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2. weight loss

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u
g
min
cuming
you.
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Avon, MA 02322.1148
1.800.432 .6464
Fax 508.580.0960
www.cumingcorp.com
PRODUCT INFORMATION AND TECHNICAL DATA
ESTIMATING HYDROSTATIC PERFORMANCE
DISCLAIMER: This note is provided for general information only and is not an engineering specification; it should
never be used for designing or specifying materials or products. Data for any specific purpose or application must
be requested from and verified by the manufacturer.
48
6464
m
Technical Note 100-2-A
PRODUCT INFORMATION AND TECHNICAL DATA
TECHNICAL
NOTE 100-2-A
DISCLAIMER: This note is provided for general information only and is not an engineering specification; it should
Page 1 of 2
Estimating Hydrostatic PErformancE
never be used for designing or specifying materials or products. Data for any specific purpose or application must
be requested from and verified by the manufacturer.
INTRODUCTION
[2]
CAL NOTE
100-2-A
Syntactic foam may lose some portion of its buoyancy when
WP = X(Log NH) + Y
WHERE:
WP = Percent weight gain = 100( ΔW/W), %
subjected to hydrostatic pressure. Most of the initial loss is due
ΔW = Weight gained due to water absorption, lbs
to elastic compression, whereas most of the long-term loss is
W = Initial weight before test, lbs
due to water absorption. Understanding the loss mechanism enN = Number of cycles to pressure
[2]
WP = X(Log NH) + Y
TION
ables the designer to manage short and long-term behavior.
This
H = Total number of hours at pressure
ay lose somenote
portion
of itsabuoyancy
provides
few ruleswhen
of thumb for estimating
WHERE: the
WP approxi= Percent weight gain = 100(
%
Log ΔW/W),
= Logarithm
to base 10
ostatic pressure.
of of
theimmersion
initial losson
is syntactic
due
mateMost
effects
foam.
ΔW = Weight gained due to water
absorption,
lbs
X,Y = Dimensionless empirical constants
ssion, whereas most of the long-term loss is
W = Initial weight before test, lbs
For a single hydrostatic test, N = 1.0. Factors X and Y can be
ELASTIC
LOSS
rption. Understanding
the loss
mechanism enN = Number of cycles to pressure
used as needed to adjust results to match known data. If testto manage Elastic
short and
This to hydrostatic pressure
H = Total
number of hours at pressure
losslong-term
is directlybehavior.
proportional
and
ing is being performed at rated service pressure PR and no prior
w rules of thumb
for estimating
thetoapproxi= Logarithm
10
inversely
proportional
the bulk modulus of the Log
syntactic
foam, to base
data is known, X may be assumed in most cases to be 1.0 and
mersion on syntactic
foam.
as expressed
in Equation 1:
X,Y = DimensionlessYempirical
constants
= 0, and Equation
2 takes on its simplest form WP = Log H as
For a single hydrostatic test, Nillustrated
= 1.0. Factors
X and1.Y can be
in Figure
[1]
VP = 100(P/K)
OSS
used as needed to adjust results to match known data. If testWHERE:
VP = Percent
change
in volume = 100( ΔV/V), %
ctly proportional
to hydrostatic
pressure
and
1
ing is being performed at rated FIGURE
service pressure
PR and no prior
ΔV of
= Change
in volume
of pressurization,
onal to the bulk modulus
the syntactic
foam,as a result
data is known, X may be assumed in most cases to be 1.0 and
cubic ft
quation 1:
Y = 0, and Equation 2 takes on its 3.0%
simplest
— form WP = Log H as
V = Original volume before pressurization, cubic ft
illustrated in Figure 1.
00(P/K)
P = Hydrostatic pressure, psi
—
rcent change in volumeK==100(
ΔV/V),
% of syntactic foam, psi
Bulk
modulus
FIGURE 1
2.0% —
hange in volume
as a result
of typically
pressurization,
Syntactic
foam is
designed so that volume strain VP
bic ft
—
WP
is 1.0% at rated service pressure PR. Therefore, bulk modulus
3.0% —
iginal volume
before
pressurization,
cubic
ft
can be estimated as K = 100 x the hydrostatic pressure at rated
1.0% —
drostatic pressure,
psi
service depth.
Volume strain in syntactic foam of —
3.0% or more
Weight Gain % = WP = Log H
ulk modulus may
of syntactic
foam, psi
—
lead to catastrophic
collapse, crushing, and permanent loss
ating Hydrostatic PErformancE
2.0% —
—
—
—
—
—
—
—
—
—
—
—
—
—
—
typically designed
so that volume strain VP
of buoyancy.
