damage due to hydrogen embrittlement and stress...

Damage due to hydrogen embrittlement and stresscorrosion cracking

Jarmila Woodtli, Rolf Kieselbach*

EMPA, Uberlandstrasse 129, CH-8600 Dubensorf, Switzerland

Received 3 September 1999; accepted 20 September 1999

Abstract

Damage of metals due to the in¯uence of hydrogen and to stress corrosion cracking is quite frequent and leads todangerous failures as well as to loss of property and large compensational payments by insurance companies. One

reason for this, is that some designers and engineers seem to lack su�cient knowledge of the basic mechanisms ofthese phenomena and accordingly often have only vague ideas how to prevent such failure causes. Although thebasic concepts can be found in a number of good text books it seems worthwile to recall them in a short

comprehensive paper. 7 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Embrittlement; Environmental interaction; Hydrogen-assisted cracking; Stress corrosion cracking

1. Introduction

A previous survey [1] has shown that approximately one third of all failure cases are caused byenvironmental e�ects like corrosion. This failure cause means more than simple rusting of iron and steelas is shown in this paper. Whereas this kind of corrosion is visible and thus can be easily detected, thedamage caused by the phenomena discussed in this paper is normally invisible and unforeseeable andtherefore much more dangerous.

A ®rst example is the failure of a storage tank for compressed hydrogen. The consequences of this canbe ascertained from Fig. 1. This failure was caused by the growth of large fatigue cracks which wasinduced by hydrogen in¯uence. The total damage paid by insurance in this case was approximatelyUS$50 million. Hydrogen damage is more frequent than many people would suspect.

Another important source of failure is stress corrosion. In this failure mechanism the damage isproduced by simultaneous action of stress, corrosive substance and the properties of the material. An

Engineering Failure Analysis 7 (2000) 427±450

1350-6307/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved.

PII: S1350-6307(99 )00033-3

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* Corresponding author. Tel.: +41-1-823-5511; fax: +41-1-823-4014.

E-mail address: [email protected] (R. Kieselbach).

example of a failure caused by stress corrosion cracking was the accident at the Uster indoor swimmingpool in Switzerland. There, a dead concrete ceiling had been suspended over the pool by a great numberof bars made from stainless steel (AISI 304, DIN 1.4301). After several years' service some of these barsbroke, the roof collapsed and 15 swimmers were killed. The investigation showed that the stainless steelhad been severely corroded (Fig. 2).

By detailed metallurgical tests it was proven that the failure had been brought about by stresscorrosion cracking. A typical indication for this kind of damage is the branched cracks of Fig. 3.

Material damage due to hydrogen embrittlement and stress corrosion cracking can be classed as caseswhich cannot be clari®ed based on mechanical parameters alone. Both types of damage are caused bythe ambient medium and are therefore controlled by physical, chemical or electromechanical processes.The appearance of the damage is also similar: in both cases delayed low ductility fractures or cracksappear and the material is embrittled only locally in locations where contact has occurred with thedamaging medium. The role of hydrogen in the mechanism of stress corrosion cracking has been knownsince the 1970s so that preventative measures have since been introduced. Although hydrogen-inducedcracking and stress corrosion cracking are similar phenomena, both types of damage are usuallydescribed and treated separately. The reason for this is the complexity of the damage mechanism whichis dependent on the particular material and damaging medium. In some cases a combination of bothmechanisms can be found which is then called hydrogen-induced stress corrosion cracking. Thefollowing paragraphs deal with this subject from a failure analysis point of view.

2. Hydrogen damage

2.1. General aspects

Hydrogen embrittlement is usually understood as the unwanted delayed brittleness of a material

Fig. 1. Factory after rupture and explosion of a storage tank for hydrogen.

J. Woodtli, R. Kieselbach / Engineering Failure Analysis 7 (2000) 427±450428

Fig. 2. Fracture surface of broken hanger of dead concrete roof, made from stainless steel.

Fig. 3. Branched cracks of stainless steel bar of Fig. 2.

