Workability assessment of structural steels of power plant units in hydrogen environments
For estimation of hydrogen influence on the workability of high-stressed parts of power plant unit equipment it is necessary to use the crack growth resistance parameters. The new 18Mn-18Cr steel has higher resistance to hydrogen embrittlement and longer residual life time in hydrogen, than the trad...
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| Cite this: | Workability assessment of structural steels of power plant units in hydrogen environments / A.I. Balitskii, V.V. Panasyuk // Проблемы прочности. — 2009. — № 1. — С. 69-75. — Бібліогр.: 11 назв. — англ. |
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| citation_txt | Workability assessment of structural steels of power plant units in hydrogen environments / A.I. Balitskii, V.V. Panasyuk // Проблемы прочности. — 2009. — № 1. — С. 69-75. — Бібліогр.: 11 назв. — англ. |
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| description | For estimation of hydrogen influence on the workability of high-stressed parts of power plant unit equipment it is necessary to use the crack growth resistance parameters. The new 18Mn-18Cr steel has higher resistance to hydrogen embrittlement and longer residual life time in hydrogen, than the traditional 8Mn-8Ni-4Cr steel.
Для оценки влияния водорода на работоспособность высоконапряженных элементов оборудования электростанций необходимо использовать параметры трещиностойкости материала. Показано, что перспективная хромисто-молибденовая сталь 18Mn-18Cr характеризуется более высокими выносливостью и долговечностью в водородной среде, чем традиционно используемая сталь 8Mn-8Ni-4Cr.
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UDC 539.4
Workability Assessment of Structural Steels of Power Plant Units in
Hydrogen Environments
A. I. Balitskii an d V. V. P an asy u k
Karpenko Physico-Mechanical Institute, National Academy of Sciences of Ukraine, Lviv,
Ukraine
For estimation o f hydrogen influence on the workability o f high-stressed parts o f pow er plant unit
equipment it is necessary to use the crack growth resistance parameters. The new 18Mn-18Cr steel
has higher resistance to hydrogen embrittlement and longer residual life time in hydrogen, than the
traditional 8M n-8Ni-4Cr steel.
K e y w o r d s : workability, fracture toughness, hydrogen embrittlement, critical crack
size, durability.
1. C rack In itia tion in M odern Pow er Engineering S tru c tu ra l Com ponents
O p era tin g in G aseous H ydrogen. Energy units and structural components of
fusion power plants (FPP) and nuclear power plants (NPP) operate in contact with
gaseous hydrogen. As example, Fig. 1 shows a typical scheme o f such structural
components. Note that in m odern FPP and NPP there exist hydrogen-producing
devices (electrolyzers, freezers, separators, condensate accumulators, etc.), wide-
branched and long system o f hydrogen pipeline, pumps, system o f cleaning and
drying o f hydrogen. The problem o f workability assessment o f structural steels in
gaseous hydrogen environments is critical for m odern pow er engineering.
Fig. 1. Hydrogen cooling system of modern turboaggregate.
© A. I. BALITSKII, V. V. PANASYUK, 2009
ISSN 0556-171X. Проблемы прочности, 2009, № 1 69
A. I. Balitskii and V. V. Panasyuk
NPP and FPP structural component long-term service in the hydrogen-
containing m edia is shortened by degradation o f physical-mechanical properties
(partially, their embrittlement) [1], decrease o f the resistance o f materials to crack
propagation and plasticity, etc. Some examples o f such degradation are presented
in Fig. 2.
Fig. 2. Hydrogen-induced crack locations in the structural components of modern turboaggregates.
2. F ra c tu re M echanics A pproaches. Development o f the methods and
num erical schemes for material workability estimations taking into account the
above hydrogen degradation o f physical and m echanical properties is very
important. U nder the influence o f various factors, cracks w hich exist in the
structural components o f NPP and FPP propagate during the service.
Crack propagation in the retaining ring or pipe can be estimated by the
fracture mechanics criteria equations for cracked solid bodies [2, 3]:
K Imax( a , O)
K Ic
+ 1
O
I O
= 1, ( 1)
Y /
where O are operation stresses which arise in the pipe (ring) in the crack plane,
K Imax = K Imax(O, a ) is SIF m aximum value for crack with length a in the
cyclic load conditions, O y is the yield strength o f material, and K ic is crack
growth resistance (plane-strain fracture toughness) o f material.
