calcu-
lated from the elastic stress formula
SR =21~
where AM = bending moment range, in-lb.
c = distance from neutral axis to outermost fiber at
minimum cross section, in.
I = moment of inertia of minimum cross section, in.4
The bottom graph in each figure is the SPE vs N relationship
for the data, where SPE is the reversed pseudoelastic or apparent
elastic stress calculated as follows:
SPE = 6ET.E ..... (2)
2
where ACT = total strain range as determined from strain gages
on the test section, in/in.
E = modulus of elasticity (Table 1), psi.
5 -
urvilinear relationship between Spr and N was obtained by
fitting the following relationship to the data.
_PE = c + SE .....
Nm
C and m = best-fit constants
SE = endurance limit or fatigue strength at 10s
cycles, psi.
_st-fit equation for the SPE vs N data is given in each
a.
Equation (3) is a generalization of the following equation
sed by Langer 2 for predicting the SPE vs N fatigue curve
tensile test data.
_ E in ( 00 +S ..... (4