J. Woodtli, R. Kieselbach / Engineering Failure Analysis 7 (2000) 427±450 429

which is caused by the presence of hydrogen within the material. Practically all metal materials can bedamaged by the absorption of hydrogen, if a su�cient quantity can penetrate into the material. Thesources of the hydrogen, the paths it takes to enter the material and the embrittlement mechanisms areextremely diverse. These factors must therefore be established in each particular case. Only then canpreventative measures be taken at the correct location or during the correct stage of a process.

The aim of this paper is to explain both the embrittlement mechanisms and the characteristic visibleforms of the damage. These are illustrated by individual examples. For the failure analysis and theresulting preventative measures the following aspects of hydrogen embrittlement need to be understood:

. the source of the hydrogen;

. the absorption of the hydrogen into the metal;

. transport processes;

. the embrittlement mechanism and visual appearance.

2.2. Source of the hydrogen

Hydrogen always enters metals as exogenous contamination. A component or system can becontaminated by hydrogen in various stages of its useful life. This begins in the metallurgical process [4],because the hydrogen solubility in the molten metal is much higher than when it is in the solid condition(see Fig. 4). This hydrogen loading is reversible to a great extent, because it is caused mainly by thestorage of the hydrogen in the interstitial positions of the lattice. Irreversible damage only occurs if thehydrogen can e�use or if it can accumulate as gas in the hollow spaces. This type of hydrogen damageis of importance in welding practice and is exhibited for instance in the development of cold cracks or®sh eyes (or ¯akes). This type of damage is also produced during casting.

Another source of hydrogen during the manufacturing process is the galvanising process or ¯ashpickling. The hydrogen is produced by the cathodic partial reaction of the electromechanical processeswhich is why the damage caused is designated as electromechanical induced hydrogen cracking. At ®rstthe hydrogen di�uses in the material (Fig. 5) and is then taken up into traps. In relatively soft steel oraluminium alloys, the hydrogen can recombine to form gas molecules on internal defects such as non-metallic inclusions. Due to the high gas pressure [2] separations are produced parallel to the surface(bubble formation).

In Fig. 6 the fracture surface of a tensile specimen is illustrated in which a large number of ®sh eyescan be detected. The fracture happened during a tensile test which had a reduced tensile strength from487 to 529 N/mm2 (speci®ed value: 540 N/mm2) (Fig. 7). The hydrogen, which can be recognisedfractographically from the cleavage aureole around the pores and the non-metallic inclusions, originatedfrom humid feed material or badly dried oven lining. The greater the number of pores within thecasting, the greater the amount of enclosed hydrogen (see Fig. 8).

This type of hydrogen embrittlement is also called internal hydrogen embrittlement and is explained bythe pressure theory based on thermodynamic principles. The equation for the balance between theatomic and gaseous hydrogen is:

cH � 135��pH2

p ÿ 6500=RT, �1�where cH is the hydrogen concentration in ppm and pH2

the hydrogen pressure in MPa in the solidphase of the adjacent gas phase. R is the gas constant and T is the absolute temperature. Accordingly, 1ppm of dissolved hydrogen is balanced by gaseous hydrogen at room temperature and at a pressure of 2� 105 MPa. The embrittlement is due to the fact that the excess dissolved hydrogen disperses intoinclusions, pores or microcracks and, because of the high pressure (e.g. in the form of blistering ¯akes)


or under external forces, results in cracks to the lattice. Even when it is considered that for kineticreasons the actual pressures reached are one or two times lower, there would still be considerablepressure which could have an impact on the lattice.

High tensile strength and cold drawn steels with apparent elasticity limits exceeding 650 N/mm2 are atparticular risk. The embrittlement is approximately proportional to the logarithm of the hardness and inaddition is related to the value of the di�usion coe�cient for hydrogen (see Fig. 9) [3].

Martensitic structures are considerably more susceptible than bainitic structures, ferrite, austenite orprecipitation-hardened steels. Moreover, coarse grained materials are more susceptible to brittleness than®ne. In steel, the di�usible hydrogen should be forced out during the surface treatment between 190 and2208C [9] because the e�usion rate is far too low at room temperature (see Fig. 10).

