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HYDROGEN INDUCED DISBONDING: FROM LABORATORY TESTS TO ACTUAL
FIELD CONDITIONS
L. Coudreuse, S. Pillot, P. Bourges Centre de Recherche des
Matriaux du Creusot (CRMC)
INDUSTEEL Creusot B.P. 19, 71202 Le Creusot
France
A. Gingell Chateauneuf plant
INDUSTEEL France B.P. 68, 42803 Rive-de-Gier
France
ABSTRACT
Disbonding tests are often required during fabrication of
hydrotreating vessels. However it is
difficult to make the link between the testing conditions and
the actual service conditions in the reactor wall. From numerical
simulations of hydrogen profiles through disbonding test specimens
and reactor walls it is possible to assess both the severity of
disbonding tests and the actual risk of disbonding in service. It
is shown that in-service temperature and hydrogen pressure are
important parameters that control hydrogen distribution throughout
the wall of a reactor, however, the influence of the wall thickness
will also be underlined: the greaterer the thickness of the vessel,
the greaterer the risk of disbonding. On the basis of a data bank
of disbonding test results performed for fabricators world-wide, a
proposal is made to adapt the severity of the test to the severity
of the service conditions (pressure, temperature, wall thickness).
Keywords: Disbonding, Hydrogen Induced Disbonding, Hydrotreatment,
2.25Cr-1Mo, 1.25Cr-1Mo, V modified grades.
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INTRODUCTION
Hydrogen Induced Disbonding, called Disbonding in the following,
can occur after cooling down of hydrotreating reactors which
operate at elevated temperature under high hydrogen pressure.
Disbonding, is characterized by a crack propagating at the
interface between the base material, and the austenitic stainless
steel weld overlay or cladding (In the paper, overlay will be use
to describe both weld overlay and cladding). It is the consequence
of both hydrogen over-saturation at the interface after cooling
down and the presence of a sensitive microstructure at this
interface [1]. Typical hydrogen profiles through the wall of a
reactor in service, steady state condition, and after cooling down,
are shown on Figure 1. During operation, there is a linear gradient
of hydrogen content in the stainless steel overlay and in the base
material. There is more hydrogen in the stainless steel overlay
than in the base material because of the higher hydrogen solubility
in the austenitic stainless steels. The increase of hydrogen
content at the interface is the consequence of the variation of
hydrogen diffusivity and solubility laws when the temperature
decreases. As will be explained later, there is diffusion of
hydrogen from the parent material to the weld overlay, but since
the diffusion coefficient of hydrogen is low in the overlay, there
is a strong increase of hydrogen at the interface.
An API survey, conducted several years ago, on heavy wall
reactors has revealed that out off 100
reactors investigated, twenty-eight (28) exhibited some form of
disbonding [2]. The operating conditions of most of these reactors
were in the following range: Temperature (455C- 466C/850F- 870F)
and hydrogen partial pressure (138- 245 bar/ 2000- 3450psi). Since
then the question of disbonding resistance of stainless steel weld
overlays has become a question of great concern. More and more
specifications for hydrotreating vessels are asking for disbonding
tests. In 1996, an ASTM standard was published to describe the way
to run a test [3]. More recently API publication 934 [4], which
describes materials and fabrication requirements for heavy wall
pressure vessels for high temperature and high hydrogen pressure
service, introduced a requirement for disbonding tests. However,
both the ASTM standard and the API publication are not clear on the
testing conditions to be used. An industry joint research program
conducted in Europe led to the conclusion that in many cases, use
of actual service conditions for testing, (hydrogen pressure and
temperature), results in excessively severe test conditions
[5].
The objective of this paper is to discuss the influence of
several parameters, (hydrogen pressure, temperature, cooling rate,
thicknesses), on the increase of hydrogen content at the interface
and to demonstrate why the use of actual service conditions for
disbonding tests may result in too severe conditions. On the basis
of numerical calculation and test results, a matrix of disbonding
test conditions is proposed based on the severity of in-service
conditions.
DESCRIPTION OF HYDROGEN ENRICHMENT AT THE INTERFACE Why is there
hydrogen enrichment at the interface?
Figure 1 describes the hydrogen profile in a reactor wall at the
interface, for the steady state condition and after cooling down.
Knowing the hydrogen diffusivity and solubility laws for both
the
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base material and the weld overlay, it is possible to determine
the hydrogen profile in steady state condition.
