Embrittlement hydrogen

Hydrogen embritdement affects not only ferrous alloys. It is also important in many other alloys of great engineering importance, in particular titanium- and 

Hydrogen reaction embrittlement is a phenomenon in which the hydrogen chemically reacts widi a constituent of the metal to form a new microstructural element or phase such as a hydride or gas bubbles ( blistering ), e.g., methane gas if combined with carbon, or steam if combined widi oxygen. These reactions usually occur at higher temperatures. They result in the formation of blisters or expansions from which cracks may start to weaken the metal. 

Environmental hydrogen embrittlement means that the material was subjected to a hydrogen atmosphere, e.g., storage tanks. Absorbed and/or adsorbed hydrogen modifies the mechanical response of the material without necessarily forming a second phase. The effect occurs when the amount of hydrogen that is present, is more than the amount that is dissolved in the metal. The effect strongly depends on the stress imposed on the metal. It also maximizes at around room temperature. 

To which extent metal is degraded by hydrogen is influenced by strain (tension, frequency, stretch velocity), specimen geometry (notches, bad welds, geometric inhomogeneities), the medium (pressure variation, temperature, impurities), and material (chemical composition, fabrication, heat treatment, welding joints) [67]. 

Several mechanisms have been proposed which might explain at least partially the degradation of metal by hydrogen embrittlement and which might act simultaneously  

Molecular hydrogen precipitation forming high pressures and compound formation are other mechanisms identified. 

The manifestation of hydrogen embrittlement in structural metals is enhanced susceptibility to fracture. Hydrogen reduces typical measures of fracture resistance such as tensile strength, ductility, and fracture toughness, accelerates fatigue crack propagation, and introduces additional material failure modes 

7 Hydrogen permeability for several alloys as a function of temperature the solid lines represent the range of temperature over which the measurements were made, and the dotted lines are extrapolations of exponential form to room temperature (298 K). The austenitic Fe is an average relationship for a number of austenitic stainless steels [18] the low-alloy Fe alloy is quench and tempered 4130 [191 the non-ferrous alloys are all pure metals Ni [20] Al [21] Cu and Au [22]. Measurements made in hydrogen isotopes were corrected to hydrogen using classical rate theory [17]. 

2 Effect of yield strength on the threshold stress intensity factor (Kjh) for crack propagation in hydrogen gas (a) low-alloy steels [5] and (b) austenitic steels [17]. 

3 Fracture toughness (J-integral) results for a solid-state inertia weld (IW) and gas-tungsten arc (GTA) fusion weld in the austenitic stainless steel 21Cr-6Ni-9Mn (adapted from Somerday ef al. [28]). Results are shown for the hydrogen-exposed and non-exposed conditions. Data for the base metal are included for comparison. 

Structural metals become more susceptible to hydrogen embrittlement as the materials are exposed to higher gas pressures. Thermodynamic equilibrium between hydrogen gas and dissolved atomic hydrogen is expressed by the general form of Sievert s Law, i.e. C = Sf [16]. This relationship shows that as fugacity (pressure) increases, the quantity of atomic hydrogen dissolved in the material increases consequently, embrittlement becomes more severe. 

Hydrogen can dissolve in metals and modify their properties. This phenomenon is a frequent cause of damage, as it does not require that the metal be directly exposed to gaseous hydrogen most often the hydrogen forms at the metal surface itself by an electrochemical reaction. Three sources of hydrogen can be identified that lead to embrittlement of metals  

Certain processes in the chemical and petroleum industries use gaseous hydrogen at high-pressure. Under these conditions, some hydrogen may dissolve into the walls of autoclaves and piping systems made of metal and damage them. 

Corrosion reactions taking place in acidic environments give off hydrogen. Similarly, chemical surface treatments such as pickling of steel, or phosphatizing under acidic conditions produce hydrogen at the metal surface. 

When dissolving into a metal, hydrogen molecules dissociate into atoms  

In this equilibrium, H2 represents gaseous molecular hydrogen, and H, designates the atomic hydrogen dissolved in the metal. The equilibrium constant is written as  

Compatibility of Titanium, Zirconium, and Tantalum with Selected Corrodents 

The chemicals listed are in the pure state or in a saturated solution unless otherwise indicated. Compatibility is shown to the maximum allowable temperature for which data are available. Incompatibility is shown by an X. A blank space indicates that data are unavailable. When compatible, corrosion rate is 20 mpy. 