Fig. 4. Solubility of hydrogen in iron as a function of temperature and of pressure.


Fig. 5. Coe�cient of di�usion for hydrogen in ferrite (F) and austenite (A) respectively; Lattice di�usion (G) [3].


Fig. 11 shows blistering phenomena on a galvanised steel surface (unalloyed carbon steel tempered to460 HV5). Apparently these washers were not fully degassed. They failed after a relatively short time inoperation due to low ductility cracks and fractures even though the load at a torque of 70 Nm was very low.

Fig. 6. Fish eyes on the fracture surface.

Fig. 7. Cleavage fracture of the aureole of a ®sh eye region.


The fracture surface (Fig. 12) indicates typical characteristics of hydrogen embrittlement in the formof a partially intercrystalline fracture with ductile markings on the grain boundaries (crow's feet). Thisfracture pattern may be a typical indication but it is nevertheless not a satisfactory proof of hydrogenembrittlement. In this particular case the residual hydrogen content of up to 1.49 ppm was determinedby a gas chromatograph. This hydrogen concentration was above the lower brittleness threshold whichlies between 0.3 and 3 ppm due to the particular material [5].

In general the contact between hydrogen gas and a steel surface at room temperature cannot beconsidered as a problem. On the one hand the dissociation constant of hydrogen at room temperature isvery high (429.5 kJ/mol), and on the other hand the di�usion coe�cient of 1.5 � 108 is very low (seeFig. 5 [3]). Therefore for almost 100 years containers, reactor tanks and gas bottles made of steel havebeen used successfully for the transport of hydrogen. Nevertheless the formation of cracks is possible,especially due to the combined impact of mechanical stress concentration and hydrogen dissociation.

Fig. 8. Solubility of hydrogen in iron having di�erent porosities at di�erent temperatures and pressures.


The high dissociation energy of the hydrogen is applied by a deforming metal surface. For this reasonthe hydrogen in a tension or ductile ®eld can penetrate into the metal lattice much more easily than intoan intact tension-free surface, even if only microscopically. Therefore the atomic hydrogen di�usespreferably on notched locations and crack openings with a three axis tension distribution and causesdecohesion of the lattice. Especially in high-tensile steel, high crack propagation rates can occur (seeFig. 13).

When the hydrogen is under pressure, the crack propagation rate is higher by a factor of 2 [6]. H2Scan also cause an increase in the crack propagation rate [7]. At temperatures above 3008C the partialpressure is the decisive factor for the impact of the hydrogen (see Fig. 14).

Above 3008C the hydrogen solubility in steel follows the Sievert law:

cH � kT ��PH2

p �2�The Arrhenius equation kT � k0 � exp�ÿQ=RT � can be used to determine kT, where Q is the heat ofsolution of 27.2 kJ/mol.

In addition at this temperature there is no longer a problem of the high energy threshold for the

Fig. 9. Coe�cient of di�usion for hydrogen in di�erently structured steels built up during hydrogen loading (solid line), e�usion

(dotted line). At right: time of di�usion for a length of 1 cm �l � ��D � tp � [3].


dissociation, adsorption and absorption of the hydrogen. After di�usion of the hydrogen the damage atincreased temperatures, however, is not caused by the material embrittlement but by the structurechanges in the material. In carbon steels the combined carbon reacts as Fe3C with the hydrogen andforms methane. The steel loses its strength due to decarburization. The resistance to the formation ofmethane can be improved by suitable alloying additions or carbide components such as Cr, Mo, V, Wor by using austenitic steels.

3. Stress corrosion cracking

Stress corrosion cracking is understood as the formation of cracks in metals with simultaneous impactof certain corrosive media and tensile stress. Stress corrosion cracking does not only cause low ductilityfractures in high tensile materials but also in ductile materials. In all cases of stress corrosion crackingthree parameters with synergy impact are involved:

. material

. medium and

. mechanical loading

Fig. 10. Di�usion of hydrogen after loading for 80 h in a saturated solution of H2S at room temperature.


Fig. 11. Opened bubble on a galvanised steel surface.