C0, Hydrogen concentration in the overlay at the internal
surface, can be calculated from the Sievert laws. C0 = pH21/2*S (1)
p2: Partial hydrogen Pressure S : Hydrogen solubility in the
austenitic stainless steel
C01 and C02 are the hydrogen concentration at the interface in
the overlay and in the base material respectively. At the
equilibrium, the hydrogen activity is the same in the two
materials, then: C01/ C02 = S/S (2) S : Hydrogen solubility in the
base material
It can also be established that the ratio C0/C01 can be
calculated from the following formula [6]: C0/C01 =1+ (S/S)*(D/D)
*tov/tbm (3) tov : Overlay, or cladding, thickness tbm: base
material thickness
In order to calculate, the hydrogen concentration at the
interface after cooling down, it is necessary to consider that
there is at any time, t, an equilibrium between the hydrogen
activity at the interface in the base material and in the weld
overlay: Ct1/ Ct2 = S()/S() (4) S() and S() are the values of the
hydrogen solubility respectively in the overlay and in the base
material at the temperature T (in K) corresponding to time t.
The evolution of hydrogen solubility with temperature can be
expressed by an Arrhenius law: S =So*exp (-E/RT) (5)
Figure 2 shows the relationship between hydrogen solubility and
1000/T for an austenitic stainless steel and a 2.25Cr-1Mo low alloy
steel. The following laws, well accepted for the two materials have
been used [6]: S = 33*exp(-3333/T) (6) S = 8.93*exp(-650/T) (7)
The solubility is expressed in ppm bar1/2
At 450C (1000/T = 1,383), the ratio between the hydrogen
solubility in the austenitic stainless steel and the base material
is about 11. There is 11 times more hydrogen in the overlay than in
the base material at the interface. When the temperature decreases
to room temperature (1000/T = 3,356), the ratio increases to about
2200. The increase of hydrogen content in the overlay, close to the
interface, can be explained by this increase of the ratio S/S.
Since the hydrogen solubility remains high in the overlay there is
diffusion from the base material to the overlay. The maximum
hydrogen content
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depends also on a kinetic aspect, which can be described by the
diffusion coefficient. As shown in figure 3, the diffusion
coefficient in the austenitic material is very low, when compared
with the low alloy steel base material. At 450C, the difference is
about 2 orders of magnitude; at room temperature it is about 6
orders of magnitude. The following diffusion coefficient laws have
been used in Figure 3 [6]: D = 2.4*10-3 exp(-2132/T) (8) D =
7.1*10-4 exp(-4555/T) (9)
Diffusion coefficient is expressed in cm2/s
The low hydrogen diffusion coefficient in the austenitic
material explains the sharp aspect of the hydrogen peak in the
overlay. Difference between the hydrogen distribution in the wall
of a reactor and in a test specimen
In order to study disbonding resistance of overlay, specimens
are exposed in an autoclave under hydrogen pressure at elevated
temperature. After exposure and cooling at a selected cooling rate,
the amount of disbonded area is evaluated through UT
examination.
Different specimen sizes have been used for disbonding tests.
Figure 4 shows examples of
specimens used. Figure 4a represents a parrallelepipedic
specimen, used by the authors of this paper, while figure 4b
represents the specimen described in the ASTM standard G146. The
main difference between the two specimens is the presence of a side
austenitic weld overlay in the case of the ASTM specimen. The
reason for this side overlay is to avoid hydrogen diffusion from
the cylindrical surface of the specimen. It has been shown with
numerical calculations, that if the cooling rate is high enough
(Greater than 150C/H), the hydrogen content at the interface in the
middle of a parrallelipedic specimen is the same than for the ASTM
specimen. However for both types of specimen, the hydrogen exposure
consists in the exposition of the whole specimen under hydrogen
pressure in an autoclave. When the time necessary to achieve a
saturation of hydrogen in the specimen is achieved (steady state
condition), the specimen is cooled at a specified cooling rate. So
in the steady state condition in the specimen a homogeneous
hydrogen distribution at the interface is obtained (Figure 5). C0 =
pH21/2*S (10) C0 = pH21/2*S (11)
Then if the exposure condition in the autoclave corresponds to
the actual service conditions, it will result in higher hydrogen
content at the interface, at the steady state. The initial
conditions are not the same at the interface before cooling
down.
