In-Situ Hollow Sample Setup Design for Mechanical Characterisation of Gaseous Hydrogen Embrittlement of Pipeline Steels and Welds  
[PERSON]  
1 Department of Materials Science & Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands; [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (E.R. ); [EMAIL_ADDRESS] (V.P)  
[PERSON]  
1 Department of Materials Science & Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands; [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (E.R. ); [EMAIL_ADDRESS] (V.P)  
[PERSON]  
1 Department of Materials Science & Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands; [EMAIL_ADDRESS] (T.R. ); [EMAIL_ADDRESS] (E.R. ); [EMAIL_ADDRESS] (V.P)  
[PERSON]  
2 In-Situ Hollow Sample  
electrolyte cell and applying either a constant current or potential [15; 16; 17]. A constant potential or current forces reduction of H+ ions to H atoms on the surface that can diffuse into the steel. However, when pipelines will be used to transport gaseous hydrogen, a different charging environment is created. Gaseous hydrogen molecules will dissociate into atomic form at the steel surface, and an equilibrium will be created between the partial pressure of the gaseous hydrogen in the environment and the hydrogen concentration in the subsurface layers of the steel [18; 19]. This equilibrium concentration then enables diffusion of hydrogen into the bulk of the steel. [PERSON] et al. show that these different ways of charging a steel with hydrogen can result in completely different absorbed hydrogen concentrations [12]. They measure a hydrogen concentration of 0.24 wppm for gaseous charging compared to 3.94 wppm for electrochemical charging. Electrochemical charging was furthermore shown to load a higher amount of hydrogen into so-called shallow traps [20], which have been linked to increased HE susceptibility [3; 21]. Electrochemical hydrogen charging can therefore result in unrealistic embrittlement if used to model an application in gaseous hydrogen. Several standardised test methods of evaluating HE susceptibility exist, that test in-situ at slow strain rates [22; 23; 24]. ASTM G129 [23] describes a slow strain rate (SSR) test in-situ in an environment that causes Environmentally Assisted Cracking (EAC). ASTM G142 [22] describes a slow strain rate tensile (SSRT) test in-situ in a high pressure hydrogen gas environment. These standards require testing in an environment which contains hydrogen to allow for continuous hydrogen absorption throughout the test. This inhibits the loss of hydrogen during the test to ensure a sufficient concentration even at lower strain rates. Lower strain rates have also been shown to increase HE susceptibility since they allow for more diffusion of hydrogen towards critical areas like crack tips [11; 25; 26]. Several studies that test in-situ in gaseous hydrogen use autoclaves as a containment volume for the high pressure hydrogen gas [3; 27; 28; 29]. The requirement of specialised equipment complicates these tests considerably, especially when full-scale testing is desired [30]. Testing inside a gaseous environment can be difficult, expensive and time consuming for organizations that lack such facilities. Using a hollow specimen can circumvent many of these issues by using the specimen itself as the gas containment volume. [PERSON] and [PERSON] propose the idea of a hollow type specimen [31], which has been put into practice by several other researchers. [PERSON] uses a hollow sample setup to study several different types of steel [32; 33; 34; 35]. By combining the setup with heating and cooling apparatus, he manages to characterise at a large range of temperatures. [PERSON] and [PERSON] use a hollow sample as a containment volume for high temperature hydrogenated water [36]. [PERSON] and [PERSON] characterise the HE susceptibility of a weld metal by cracking a notched cylindrical specimen, welding the two halves back together over a part of the wall thickness and subjecting it to another test [37].