Fig. 12. Partially intercrystalline fracture with ductile marks on the grain-faces.


Fig. 13. In¯uence of hydrogen on the crack growth rate of a low alloy steel.


Fig. 14. In¯uence of hydrogen pressure and temperature on the onset of damage by CIW [8].

Table 1

Some examples for stress corrosion cracking [21]

Material Medium Remarks

Low alloy

ferritic steels

Alkaline liquids (caustic solutions,

carbonate and bicarbonate solutions)

Among other things, so-called ``caustic embrittlement''. Precise

composition and heat treatment of material as well as temperature and

concentration of the solution are important

Nitrate solutions As above. Test in a boiling standardised (DIN 50915) water and Ca

(NO3)2ÿ solution as test for susceptibility to intercrystalline SSC

High alloy

austentite

steels

Chloride solutions Min. temperature of approximately 608C usually required,

transcrystalline crack formation

Caustic alkali solutions Trans- or intercrystalline crack formation dependent on the

electrochemical potential, concentration, heat treatment, etc.

Oxidised high temperature water Intercrystaline crack formation on sensitised material (chrome depletion:

intercryst. without tensile stress in Strauss test)

Nickel-based

alloys

Caustic alkali solutions Trans- or intercrystalline cracking depending on material (or condition)

electrochemical potential, concentration, etc.

Pure high temperature water ``Coriou'' e�ect; dependent on material, long incubation time, crack

conditions have a negative e�ect

Copper-based

alloys

Ammonia solution, nitrate solutions Composition of the solutions is critical

Aluminium-

based alloys

In particular solutions containing

halogen

Intercrystalline crack formation, composition and heat treatment of the

material is important

Titanium-

based alloys

Aqueous solutions containing chloride Crack formation often only when sharp notches are present


Each of these parameters must be considered individually; therefore with respect to stress corrosioncracking, a material cannot be characterised solely on the basis of its chemical composition but also byits condition caused by heat treatment (see Table 1).

In order to be able to classify the wide range of damage mechanisms, it is advisable to di�erentiatebetween cathodic, anodic and expansion-induced crack formations. According to its particularmechanism, cathodic stress corrosion cracking can be classi®ed within the range of hydrogenembrittlement, as already discussed in Section 2.2.

3.1. Anodic stress corrosion cracking

Anodic stress corrosion is selective. It occurs only in the passive condition of the material, i.e. whenthe metal surface is covered by a passive or protective layer. Most model concepts assume that anaccelerated anodic disintegration of metal takes place on a crack tip kept free from protective layers bychemical and mechanical e�ects (see Fig. 15) [15]. According to this theory the freshly created crackedge must be immediately re-protected by the formation of passive or covering layers because otherwisecrack fatigue could occur. In this way stress corrosion cracking spreads through the material like an``electromechanical knife''. A general con®rmation of this concept is demonstrated by Parkin's theory(see Fig. 16) [16].

Fig. 15. Mechanism of common SCC by anodic solution.


According to this theory, the growth rates of stress corrosion cracks have a strong interrelation to themeasured peak current densities with the anodic disintegration of various material/corrosion mediumcombinations.

Intercrystalline stress corrosion cracking occurs in passivatable materials, for instance sensitisedstainless steels, certain aluminium alloys and C steels in oxidised media (see Table 1) [21]. This corrosionoccurs only in a limited potential range. Due to enriched impurities, the grain boundary needs a higherpassivation current density than the internal grain. In addition the breakdown potential of the grainboundary is reached earlier than that of the internal grain. In this connection, mechanical tensile stressesplay an important role. On the one hand they cause mechanical cracking of the grain boundary regionand on the other hand they reduce the breakdown potential and thus make corrosion possible. Theprogress of intercrystalline stress cracking is therefore independent of the e�ects of mechanical stress.For this reason the residual tensile stresses located only on the outermost surface of a component aresu�cient to initiate stress corrosion cracking.

Fig. 16. Velocity of SCC and maximal current density [17].