In order to determine hydrogen profile through the wall of a
reactor or in a test specimen, a finite element program has been
used. Hydrogen profiles have been calculated for a wide range of
conditions for the temperature, the hydrogen pressure, the cooling
rate, the base material thickness, and the overlay thickness. A
statistical analysis of the obtained results has permitted to
establish relationships between the different parameters and the
maximum hydrogen content at the interface, after cooling down, for
both a reactor wall and a laboratory test specimen [5].
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PARAMETERS ACTING ON MAXIMUM HYDROGEN CONTENT AT THE
INTERFACE
The occurrence of disbonding at the interface between an overlay
and the base material, depends on two kinds of parameters:
Parameters acting on the metallurgical quality of the interface,
and parameters acting on the amount of hydrogen at the interface.
The quality of the interface, its sensitivity to disbonding, depend
on the base material composition and more particularly, on its
carbon content[7], the welding conditions when apply, the overlay,
and the PWHT[8]. It is not the purpose of the paper to describe the
influence of these parameters. Then for a given quality of the
interface, the occurrence of disbonding will depend on the hydrogen
content at the interface. Disbonding will occurs when a critical
hydrogen concentration will be reached.
According to formulas (1),(2),(3) and (4), the hydrogen content
at the interface after cooling down depends on the following
parameters. Hydrogen pressure (pH2) Temperature (T)
Hydrogen diffusion coefficient and hydrogen solubility laws for
the overlay and the base material (D(T); D(T); S(T) and S(T)) Base
material thickness (tbm) Overlay thickness (tov) Cooling rate (Cr):
An average cooling rate value has been considered Time
In the following, the influence of these parameters on maximum
hydrogen content at the
interface, CHmax, is discussed. Influence of time:
During and after cooling, there is an increase of hydrogen
content at the interface. After a fast increase of hydrogen content
during cooling, there is a slower increase when the reactor remains
at room temperature. Maximum hydrogen content, CHmax, is obtained
after several hundred hours. As wall thickness increases, more time
is required to reach maximum hydrogen content [5]. For disbonding
test specimens, numerical simulations show that the maximum
hydrogen content is achieved within about 130h for a 40mm thick
specimen. This is in accordance with the experimental observation
which show that the amount of disbonding measured by UT increases
with time after cooling down.
Influence of hydrogen diffusivity and solubility:
The hydrogen profiles depend on the hydrogen solubility and
hydrogen diffusion coefficient in the base material and in the
overlay [5]. Lower increase of hydrogen at the interface is
obtained when the differences in hydrogen solubility and hydrogen
diffusivity between the two materials decrease. Then for a given
overlay, the choice of a base material with a low diffusion
coefficient and a high hydrogen solubility, such as V modified
Cr-Mo grades [9], will result in a lower CHmax values, than the one
obtained for a standard Cr-Mo grade working in the same condition.
However the hydrogen solubility and the hydrogen diffusion
coefficient are not known for each material used in the fabrication
of hydrotreating reactors, and even for a given material these
values can depend on slight variations in chemical analysis or on
the heat treatment. So for the following, we have considered the
solubility and diffusivity laws given by relationships
(6),(7),(8),and (9). Then, the CHmax value calculated cannot be
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considered as the exact hydrogen content at the interface for
each material combination. It can be considered as a value
indicating the severity of service conditions.
From the numerical calculations performed, it has been possible
to establish a formula [5].
CHmax (reactor) = f( T, pH2, Cr, tbm and tov) (12) Influence of
temperature, hydrogen pressure and cooling rate:
Figures 6 to 8 give the influence of pressure and cooling rate
on CHmax, calculated from relation (12), for different operating
temperature for a 250mm thick reactor, with a 6mm thick overlay. It
is not surprising to see that an increase of temperature or
hydrogen pressure results in higher hydrogen content at the
interface. There is not a big influence of cooling rate on CHmax,
this confirms the fact that degassing occurring during cooling down
is not efficient to reduce the amount of hydrogen in the
reactor.
The influence of wall thickness is shown on Figures 9 and 10.