The stress O is defined by the formula:
o =
p R
(2)
where p is pressure, R is inner ring radius, and t is the wall thickness (a < < t).
4 2
t
70 ISSN 0556-171X. npo6n.eMH npounocmu, 2009, N9 1
Workability Assessment o f Structural Steels
For the limit-equilibrium loading 0 = 0 *, we can define the critical crack
size a = a *, achievement o f which results in the spontaneous (catastrophic)
fracture [3] using Eq. (1).
Based on Eqs. (1) and (2), crack value a = a * for particular 0 = 0 * can be
written as
where ^ is a constant which depends on the elastic characteristics o f materials
and body dimensions.
W orkability condition o f a structure w ith a crack-like defect o f size a is
I f macrocracks are detected in a pipeline or ring (Fig. 3), the limit-equilibrium
state of a pipe (ring) under the internal pressure (or under the action of centrifugal
forces) p can be estimated using relations (1)-(3) [3, 4].
Fig. 3. Typical location and character of crack-like defects in the pipelines walls [4].
3. M ethods o f W o rk ab ility A ssessm ent o f C rac k ed M ate ria ls . For
w orkability assessment o f cracked materials or for determination o f plant life
extension it is necessary to establish the tim e o f microcrack, initiation, which
leads to creation o f a m acrocrack w ith m inim al length and period o f its
developm ent [3, 4]. The initial damages are formed via dislocations, chemical
nonregularities and secondary phases precipitations. By nondestructive control
devices (partially by ultrasonic defectoscopy) crack can be detected before the
critical size is reached. Crack critical size is estimated by the methods, which are
based on the fracture mechanics concepts [2, 3], in particular, on the basis o f Eqs.
(1)—(3) and fracture toughness values (crack resistance K Ic).
The data on variation o f fracture toughness and other characteristics of
material in hydrogen-containing environments are very important.
Experimental investigation has been perform ed in the Karpenko Physico-
Mechanical Institute o f the National Academy o f Sciences o f Ukraine. Dimensions
o f tested specimens are shown in Fig. 4a. Variation o f such physical-mechanical
a * = ^ (3)
a < a *. (4)
ISSN 0556-171X. npoôëeMbi npounocmu, 2009, N 1 71
A. I. Balitskii and V. V. Panasyuk
characteristics as E (the Young modulus), d , p (macrodeformations), K Ic
(fracture toughness) for power engineering purposes in dry air (A) and hydrogen
(H ) have been studied and the following results were obtained [6 , 7] (see Table 1).
Young’s modulus practically did not change, but fracture toughness changed
drastically (in hydrogen-containing environment it decreased). It is known from
[5] that the values decrease w ith the service time or under the hydrogen action
due to m aterial embrittlement.
T a b l e 1
Physical and Mechanical Characteristics of Steels for Retaining Rings Units
of Turbogenerator in Air (A) and in Hydrogen (H)
Steel E,
GPa
O u ■.
MPa
OY ■.
MPa
ô ,% ■ % KIc ■
MPaVm
8Mn-8Ni-4Cr 189 (A) 1157 (A) 925 (A) 30 (A) 60 (A) 200 (A)
185 (H) 1002 (H) 800 (H) 22 (H) 55 (H) 160 (H)
18Mn-18Cr 200 (A) 1197 (A) 1136 (A) 29 (A) 64 (A) 268 (A)
197 (H) 1152 (H) 1121 (H) 21 (H) 60 (H) 224 (H)
a b
Fig. 4. Specimen dimensions and crack orientation for crack resistance parameters’ dertermination (a)
in the retaining ring wall of turbogenerator (TG) rotor made of the 8Mn-8Ni-4Cr and 18Mn-18Cr
steels and service stresses which are applied to crack-like defects (b).
