Solubility Of Hydrogen In Steels Research Articles

An approach to coupling the gas flow dynamics and thermodynamics of hydrogen solubility in L485ME steel grade for estimation of fracture toughness

The paper presents the problem of coupling the gas flow dynamics in pipelines with the thermodynamics of hydrogen solubility in steel for the estimation of the fracture toughness. In particular, the influence of hydrogen blended natural gas transmission on hydrogen solubility and, consequently, on fracture toughness is investigated with a focus on the L485ME low-alloy steel grade. Hydraulic simulations are conducted to obtain the pressure and temperature conditions in the pipeline. The hydrogen content is calculated from Sievert’s law and, as a consequence, the fracture toughness of the base metal and heat-affected zone is estimated. Experimental data is used to define hydrogen-assisted crack size propagation in steel as well as to a plane strain fracture toughness. The simulations are conducted for a real natural gas transmission system and compared against the threshold stress intensity factor. The results showed that the computed fracture toughness for the heat-affected zone significantly decreases for all natural gas and hydrogen blends. The applied methodology allows for identification of the hydrogen-induced embrittlement susceptibility of pipelines constructed from thermomechanically rolled tubes worldwide most commonly used for gas transmission networks in the last few decades.

Effect of microstructure and inclusions on hydrogen induced cracking susceptibility and hydrogen trapping efficiency of X120 pipeline steel

The susceptibility to hydrogen induced cracking (HIC) was evaluated for X120 steels containing different amounts of Mn and Al in a H 2S environment. The hydrogen trapping efficiency was investigated by measuring the permeability ( J ∞ L) and the apparent diffusivity ( D app). The results demonstrated that larger amount of the inclusions, and larger area and volume fraction of the inclusions make steels more susceptible to HIC. The steel with a microstructure consisting of granular bainite and M/A (martensite/austenite) microconstituents is more susceptible to HIC. The ability of the microstructure and the inclusions to trap hydrogen was explained in terms of the apparent diffusivity ( D app), permeability ( J ∞ L), and solubility of hydrogen in steels ( c app). The lower the values of D app and J ∞ L and the higher the value of c app are, the more the hydrogen trapping occurs in the steel, and the more the steel is susceptible to HIC.

A model for calculating solubility of hydrogen in steel

A model has been developed for calculating the hydrogen solubility in steel on the basis of composition (S, Ti, B) and grain size, with the objective of improving the control of hydrogen content in steel products. The effects of sulphur are in agreement with previous experience, but complex effects have been observed with variations in titanium and boron contents. The model defines trap sites in crystallographic terms for the various phases and features of interest. Segregation effects have been studied using laboratory casts and with composites using continuously cast slab from which the natural segregation has been removed. Segregated regions absorb large amounts of hydrogen, but the crack threshold is reduced such that the composites have much lower safe hydrogen levels than unsegregated material. The effects of assumptions in the model on number of traps and binding energies are considered.

Role of hydrides in hydrogen entry into steel from solutions containing promoters

The saturation solubility of hydrogen in steel has been investigated by cathodically charging steel specimens in solutions of different pH values containing various promoters. Hydrogen has been determined volumetrically after vacuum extraction at 300°C. It has been established that the [H] sat vs. pH vurve for each promoter rises to a maximum [H] max and then decreases with increase in pH. This observation has led to the conclusion that the hydride of the promoter is the dominant species in the mechanism of promoter action, and support for this view is provided by the fact that [H] max increases with the bond strength (or binding energy) of the promoter hydride. Hydrogen entry into steel in the presence of promoters is facilitated by formation of a promoter hydride, which thereby weakens the Fe H bond. From the values of [H] max the order of effectiveness of the promoters studied is S > P > Se > Te > As which is contrary to the results obtained by previous workers. Nevertheless it should be emphasized that promoter action is dependent upon the pH of the solution, the precise experimental conditions of charging and the method used to evaluate hydrogen entry.

Influence of Cold-Reduction and Heat-Treatment Combinations On Hydrogen Solubility and Permeability in Steel

Abstract Tests were made to determine the effect of cold reduction on hydrogen solubility in steel. It was found that this direct relationship persisted through subsequent heat-treatment and later cold reduction. This was not true, though, of hydrogen permeability. Increasing the amount of cold reduction increased the hydrogen solubility. Increasing the amount of cold reduction also increased the hydrogen permeability until a maximum was reached (below 30 percent reduction for initially hot-rolled steel), after which the permeability decreased as the amount of cold work increased. 3.7.3

Influence of Cold‐Reduction Practice on Hydrogen Behavior in Enameling Steels

As part of a continuing study intended to relate enameling characteristics to measurable physicochemical properties, experiments were performed in which the behavior of acid‐charged hydrogen in enameling steel and the enamel‐ability of enameling steel were compared for as‐cold‐reduced and normalized lots of steel produced from hot‐rolled specimens given various degrees of cold reduction in the laboratory. Concurrent with increased cold reduction of the steel in the range 0 to about 75% was an increase in hydrogen solubility in the steel and a general decrease both in the intensity of hydrogen‐caused ground‐coat reboiling and in the tendency of the steel to develop delayed defects in direct‐white enamel coats. The influence of cold reduction on hydrogen‐caused defects in enamel coats was diminished by previous normalizing of the cold‐reduced sheet and by the heat‐treatment given the steel during the enamel‐firing process. The influence of cold reduction on hydrogen solubility in steel was only partly overcome by heat‐treatment. For as‐cold‐reduced specimens, increased cold work increased the hydrogen‐desorption rate to a maximum below 20% reduction and a further increase in reduction decreased the de‐sorption rate. For normalized specimens there was a trend for the desorption rate to decrease with an increase in the amount of previous cold reduction of the steel.

CORROSION RESEARCH ROUND‐UP

Solubility of hydrogen in steels at high temperatures and pressures. The solubility of gases in metals under these conditions, especially of hydrogen in steel, is of considerable theoretical interest not only in general metallurgy but also in connection with corrosion. The composition of several steels is tabulated and diagrams shown of apparatus set‐up, including hydrogen cylinder, gas holder, compressor, receiver, autoclave, furnace, manometers, etc. Another table gives results of three tests with each steel, showing hydrogen solubility at 500° under a pressure of 100 kg./sq.cm. There were wide differences in the steels. In the austenitic chrome‐nickel type such as 1Kh18N9T and 2Kh18N9 solubility was four times greater than with steel 20, and six times greater than with alloy steels of the ferritomartensite class. The chromium steels and steel 20 (apparently unalloyed) at 500° and under 500 kg./sq.cm. conformed to the law of solubility of gases in metals: V = K√P. Five references.—(Yu. I. Archakov and F. P. Teodorovich, Zh. prikladn. Khim., 1959 32 (12), 2667–2673.)