Figure 9 gives the evolution of CHmax for a service temperature of
450C for hydrogen pressure between 50 bar and 200 bar and for a
wall thickness between 50 and 350mm. The figure clearly shows that
the wall thickness has a strong influence on CHmax. This can be
explained by the following reasons: . When the thickness decreases
there is more hydrogen diffusion to the atmosphere from the
external side of the reactor. There is less hydrogen available to
go to the interface. . According to formula (3), and (2), the
hydrogen contents at the interface, C01 and C02, increase when the
base material thickness increases. There is more hydrogen content
at the interface before cooling down in a thick reactor than in a
thin one, for the same operating conditions.
Figure 10 gives the influence of weld overlay thickness. It
shows that an increase of the weld overlay thickness reduces CHmax.
This is well explained by formula (3): C01 decreases when overlay
thickness increases.
These results confirm that disbonding is a more critical issue
for thick wall reactors. Thick wall reactors are also those
operating in the more severe service conditions (elevated
temperature and high hydrogen pressure).
SIGNIFICANCE OF DISBONDING TESTS
There are several possible objectives for a disbonding test. It
can be a quality control test, with fixed testing conditions,
assessing that the weld overlay or the cladding, give a sufficient
quality level by comparison with previous test results. A second
objective can be to have a test representative of service
conditions to ensure that the overlay will be exempt of problems in
service. In the first case, the test may not necessarily be
representative of service conditions; it can be more severe.
However, it is necessary to have sufficient feedback on in-service
behaviour to determine what the acceptance criteria must be for a
severe test. The first approach can only be used for comparison
purposes as it is not possible to determine acceptable disbonding
test results for a given service condition. In the second case, the
result of the test must be no disbonding.
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The second approach is probably more adapted to the
qualification of overlay procedures. However it is necessary to
have a disbonding test which can represent the actual situation of
a reactor wall. It means that CHmax in the disbonding test specimen
must be equal or close to the CHmax value obtained in the reactor
wall.
As for reactors, on the basis of numerical calculations,
performed for different specimen
thickness and for different exposure and cooling conditions, a
formula has been established between the maximum hydrogen content
at the interface, CHmax, and these parameters.
CHmax (specimen) = g(T, pH2, Cr, tbm and tov) (13)
Again the relationship has been established for the solubility
and diffusivity laws (6),(7),(8),and (9). It means, as, for reactor
walls, that the value is not necessary the actual value at the
interface. It can be considered as a value giving the severity of
the testing conditions.
In order to check if there is a relation between the disbonding
test and the hydrogen content at the interface, a series of tests
have been conducted for a wide range of conditions (temperature,
hydrogen pressure, cooling rate, and specimen thickness), for the
same overlay condition. Figure 11 represents the relation between
the percent of disbonded area on the surface of the specimen (D%),
determined by UT, and the calculated CHmax. The figure clearly
shows that below a critical hydrogen content at the interface,
about 375ppm, there is no disbonding, while the amount of disbonded
area increases with CHmax values higher than 375ppm. This confirms
that disbonding depends on the hydrogen content at the
interface.
In table 1, the CHmax values calculated for reactors (operating
conditions are T=450C, pH2=150bar, and the cooling rate is 50C/h),
for different wall thicknesses are given together with the value
obtained for a specimen. For the laboratory test, the exposure
conditions have been taken equal to the reactor service condition
(450C; 150bar H2). CHmax values in laboratory test specimens are
higher than the values obtained for reactor walls. This indicates
that for the cases considered, the disbonding test conditions are
not representative of actual service conditions.
Table 2 gives for each wall thickness, a disbonding test
condition, which would result in the same CHmax value. The
temperature is kept constant, but it is shown that it is necessary
to decrease the hydrogen pressure. The cooling rate has also been
kept constant and equal to 150C/h. In fact for disbonding tests,
the cooling rate must be high enough to limit hydrogen degassing
from the sides of the specimen; 150C/h could be considered as the
minimum cooling rate value to be used. The lower the thickness of
the reactor wall, the lower the hydrogen pressure must be.
In the following, a disbonding test guideline, based on the
actual severity of in service conditions is proposed.
DISBONDING TEST GUIDELINE
Figure 12 gives the amount of disbonding measured by UT on test
specimens, versus the CHmax values calculated for the exposure
conditions used during those tests. The figure gives test results
performed in our laboratory, for many fabricators world-wide. The
results concern different weld overlay procedures, welding
conditions, PWHT While most of the results concern 2.25Cr-1Mo
base
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materials, results for 1.25Cr-0.5Mo and V modified grades
(2.25Cr-1Mo-0.25V and 3Cr-1Mo- 0.25V) are also given. Typical
testing conditions are also reported on the CHmax scale. Testing
conditions 1, 2, 3 and 4 gives CHmax values of respectively 333,
385, 464 and 496ppm.