Assume that Young’s modulus do not change in hydrogen-containing
environment, while fracture toughness varies. In a such case, coefficient ^ in the
formula (3) can be assumed independent o f environment (^ H = ^ a )■
Then the critical crack size during the materials service in hydrogen (H ) and
air (A ) is determined by formulas:
H K Ic(H )
a H (5)
O *( H )
A K Ic(A ) _
a * = n ~ -----■ (6)
O *(A )
72 ISSN 0556-171X. npoôëeMbi npounocmu, 2009, N9 1
Workability Assessment o f Structural Steels
On the basis o f formulas (5) and (6), we obtained
K lc(H )
a *(h) - a *(A ) 2 ■ (7)
K Ic(A )
Exactly the same approaches are used in some normative documents [8 , 9].
Take into account, that in some cases m aterial embrittlement after long-term
service (30-40 years) leads to formation o f smaller cracks, than predicted by
formula (7).
This fact is attributed to calculation errors o f coefficient K i ( a , o ), or with
phenom ena ofl additional ageing o f materials (additional decrease o f material
fracture toughness during long-term operation in service environment) [5, 10]. In
this respect, the problem requires additional investigation.
4. A ccount o f S ubcritica l C rac k P ropaga tion . Retaining ring workability
assessment perform ed according to normative documents [8 , 9] takes into account
the existence (extreme case) o f a surface defect, w hich is treated as a plane
semielliptical crack w ith axes a and l , where a is a smaller semiaxis which
coincides with crack propagation direction to the depth o f the retaining ring wall
and characterizes the crack depth, and l is a larger semiaxis which is fixed on the
ring surface (see Fig. 3). The m ost frequent are the following axis relations
a — (0.15-0.35)l. These relations were established as a results o f retaining rings
service inspection during long-term operation (Table 2) [1, 5]. The critical crack
sizes are established by formula (7) according to the normative documents of
pow er engineering industry [8 , 9].
T a b l e 2
Parameters of the Service Defects of Retaining Rings Made of 8Mn-8Ni-4Cr Steel
TG type Depth
(small semiaxis, Fig. 3)
of semielliptical
crack a, mm
Length
(large semiaxis, Fig. 3)
of semielliptical
crack l , mm
Durability
W ,
cycles
nj , starts
(cold
state)
ni , starts
(hot
state)
TGV-200 0.5-5.0 1.5-35.0 9.7-109 65 45
10.0-15.0 28.0-100.0 8.6 • 107 51 29
TGV-300 0.5-5.0 0.5-5.0 1.1-1010 55 40
10.0-15.0 28.0-100.0 9.0-107 48 29
For definition o f the critical m om ent o f state, which prevents fracture
(durability closing) o f retaining ring unit the stress intensity factor (SIF) at
plane-strain fracture K i ( a , o ) is used. The critical state is considered such, when
the m aximum SIF value on the crack contour achieves the fracture toughness K i c.
Using Life Assessm ent Code EPRI IN-103088, IN-1030887 for life
prediction o f the retaining ring w ith defects, we obtain that for the crack depth
a * — 24 mm the fracture o f retaining ring made from steel 18M n-18Cr takes
place after 5 thousand hours o f operation [10, 11]. However, the hydrogen factor
ISSN 0556-171X. npodxeMbi npounocmu, 2009, N 1 73
can decrease drastically at that time, since the critical crack size in gaseous
hydrogen is lower [see Eq. (7)]. Thus, it is necessary to take into account the real
value o f K lc(H ) for working environment.
A ssessm ent o f m odern steels has shown that high nitrogen-containing
18M n-18Cr steel with higher value o f fracture toughness (see Table 1) provides
safe carrying ability o f cracked retaining ring during longer operation time in
hydrogen environment than conventional 8M n-8N i-4C r steel [10, 11].
A. I. Balitskii and V. V. Panasyuk
a b
Fig. 5. (a) Dependence of the crack growth propagation rate on SIF in high-strength 8Mn-8Ni-4Cr
steel:(1) in air with 15% humidity, T = 20°C; (2) in hydrogen with 15% humidity, T = 20°C; (3) in
hydrogen with 40% humidity, T = 20° C; (4) in air with 90% humidity, T = 65°C; (5) in hydrogen
with 90% humidity, T = 65°C; (6) under electrolytic hydrogenation with current density 1 A/dm2.