The large number of models written for transcrystalline stress corrosion cracks place emphasis eitheron the electromechanical or the physical metal mechanisms. The ®lm breakdown theory is based on therepeating sequence of the formation and destruction of the outer layers which is made possible by thegliding planes on the top surface. This process can be accelerated by the formation of elements betweenthe passive walls of the crack and the active base of the crack (see Fig. 17) [18].

According to the tunnel theory, as a result of the interaction of a sliding band with passive layer,tunnel shaped pitting is produced which expands sideways under mechanical stress and later forms afeathery fracture structure (see Fig. 18).

The appearance of stress corrosion cracking can be demonstrated by damage to components made ofa+b brass. At the beginning of this century the phenomenon of stress corrosion cracking was observedon copper based alloys. The aggressive impact of ammonia, together with its compounds andderivatives, was very soon recognised [19]. In the recent past, cases of damage caused by the impact ofindustrial atmospheres have increased [20] which have also been shown by long-term outdoorinvestigations. For instance cold worked samples made of brass CuZn37 with various stress relievinganneal treatments indicate that SSC can still occur after a long incubation period dependent on ambientconditions and due to the very low internal tensile stress [22].

Fig. 17. Mechanism of the theory of ®lm breaking for SCC.


Fig. 18. Mechanism of the tunnel theory for SCC.


Figs. 19 and 20 show plumbing parts damaged on the basis of crack formation in the lengthwaysand transverse directions. The fractographic investigations indicated an intercrystalline fractureprogression (Figs. 21 and 22). A branched crack progression and a perfect microstructure consistingof a+b mixed crystals was discovered on the metallic microsections including the fracture area.Extreme cold formings on the thread ¯anks, which would have indicated an installation error, werenot present. The blue colouring of the fracture surfaces as well as the proof of nitrogenatedcompounds on the fracture surfaces indicate that SCC had been triggered by ammonia or itscompounds with the additional impact of moisture. In this particular case the mechanical stresses thattriggered the fractures can be considered as low tensile stresses which are unavoidable duringinstallation work. The tap extension with the transition of the cross-section also indicates a locationwith stress concentration. The modi®cation to the design (Fig. 19(D)) should help to reduce the stresspeaks on the transition of the cross-section.

3.2. Strain-induced corrosion cracking

The material and the corrosive medium are the decisive factors for conventional SCC. In contrastto this, for strain-controlled corrosion cracking, the mechanical load is a more central factor. Thestress can be static but also cyclic. When the load frequency is high, the damage is caused by fatiguecorrosion cracking. Strain-induced corrosion cracking occurs especially in alternating operatingconditions. Bead chain type cracks are formed when repeated changes occur between corrosionprocesses caused during stationary conditions and mechanical loads in normal operation during which

Fig. 19. Faucet extension made from brass showing fracture (A), (B) and cracking (C).


mechanical destruction of the top layer is produced. Magnetite layers on pipe bends and tube platesin hot water systems can be mentioned as examples. Thermal dilatation of the component is su�cientas the mechanical load.

Fig. 21. Microstructure of a+b-brass with branched cracks.

Fig. 20. Longitudinal crack in brass ®tting.


3.3. Hydrogen-induced stress corrosion cracking (HISCC)

This type of damage is a transition form between the classical hydrogen embrittlement and stresscorrosion cracking and applies in particular to high-tensile steel in low aggressive water solutions,austentitic steel in diluted sulphuric acid, alloys in halogenide solutions and uranium alloys in watersolutions [10].

When a building component or system is subjected to corrosion created by the development ofhydrogen, the cathodically isolated hydrogen di�uses into the material and causes local embrittlement.The hydrogen develops either in oxygen-free, neutral or alkaline mediums by the reduction of watermolecules

2H2O� 2eÿ � 2OHÿ � 2H� �3�or as a result of hydrolysis of corrosion products (in pitting locations, narrow cracks), for instance:

