Sensitivity of pipelines with steel API X52 to hydrogen embrittlement

Abstract

The following cases of hydrogen influence on pipeline metal were considered: gaseous hydrogen under internal pressure in notched pipes and electrochemically generated hydrogen on external pipe surface from soil aqueous environment. The burst tests of externally notched pipes under pressure of hydrogen and natural gas (methane) were carried out after the pipe has been exposed to a constant ''holding'' pressure. It has been shown that even for relatively ''soft'' test conditions (holding pressure p ¼ 20 bar and ambient temperature) the gaseous hydrogen is able to penetrate into near surface layers of metal and to change the mechanism of local fracture at notch. The sensitivity to hydrogenating of given steel in deoxygenated, near-neutral pH NS4 solution under soft cathodic polarisation was studied and the assessment local strength at notches in pipeline has been made for this conditions. Here, the relationship between hydrogen concentration and failure loading has been found. The existence of some critical hydrogen concentration, which causes the significant loss of local fracture resistance of material, was also shown.

Hydrogen damage of steels: A case study and hydrogen embrittlement model

“…This indicates the material brittleness and change in the dominant hydrogen embrittlement mechanism, which was confirmed by impact toughness testing and fractographic studies of the fractured surface in the Charpy specimens [6]. The abrupt change in mechanical properties is a function of the hydrogen content in the metal, whereby it appears in exceeding the "critical hydrogen concentration" [6,12,21,27].…”

“…When reaching a critical hydrogen concentration, different authors suggest that different phenomena occur in steel: changes in the damage mechanism from decohesion to the formation of micro crevices at the grain boundaries [29]; local cracking initiation -establishment of the local fracture criteria [30] and critical loss of the material local strength at the notch in the presence of hydrogen [27]. In this study, the term ''critical hydrogen concentration'' defines the concentration level which causes critical drop in the impact strength of the material and sharp ductile-brittle fracture transition [6,12,21] in the presence of hydrogen.…”

“…The orientation of each specimen is transverse to the axis of the tube, whereby the notches on the set of three specimens, on both sides of the fracture, are oriented towards the fracture edge. The non-standard, "Roman tile"-like geometry[27,28], Charpy V-1 notched specimens (1mm/45°) were used (dimension: 3x3x44mm and 3x6x44mm),Fig. 1b.Before testing, specimens were flattened as necessary at extremely slow strain rate.…”

Hydrogen Diffusivity in the Welding Zone of Two High Strength Experimental Microalloyed Steels

“…11,12) This is because there may be presence of H 2 S during the exploitation, processing and/or transport of hydrocarbons; thus through corrosion reactions, hydrogen ions can be produced,…”

Effect of Immersion Time on the Mechanical Properties of S135 Drill Pipe Immersed in H2S Solution

“…If overflow occurs during drilling and sulfur gases enter drilling fluid from the formation, the pH value of drilling fluid decreases rapidly. During drilling process or down time for dealing with incidents, the drilling fluid containing dissolved hydrogen sulfide contacts the steel drilling pipe, and an electrochemical reaction is formed to produce hydrogen atoms, which are diffused into steel material (Ref 4,5) and decrease the plasticity of drill pipe, namely hydrogen damage, which is one of the main reasons for drill pipe failures (Ref [6][7][8]. When drilling the formation containing H 2 S, it is necessary to take action soon to avoid performance deterioration and even hydrogen-assisted ductile failure due to long-term immersion.…”