For 2.25Cr-1Mo, the discrepancy in the result corresponds to the
wide variety of specimens tested: different welding procedure, heat
input, PWHT, base materialHowever it appears that the higher
amounts of disbonded areas correspond to the most severe test
conditions. Below 350ppm, disbonding was never observed on
2.25Cr-1Mo. For CHmax > 500ppm most of the specimens are
disbonded. 1.25Cr-0.5Mo appears more sensitive to disbonding :
Disbonding is observed for a CHmax value of 330ppm. At the opposite
for all the testing conditions, no disbonding has been found with V
modified 2.25Cr 1Mo or 3Cr-1Mo grades, up to CHmax value of 690ppm.
It is necessary to repeat that CHmax has been calculated with
hydrogen diffusivity and solubility laws typical of standard
2.25Cr-1Mo, and that the scale has to be considered as a severity
scale, describing the testing conditions. Due to the increased
hydrogen solubility and lower hydrogen diffusion coefficient for V
modified grades, the actual CHmax value at the interface is well
below the values indicated. It is also possible that the increased
sensitivity with 1.25cr-0.5Mo is linked with lower hydrogen
solubility in this grade. The choice of testing conditions can be
made by comparing the severity scale of the testing conditions with
the severity scale for the service conditions (which take into
account temperature, hydrogen pressure, cooling rate and thickness
of both base material and weld overlay).
Figure 13, is identical to Figure 12, but the CHmax values
calculated for different reactor wall thickness have been reported.
The operating conditions are: 450C and 150 bar H2. A cooling rate
of 50C/h has been chosen for the calculation. This cooling rate can
be considered as an extreme cooling rate for a reactor, so that to
have a conservative approach. The CHmax values obtained for these
conditions are given in Table 1. According to figure 13, for the
overlaying conditions used on 2.25Cr-1Mo, no disbonding is expected
for reactors C, D and E. For reactors B and A, some of the overlay
conditions tested would result in disbonding. If in order to
qualify an overlaying procedure, test condition 3 is selected
(exposure conditions corresponding to in-service conditions), there
is a high probability to have disbonding, but this does not mean
that the quality of the overlay is not acceptable for the service
conditions. For this reason, it is suggested to select the
disbonding test condition, as a function of actual service
conditions.
The proposed approach, is illustrated on Figure 14, for a
temperature of 450C, but such
diagrams can be drawn for other temperatures. On the diagram, a
mapping of CHmax values is given as a function of hydrogen pressure
and thickness. The CHmax values are given for the different
combinations of thickness and pressure. In order to have a
conservative approach, the calculations have been made with a
cooling rate of 50C/h, and an overlay thickness of 4mm. Iso CHmax
curves have been drawn for 450, 400, 300, and 250ppm respectively.
Then domains have been defined, up to 200 bar H2 and up to 350mm
thick reactors. Domain A includes combination of thickness and
pressure giving 480>CHmax > 400ppm, domains B, C, D, and E
correspond respectively to 450/400, 450/350, 350/300 and 300/250ppm
and
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probably possible to consider that combination of operating
conditions which results in less than 300ppm for CHmax will not
result in disbonding, and that tests are not necessary for reactor
operating in domains E and D. For 1.25Cr-0.5Mo probably domain F
will not need disbonding test qualification. For V modified grade
whatever the domain no disbonding is expected, however it can be
suggested to perform disbonding tests for domain A.
