Quantification of hydrogen diffusion and trapping in 2.25Cr-1Mo and 3Cr-1Mo-V steels with the electrochemical permeation technique and melt extractions

Abstract

The electrochemical permeation technique was used to investigate the effect of microstructure, hydrogen activity, and stationary dislocations generated by tensile straining on the permeation and degassing of hydrogen. A conventional 2.25Cr-1Mo steel, with which the existing hydrotreating reactors are made, and a 3Cr-1Mo-V steel, which is a candidate material for the future generation of reactors, were selected for this study. The effective diffusion coefficient of hydrogen derived from permeation and degassing transients shows a slower diffusivity in the V-containing steel at room temperature, regardless of the hydrogen activity. A large plastic deformation obtained by tensile straining in the homogeneous deformation domain only leads to a moderate decrease of the hydrogen diffusivity in both steels. The results are compared with the literature data on hydrogen permeation in iron and ferritic steels. On the other hand, the hydrogen content was measured with the melt extraction method after cathodic charging and subsequent aging at room temperature for different times to determine the diffusible (lattice ϩ reversibly trapped) hydrogen concentration. It was shown that the latter is larger in 3Cr-1Mo-V steel, which contains, in addition, a large fraction of "strong reversible" traps. A good concordance was found between the diffusible hydrogen concentration values computed from steady-state permeation measurements and from graphical integration of decay transients. The validity of the quantification, from permeation experiments, of the diffusible hydrogen concentration in materials with complex microstructures is discussed.

Mechanical degradation of API X65 pipeline steel by exposure to hydrogen gas

“…Necking after the peak load induces a triaxial stress state in the necked region and accelerates the brittle fracture of the specimen. Accelerated accumulation of the hydrogen-induced damage was previously reported in a triaxially stressed region [7,15,16]. The load drop is defined as the load change from the peak load to the final fracture load.…”

Numerical modeling of thermal desorption mass spectroscopy (TDS) for the study of hydrogen diffusion and trapping interactions in metals

“…4 the individual contributions of front side (x ¼ 0) and back side (x ¼ L) desorption are represented along with the total (sum of the two contributions) desorption flux. This figure shows clearly that the desorption flux for a Table 2 e Diffusion and trapping simulation parameters (1 TS) for pure iron [27,28]. Table 3 e Charging conditions for simulating Type A (homogeneous) and Type B (partial) charging.…”

“…i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 5 ) 1 e1 3 tests [28]. All simulations in this section will be carried out using these values, see Table 2 [27,28].…”

“…All simulations in this section will be carried out using these values, see Table 2 [27,28]. Two different types of hydrogen charging will be looked at: (i) Type A referring to homogeneous charging of interstitial and trapped hydrogen in the material and (ii) Type B referring to a non-homogeneous charging, imposing a concentration gradient of both interstitial and trapped hydrogen in the material.…”

“…Table 3 e Charging conditions for simulating Type A (homogeneous) and Type B (partial) charging. m Fe 0 is taken to be the solubility of H in pure Fe [28]. homogeneously charged material is made up of two simultaneous flux of equal intensity from both sample faces, due to the symmetry of the initial c H profile, whereas the second peak (T m ¼ 378 K) seen for a non-homogeneously charged material is due to the H desorption flux at x ¼ L.…”