3Fe2�4H2O � Fe3O4 � 8H� � 2eÿ

2H� � 2eÿ � 2Had �4�

In acid solutions (pH < 4) the protons H+ are reduced to H2. In general, acid corrosion of steel indiluted halogenide solutions emanates from an acid corrosion mechanism in narrow gaps [11]. Thedi�usion processes cause increased concentrations of halogenide and metal ions inside the cracks and,due to hydrolysis (Eq. (4)), the pH value in the crack sinks [10]. In addition, a decrease in the potentialindependent of the external polarisation can be detected in the narrow cracks and splits. This is caused

Fig. 22. Intercrystalline fracture surface.


by the development of H2 gas bubbles which leads to the production of a ``short circuit cell'' at thecrack opening which to a great extent is decoupled from the surface. In English technical literature theexpression ``occluded corrosion cell'' is used [12].

Molecular hydrogen is less damaging for steel than atomic hydrogen due to its high dissociationconstant at room temperature. When kinetic inhibition of recombination exists, as is the case with thepresence of, for instance, sulphides, arsenic, selenium and phosphorus compounds, considerable partialpressures can occur due to the accumulation of adsorbed hydrogen atoms on the surface. Theinterstitially dissolved hydrogen is particularly mobile in steel. The di�usion coe�cient of steel isbetween 10ÿ4 and 10ÿ5 cm2/s [13] which is comparable with di�usion coe�cients in ¯uids. Therefore assoon as the hydrogen has penetrated through the phase boundary into the metal, it is capable ofpenetrating to a depth of 100 mm into the material [14]. Thus a lattice deformation take place and alsoan accumulation of hydrogen on the boundary surfaces (e.g. at grain boundaries, pores and inclusions).

It can be proved [15] that, with the increasing strength of the steel, a notched sample subjected tohomogeneous hydrogen produces inhomogeneous distribution of the hydrogen. The hydrogen isconcentrated in the range of the maximum hydrostatic stress in the ligament. If at ®rst the material ishydrogen-free, for the same reason, the hydrogen absorbed on the crack edges is distributed selectivelyinto the crack ligament (see Fig. 23). In this case the corrosive hydrogen is concentrated where the mostdamage exists, which is in cracks, notches or other material defects that cause an increase in stress.Therefore this type of material damage should not be considered as global but as very local hydrogenembrittlement.

A special type of this category of damage occurs with welded high tensile ®ne grained steel in fullydemineralised or boiler feed water. At temperatures between 50 and 2508C a magnetite layer is created

Fig. 23. Hydrogen di�usion in a stressed specimen at externally (a) or internally (b) supplied hydrogen. The normal stress syy in

the ligament and the crack opening displacement CTOD is shown on top.


(Schikorr reaction) caused by the development of hydrogen. After a long incubation time, cracks canoccur in the heat a�ected hard zones of the weld joint, when they are not subjected to stress relief heattreatment.

An example of hydrogen induced stress corrosion cracking is shown in Figs. 24±26. The shaft madeof alloyed tempering steel ASM 6418 from a reducing gear system broke after reaching only one third ofits expected useful life. It exhibited the typical features of an HCF torsion fatigue fracture. The centralquestion was the early initiation of the cracks. As can be seen from the macrosection (Fig. 24) of thecross-section, the crack formation took place over the complete circumference. The cracks are branchedand have a narrow opening. In the microscopic range a thin coating of corrosion products (Fig. 25) andthe ®nest crack openings are recognisable in some locations. However the microcracks emanating fromcorrosion pits (Fig. 26) must be considered as the most important indication of hydrogen-induced stresscorrosion cracking. The microstructure consists of ®ne martensite which has been tempered at very lowtemperatures. The hardness amounts to 490 HV 10, indicating a high tensile steel which is obviously notsuitable for the application described.

4. Preventative measures

4.1. Hydrogen embrittlement

In order to be able to produce e�ective measures, both the source of the hydrogen and theembrittlement mechanism must be known at least approximately. As important measures in theprevention of hydrogen damage, the following points can be mentioned:

. material Ð selection of suitable material;

. medium Ð not so easy to in¯uence, possibly by the addition of inhibitors;

. design Ð avoid notches, slots and sharp transitions, avoid local plastic deformation

Fig. 24. Cross-section of a shaft: multiple cracks, crack branching.