CONCLUSIONS
Hydrogen induced disbonding, at the interface between an
austenitic stainless steel weld overlay or cladding and a Cr Mo
base material, is the consequence of strong hydrogen enrichment at
the interface during and after cooling. The influence of in-service
conditions, hydrogen pressure and temperature can be calculated and
then used to determine equivalent test conditions. More severe
service conditions result in higher hydrogen contents. While the
influence of the cooling rate of the vessel does not have a strong
influence on the hydrogen content, it has been shown that the
greater the thickness of the vessel, the greater the amount of
hydrogen at the interface. The use of thick overlays, can be a way
to reduce the hydrogen content. Calculations of hydrogen profiles
in laboratory test specimens show that in most of the cases, use of
actual service conditions, hydrogen pressure and temperature,
results in too severe testing conditions. This is particularly true
for thin reactors. Analysis of many laboratory test results
confirms that in many cases testing conditions used are too severe
and may result in disbonding. An approach has been proposed to
define a disbonding test guideline. Disbonding test conditions have
been proposed. They depend on the severity of the operating
condition of the reactor which take into account the temperature,
the hydrogen pressure and the wall thickness. On the basis of many
test results, it is suggested that disbonding test qualification
may not be necessary for thin reactors or for less severe
in-service conditions, depending on the base material selected.
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REFERENCES
1. H.Okada, K.Naito, J.Watanabe, K.Onishi and R.Chiba: Current
Solutions to Hydrogen Problems in Steels, Ed. C.G. Interrante and
G.M. Pressouyre, ASM 1982, p349
2. M.S. Cayard, R.D. Kane and C.E. Stevens: Paper N518,
CORROSION/94, NACE
international, March 1994.
3. ASTM G146-96: Evaluation of Disbonding of Bimetallic
Stainless Alloy/Steel Plate for Use in High-Pressure, High
Temperature Refinery Hydrogen service, Annual Book of ASTM
Standard, Vol03.02
4. API Recommended practice 934: Materials and Fabrication
Requirements for 2.25Cr-1Mo
and 3Cr-1Mo Steel Heavy Wall Pressure Vessels for High
Temperature, High Pressure Hydrogen Service, First Edition,
December 2000
5. L. Coudreuse: Paper 01533, CORROSION/2001, NACE
International, Houston, march 2001
6. K.Smit and P.F.Ivens: Interaction of Steels with Hydrogen in
Petroleum Industry Pressure
Vessel Service, Ed M.Prager, The Material Properties Council
inc., 1993, p205
7. G.M. Pressouyre, J.M. Chaillet and G.Valette, Current
Solutions to Hydrogen Problems in Steels, Ed. C.G. Interrante and
G.M. Pressouyre, ASM 1982, p331
8. A.Vignes, R.Palengat and P.Bocquet, Interaction of Steels
with Hydrogen in Petroleum
Industry Pressure Vessel Service, Ed M.Prager, The Material
Properties Council inc., 1993, P139
9. L. Coudreuse and P. Bocquet: Hydrogen Transport and Cracking
in Metals, ed A.Turnbull,
The Institute of Materials, 1995, p227
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TABLE 1: Influence of wall thickness on CHmax, comparison with
CHmax for a specimen tested with exposure conditions corresponding
to in service conditions (T=450C ; pH2 =150bar)
Reactor wall
(Cooling rate 50C/h) Specimen
(cooling rate 150C/h) Thickness
(wall+overlay) (mm)
100+6 150+6 200+6 250+6 300+6 40+6
CHmax (ppm) 237 300 338 361 375 462
TABLE 2: Exposure conditions giving same CHmax values than those
obtained for different wall thickness
Thickness (wall+overlay) (mm)
100+6 150+6 200+6 250+6 300+6
CHmax (ppm) 237 300 338 361 375 T (C) 450 450 450 450 450
Cr (C/h) 150 150 150 150 150 Testing
conditions pH2 (bar) 35 58 72 87 95
TABLE 3: Testing conditions suggested for thedifferent domains
of severity described on figure 14
Reactor service conditions Testing specimen thickness (40 +5mm)