(b) Working environments can greatly accelerate the growth rates of SCC in steel 18Mn-18Cr:
SCC growth rates estimated by dividing the total crack depth by the total service time of the
damaged generator rotor retaining rings: FPP Perm-1 (PI), Perm-II (PII), Perm-III (PIII), Rjazan
(R), Porto-Tolle (PT), Burshtyn-11 (B11) (8Mn-8Ni-4Cr), Gacko1 in gaseous hydrogen, pure water
and in 22% NaCl solution [1, 5].
As a result o f the analysis o f cracks detected at the Burshtyn 11 FPP TG
retaining rings (Fig. 5) it is established that crack propagation rates are
commensurable with crack rates, obtained during experimental testing o f specimens
m ade o f 8M n-8N i-4C r steel in hydrogen-containing environments. Crack rates in
18M n-18Cr steel retaining rings at the Perm FPP are equal to 0 .10-7.0 m m /year
and are lower than those in the retaining rings made o f 8M n-8N i-4C r steel (Fig. 5).
C o n c l u s i o n s
1. For estimation o f hydrogen influence on the workability and residual life
time o f high-stressed parts o f pow er engineering equipment it is necessary to use
the crack growth resistance parameters (fracture toughness, crack-like defects
critical sizes) and their values in the initial and deteriorated states.
2. During operation in hydrogen, the high nitrogen-containing 18M n-18Cr
steel has a higher resistance to hydrogen em brittlement and to stress corrosion
cracking, than traditionally used nitrogen-containing 8M n-8N i-4C r steel.
74 ISSN 0556-171X. npo6n.eMH npounocmu, 2009, N 1
Workability Assessment o f Structural Steels
1. V. V. Panasyuk (Ed.), F r a c tu r e M e c h a n ic s a n d S tr e n g th o f M a te r ia ls :
R e fe r e n c e B o o k , Vol. 8 : A. I. Balitskii (Ed.), S tre n g th o f M a te r ia ls a n d
D u r a b il i ty o f S tr u c tu r a l E le m e n ts o f N u c le a r P o w e r P la n ts [in Ukrainian],
PH “Akadem periodyka,” Kyiv (2005).
2. A. Neimitz, O cen a W y trzy m a lo sc i E le m e n to w K o n stru k c y jn y c h Z a w ie ra ja c y c h
P e k n ie c i a ( P o d s t a w o w e E le m e n ty P r o c e d u r S I N T A P ) , P o litech n ik a
Swietokrzyska, Kielce (2004).
3. V. V. Panasyuk, S tre n g th a n d F r a c tu r e o f S o lid s w ith C ra c k s [in Ukrainian],
National Academ y o f Sciences o f Ukraine, Karpenko Physico-M echanical
Institute, Lviv (2002).
4. V. V. Panasyuk (Ed.), F r a c tu r e M e c h a n ic s a n d S tr e n g th o f M a te r ia ls :
R e fe r e n c e B o o k , Vol. 7: I. M. Dmytrakh (Ed.), R e lia b il i ty a n d D u r a b il i ty o f
S tr u c tu r a l E le m e n ts f o r H e a t - a n d - P o w e r E n g in e e r in g E q u ip m e n t [in
Ukrainian], PH “Akadem periodyka,” Kyiv (2005).
5. R. Grudeli, C. Rinaldi, L. Rossi, et al., “A case history o f a 18M n-18Cr
retaining ring affected by stress corrosion cracks after 33500 operation
hours,” in: M o to r & G e n e r a to r P r e d ic t iv e M a in te n a n c e & R e fu rb ish m e n t
(Proc. CIGRE/EPRI 1997 Europ. Colloq.), Florence, Italy (1997), p. 5.
6 . V. I. Tkachov, V. I. Kholodnyi, I. N. Levina, W o r k a b ili ty o f S te e ls a n d
A llo y s in H y d r o g e n E n v iro n m e n ts [in Ukrainian], National Academ y of
Sciences o f Ukraine, Karpenko Physico-M echanical Institute, Lviv (1999).
7. A. I. Balitskii, “Increasing o f exploitation characteristic o f high-nitrogen
C r-M n steels,” in: H ig h N itr o g e n S te e l , ETH, VDF, Zurich (2003), pp.