4.2. Stress corrosion cracking

Here the complete system must also be adequately assessed if damage caused by stress corrosioncracking is to be prevented. A pairing of the material medium can be tested in laboratory investigations

Fig. 25. Branched cracks, partially ®lled with corrosion products.

Fig. 26. Cracks starting from corrosion pits.


only to a certain extent. If stress corrosion cracking is forced during laboratory tests, electrochemicaland mechanic fracture measurements also have to be applied.

In general, the following points need to be checked:

. material Ð suitable choice of material for the medium in question, optimal heat treatment (e.g. withaustentite steels, aluminium alloys), prevention of residual stress (tensile);

. medium Ð determine the aggressive ions and if possible eliminate; screen using inhibitors, in somecases use cathodic or anodic protection or change the redox potential of the medium;

. mechanical stresses Ð detect and optimise (assembling stresses, residual stresses).

5. Conclusions

Hydrogen cracking and stress corrosion cracking produce delayed low grade deformation fractureseven in high tensile materials although the adjacent material range may not exhibit any embrittlementcharacteristics. Both types of damage are dependent on many simultaneous parameters and are thereforeaccompanied by apparent unpredictability. A comprehensive analysis as a starting point for preventivemeasures is of the utmost importance both for safety and for economical reasons.

References

[1] Faria L. Cost of fracture. In: Proceedings of SPT5, Vienna, 1993.

[2] Gnirss G. Hydrogen and its e�ects in welding. TUÈ 1976;17(11):367±77 [in German].

[3] Muster WJ. On hydrogen e�ects. EMPA Report No. 10848, 1982. p.2 [in German].

[4] Adda I, Philibert J. La di�usion dans les solides. Saclay, France: Institut National des Sciences et Techniques nucleÂ aires, 1966.

[5] Simon H, Thoma M. Applied surface technology for metals. Munich/Vienna: C. Hanser, 1985 [in German].

[6] Heinke G, Wagner GH. Material damage by hydrogen. Mat-Wiss und Werksto�technik 1996;27:259±66 [in German].

[7] Schmitt G, Savakis S. in: EUROCORR, 1987, p. 493.

[8] Nelson GA. Steels for hydrogen service at elevated temperatures and pressures in petroleum re®neries and petrochemical

plants. Washington DC: API, 1990 [Publ. 941].

[9] ISO 4042, Annex A: hydrogen embrittlement relief after electroplating.

[10] Stellwag B, Kaeschke H. Kinetics of H-induced stress corrosion cracking. Werksto�e und Korrosion 1982;33:274±80 [in

German].

[11] Ayeta GB, Pickering HW. J Electrochem Soc 1975;122:1018.

[12] Pickering HW, Frankenthal RP. J Electrochem Soc 1972;119:129.

[13] Johnson HH. Proceedings of the Conference on E�ect of Hydrogen on the Materials Properties and Selection in Structural

Design, Seven Springs, 1973. p. 35.

[14] Hirt JP, Johnson HH. in: NACE 32, 1, 1976.

[15] Liu HW. Trans ASME I, J Basic Eng 1970;92:6.

[16] Parkins RN. Environment sensitive fracture and its prevention. Brit Corr J 1979;14:5.

[17] E�ertz PH, Forchhammer P, Hickling J. VGB Kraftwerkstechnik 1982;62(5):390 [in German].

[18] Logan HJ. J Res Natl Bur Stand 1952;48:99.

[19] Speidel MO, Magdowski RM. Proceedings of the Second International Symposium on Environmental Degradation of

Materials in Nuclear Power Systems Ð Water Reactors, American Nuclear Society, Monterey CA, USA, 1985. p. 267.

[20] Beavers JA. Stress corrosion cracking of copper alloys. In: Jones RH, editor. Stress corrosion cracking. Ohio: ASM Int, 1992.

[21] Hickling J. In: Lange G, editor. Systematic analysis of technical failure. DGM, 1983. p. 291.

[22] Landgren W, Mattson E. Brit Corros J 1976;11:80.


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