Temp (C)
H2max (ppm)
Thickness (mm)
Pressure (bar) Domain Temp (C) Pressure Cr (C/h)
H2max spec
>=450 >=250 >= 170 A 450 150 675 509 >=400 >=180
>= 140 B 450 150 150 475 >=350 >=130 >= 110 C 450 120
150 430 >=300 >=100 >= 80 D 450 90 150 375 >=250
>=80 >= 60 E 450 70 150 335
450C
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FIGURE 1: Typical hydrogen profiles through the wall of a
reactor before and after cooling down
1
Overlay Base Material
Profile before cooling down Profile after cooling down
Ct
Hyd
roge
n
C 0
C 0 1
C 0 2
C t 2
1,00E-04
1,00E-03
1,00E-02
1,00E-01
1,00E+00
1,00E+01
1 1,5 2 2,5 3 3,51000/T
S (p
pm b
ar1/
2 )
450C 25C
Austenitic Stainless Steel
2.25Cr-1Mo
FIGURE 2: Relationship between hydrogen solubility and
temperature (1000/T )
-
1,00E-10
1,00E-09
1,00E-08
1,00E-07
1,00E-06
1,00E-05
1,00E-04
1,00E-03
1 1,5 2 2,5 3 3,51000/T
450C 25C
Austenitic Stainless Steel
2.25Cr-1Mo
D (c
m2 /s
)
FIGURE 3 : Relationship between hydrogen diffusion coefficient
and temperature (1000/T)
a) b)
FIGURE 4: Disbonding test specimens a) parrallelepipedic
specimen 100*50*45
b) ASTM G146 specimen diam 80*45
Austenitic side w elded overlay
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FIGURE 5: Hydrogen distribution in a disbonding test
specimen
1
Overlay Base Material
C 0 C01
C 02
C t 2
Profile before cooling down
Profile after cooling down
Ct
Hyd
roge
n co
ncen
trat
ion
T =425C
100150200250300350400450500
1 10 100 1000
Cooling rate (C/h)
200 bar H2 150 bar H2 100bar H2 50 bar H2
FIGURE 6: Influence of cooling rate and hydrogen pressure on
CHmax
(Thickness 250+6 ; T=425C)
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T =450C
100150200250300350400450500
1 10 100 1000
Cooling rate (C/h)
200 bar H2 150 bar H2 100bar H2 50 bar H2
FIGURE 7: Influence of cooling rate and hydrogen pressure on
CHmax
(Thickness 250+6 ; T=450C)
T =475C
100150200250300350400450500
1 10 100 1000
Cooling rate (C/h)
200 bar H2 150 bar H2 100bar H2 50 bar H2
FIGURE 8: Influence of cooling rate and hydrogen pressure on
CHmax
(Thickness 250+6 ; T=475C)
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T =450C
100150200250300350400450500
0 50 100 150 200 250 300 350 400
wall thickness (mm)
200 bar H2 150 bar H2 100bar H2 50 bar H2
FIGURE 9: Influence of reactor wall thickness on CHmax
(T=450C; tov = 4mm)
INFLUENCE OF OVERLAY THICKNESS (T=450C, pH2 = 150bar))
100150200250300350400450500
0 50 100 150 200 250 300 350 400
wall thickness (mm)
4mm 6mm 8mm
FIGURE 10: Influence of base material and overlay thickness
(T=450C ; pH2 = 150bar)
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0
5
10
15
20
25
200 300 400 500 600 700
CHmax (ppm)
FIGURE 11: Percent of disbonded (D%) area versus CHmax
calculated for
different testing conditions
Weld overlay
0
10
20
30
40
50
60
70
100 200 300 400 500 600 700
CHmax (ppm)
1,25Cr-0,5Mo 2,25Cr-1Mo 3Cr-1Mo 2,25Cr-1Mo-V 3Cr-1Mo-V
4321
Testing conditions1 : 450C - 80bar -100C/h2: 450C - 100bar
-150C/h3: 450C - 150bar -150C/h4: 450C - 150bar -675C/h
FIGURE 12 : Results of disbonding tests performed on weld
overlay, for different testing conditions
-
Weld overlay
0
10
20
30
40
50
60
70
100 200 300 400 500 600 700
CHmax (ppm)
1,25Cr-0,5Mo 2,25Cr-1Mo 3Cr-1Mo 2,25Cr-1Mo-V 3Cr-1Mo-V
4321
Testing conditions1 : 450C - 80bar -100C/h2: 450C - 100bar
-150C/h3: 450C - 150bar -150C/h4: 450C - 150bar -675C/h
Reactor (450C -150bar)Wall thicknessA: 300+6B: 250+6C: 200+6D:
150+6E: 100+6
E CD B A
FIGURE 13 : Comparison of severity of testing conditions with
actual hydrogen content expected in reactor walls
FIGURE 14 : Definition of severity domains as a function of wall
thickness and hydrogen pressure for a temperature of 450C
50
100
150
200
F 81
116
143
169 481472 425 455377298
427418 367 392325257
337330 298 318264208
235231 208 223185146
450 400
350
300
250E
D
C
B A
0 0 50 100 150 200 250 300 350
Wall thickness (mm)
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