Source From P.A. Schweitzer. 2004. Corrosion Resistance Tables, Vols. 1-4, 5th ed.. New York Marcel Dekker. 

Gaseous hydrogen has had no embrittlement effects on titanium. The presence of as little as 2% moisture effectively prevents the absorption of molecular hydrogen up to a temperature as high as 600°F (315°C). This may reduce the ability of the titanium to resist erosion, resulting in a higher corrosion rate. 

The crevice corrosion resistance can be improved by alloying titanium with elements such as nickel, molybdenum, or palladium. Consequently, grade 12 and the titanium-palladium alloys are more resistant to crevice corrosion than unalloyed titanium. 

---

Gibala R and Hehemann R F (eds) 1984 Hydrogen Embrittlement and Stress Corrosion Craoking (Metals Park, OH American Soceity of Metals)... 

Many elemental additions to copper for strengthening and other properties also deoxidize the alloy. A side benefit of such additions is elimination of susceptibihty to hydrogen embrittlement. Such deoxidizing additions include beryllium, aluminum, siUcon, chromium, zirconium, and magnesium. 

CllO. The most common commercial purity copper is CllO. The principal difference between CllO and C102 is oxygen content which typically can be up to 0.05% in CllO. Oxygen is present as cuprous oxide particles, which do not significantly affect strength and ductiHty, but CllO is susceptible to hydrogen embrittlement. The properties of CllO are adequate for most appHcations and this alloy is less cosdy than higher purity copper. 

S tandard Methods of Test for Hydrogen Embrittlement of Copper, ASTM B 577, American Society for Testing and Materials, Philadelphia, Pa., 1992. Welding Braying and Soldering Vol. 6, Metals Handbook, 9th ed., ASM International, Materials Park, Ohio, 1983. 

Cathodic treatment of steel parts in acids could be expected to contribute significantly to hydrogen embrittlement of the part if the steel has been previously heat treated to over 40 HRC. Cold-worked steel is susceptible at a lower hardness. Some work shows more embrittlement from the plating bath than from preplate treatments (36). 

Analysis methods for hydrogen absorbed in the deposit have been described (65), and instmments are commercially available to detect hydrogen in metals. Several working tests have been devised that put plated specimens under strain and measure the time to failure. A method for cadmium-plated work has been described (66) as has a mechanical test method for evaluating treatments on AlSl 4340 Steel (67). Additional information on testing for hydrogen embrittlement is also available (68). 

A.STME326, Std. Test Methodfor Electronic Hydrogen Embrittlement Testfor Cadmium ElectroplatingProcesses, American Society for Testing and Materials, Philadelphia, Pa. 

Certain anaerobic bacteria capable of producing hydrogen may, under special circumstances, contribute to hydrogen embrittlement of some alloys. Once again, if such mechanisms operate, they have very limited applicability in most cooling water systems. 

Cathodic protection can stifle SCC in some metal systems. However, if cracking is the result of hydrogen embrittlement rather than SCC, the use of cathodic protection can intensify cracking. 

An interesting field of application is the protection of tantalum against hydrogen embrittlement by electrical connection to platinum metals. The reduction in hydrogen overvoltage and the shift of the free corrosion potential to more positive values apparently leads to a reduced coverage by adsorbed hydrogen and thereby lower absorption [43] (see Sections 2.1 and 2.3.4). 

At elevated temperature and pressure hydrogen embrittlement can result Most metals when gas is moist. Galvanized pipe or brass or bronze fittings... 

Hydrogen embrittlement is due to the reaction of diffused hydrogen with a metal. Different metals undergo specific reactions, but the result is the same. Reaction with hydrogen produces a metal that is lower in strength and more brittle. 

Hi.S may cause hydrogen embrittlement in certain metals. Figures 7-1 and 7 -2 show the H2S concentration at which the National Association of Corrosion Engineers (NACE) recommends special metallurgy to guard against H9S corrosion. 

Basically, tliere are two classes of anunonia converters, tubular and multiple bed. The tubular bed reactor is limited in capacity to a maximum of about 500 tons/day. In most reactor designs, the cold inlet synthesis gas flows tlirough an annular space between the converter shell and tlie catalyst cartridge. This maintains the shell at a low temperature, minimizing the possibility of hydrogen embrittlement, which can occur at normal synthesis pressures. The inlet gas is then preheated to syntliesis temperature by the exit gas in an internal heat e.xchaiiger, after which it enters tlie interior of the anunonia converter, which contains tlie promoted iron catalyst. 

---