323-331.
8 . O. S. Loshak, A. I. Balitskii, L. G. Pulkas, et al., Methodical Recommendations
o f Technical State Evaluation o f Turbogenerator Rotor Retaining Rings
(Normative Document SNOU-N EE 45.301:2006) [in Ukrainian], Ministry
o f Fuel and Energetic o f Ukraine, Decision o f M inister No. 432, GRIFRE,
Kyiv (2006).
9. O. S. Loshak, A. I. Balitskii, L. G. Pulkas, et al., M e th o d ic a l R eco m m en d a tio n s
o f T e c h n ic a l S ta te D ia g n o s t ic a n d E v a lu a tio n o f L ife T im e o f S te a m T u rb in e
C a s t V e sse l D e ta i l s (N o rm a tiv e D o c u m e n t S N O U -N E E 3 0 .3 0 4 :2 0 0 7 ) [in
Ukrainian], M inistry o f Fuel and Energetic o f Ukraine, Decision o f M inister
No. 124, GRIFRE, Kyiv (2007).
10. R ec o m m e n d a tio n f o r S tr e s s C o rro s io n T e s tin g U sin g P r e -C r a c k e d S p ec im en s,
ESIS-Procedures, P 4 -92 D (1992).
11. A. Balitskii, “Reliability and durability assessment o f structural materials for
NPP using fracture mechanics approaches,” Z e s z y ty N a u k o v e P o lite c h n ik i
O p o lsk ie j, Ser.: M e c h a n ik a , z. 79, N r kol. 300 (2005), ss. 33-52.
Received 11. 06. 2008
ISSN 0556-171X. npoöxeMbi npounocmu, 2009, N 1 75
|
| id | nasplib_isofts_kiev_ua-123456789-48474 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 0556-171X |
| language | English |
| last_indexed | 2025-12-07T17:16:25Z |
| publishDate | 2009 |
| publisher | Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| record_format | dspace |
| spelling | Balitskii, A.I. Panasyuk, V.V. 2013-08-20T04:16:40Z 2013-08-20T04:16:40Z 2009 Workability assessment of structural steels of power plant units in hydrogen environments / A.I. Balitskii, V.V. Panasyuk // Проблемы прочности. — 2009. — № 1. — С. 69-75. — Бібліогр.: 11 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48474 539.4 For estimation of hydrogen influence on the workability of high-stressed parts of power plant unit equipment it is necessary to use the crack growth resistance parameters. The new 18Mn-18Cr steel has higher resistance to hydrogen embrittlement and longer residual life time in hydrogen, than the traditional 8Mn-8Ni-4Cr steel. Для оценки влияния водорода на работоспособность высоконапряженных элементов оборудования электростанций необходимо использовать параметры трещиностойкости материала. Показано, что перспективная хромисто-молибденовая сталь 18Mn-18Cr характеризуется более высокими выносливостью и долговечностью в водородной среде, чем традиционно используемая сталь 8Mn-8Ni-4Cr. en Інститут проблем міцності ім. Г.С. Писаренко НАН України Проблемы прочности Научно-технический раздел Workability assessment of structural steels of power plant units in hydrogen environments Оценка работоспособности конструкционных сталей в элементах тепловых и атомных электростанций, работающих в водородных средах Article published earlier |
| spellingShingle | Workability assessment of structural steels of power plant units in hydrogen environments Balitskii, A.I. Panasyuk, V.V. Научно-технический раздел |
| title | Workability assessment of structural steels of power plant units in hydrogen environments |
| title_alt | Оценка работоспособности конструкционных сталей в элементах тепловых и атомных электростанций, работающих в водородных средах |
| title_full | Workability assessment of structural steels of power plant units in hydrogen environments |
| title_fullStr | Workability assessment of structural steels of power plant units in hydrogen environments |
| title_full_unstemmed | Workability assessment of structural steels of power plant units in hydrogen environments |
| title_short | Workability assessment of structural steels of power plant units in hydrogen environments |
| title_sort | workability assessment of structural steels of power plant units in hydrogen environments |
| topic | Научно-технический раздел |
| topic_facet | Научно-технический раздел |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/48474 |
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