0% —
—
WP
rvice pressure PR. Therefore, bulk modulus
24
72
120
168
216
264
312
ABSORPTION
as K = 100 xWATER
the hydrostatic
pressure at rated
1.0% —
H,HOURS
ume strain inThe
syntactic
3.0%under
or more
rate at foam
whichofwater
pressure enters the cellular struc-Weight Gain % = WP = Log H
—
Estimated weight gain due to water absorption versus time at
rophic collapse,
crushing,
and
permanent
ture of
syntactic
foam
tends toloss
diminish over time,
similar to the
constant pressure PR.
logarithmic function in Equation 2:
0% —
—
—
—
—
—
—
—
—
—
—
—
—
—
—
SORPTION
24
72
PAGE 2
120CONT. ON168
H,HOURS
216
264
312
water under pressure enters the cellular strucdue cannot
to water
absorption
time
at
is an uncontrolledweight
documentgain
and therefore
be assumed
to be currentversus
or accurate;
it should
oam tends to diminish over time, similar toWARNING:
the This note Estimated
constant
pressure
never be used for designing
or specifying
materialsPor
R.products. Data for any specific purpose must first be requested from
on in Equation 2:
and verified by the manufacturer.
Cuming Corporation Technical Note 100-2-A
Date of last revision: July 11, 2012
and verified by the manufacturer.
CONT. ON PAGE 2
WARNING: This note is an uncontrolled document and therefore cannot be assumed to be current or accurate; it should
never be used for designing or specifying materials or products. Data for any specific purpose must first be requested from
and verified by the manufacturer.
Cuming Corporation Technical Note 100-2-A
Date of last revision: July 11, 2012
call Toll Free: within USA 800-432-6464 or ++508-580-2660 or visit: www.afglobalcorp.com/cumingcorp
Technical Note 100-2-A
Page 2 of 2
SAFETY FACTOR
FIGURE 3
The rate of water absorption is inversely proportional to the
safety factor, or ratio of crush pressure to rated service pressure,
as shown in Equation 3:
[3]
SF = PC /PR
SF = Safety factor, dimensionless ratio
PC = Crush pressure or hydrostatic strength, psi
PR = Pressure at rated service or intended use
depth, psi
WHERE:
The offshore industry standard for marine riser is API 16F, which
specifies a minimum safety factor of 1.25 for syntactic foam
buoyancy modules on drilling risers. This is the idealized service
condition upon which Figure 1 is based. As shown in Figure 2,
lesser SF increases the rate of water absorption while greater SF
lowers the water absorption rate. This gives rise to the general
rating practice shown in Figure 3.
—
Non-critical/short-term:
expendable or one-time use
1.25
General purpose:
drilling risers, ROVs, most buoys
1.50
Long-term:
production risers, subsea equipment
2.00
or More
Critical/safety:
man-rated submersibles, safety devices
Note: These ratings are for general guidance only and should not be used
without consulting the manufacturer or cognizant regulatory agencies.
Water absorption is primarily a surface phenomenon and proportional to surface area, whereas weight and buoyancy are
volume-related. The result is that percent weight gain is influenced by the area-to-volume (A/V) ratio of the buoy. A large simple shape generally has a small A/V ratio (less weight gain)
while a small complex shape has a larger A/V ratio (more
weight gain). And it must be remembered that weight gain percentage is not always the same as buoyancy loss percentage,
since the relative proportions of weight and buoyancy vary as a
function of syntactic foam density.
5.0 —
—
4.0 —
—
R = Relative Rate of Water Absorption
—
OTHER EFFECTS ON PERFORMANCE
2.0 —
API 16F
—
1.0 —
—
0—
1.00
Less Than
1.25
AREA-TO-VOLUME RATIO AND
DENSITY EFFECTS
6.0 —
3.0 —
TYPICAL USES OR APPLICATIONS
Typical syntactic foam depth rating practices.
FIGURE 2
R
SAFETY
FACTOR
SF=PC /PR
1.25
1.50
1.75
SAFETY FACTOR SF=PC /PR
2.00
Typical effect of hydrostatic pressure on rate of water absorption.
Pressure cycling has a fatigue effect on syntactic foam that can
be estimated by using the N factor in Equation 2. Raising the
water temperature will also increase the water absorption rate;
specially formulated high temperature epoxy binder materials
are available to address this problem. Attempts to develop
“accelerated” testing methods have not been entirely successful, so that careful extrapolation from reliable historical longterm test data remains the best way to predict performance. It is
recommended that users contact Cuming Corporation for
expert assistance in designing syntactic foam products. For
more information, see our web site www.cumingcorp.com.
Page 2 of 2
call Toll Free: within USA 800-432-6464 or ++508-580-2660 or visit: www.afglobalcorp.com/cumingcorp