Abstract

Armco iron and L80 steel (according to API 5CT) were charged under various conditions due to the lack of knowledge of the amount of hydrogen, which is absorbed during operation and laboratory charging. These two materials were charged in sodium chloride (NaCl), sulfuric acid (H2SO4), both with and without addition of thiourea (CH4N2S) and in H2S (NACE TM0177) at open circuit potential.

Additionally, cathodic charging was done in sodium chloride and sulfuric acid, both with thiourea added at a current density of 1 mA/cm2. The charging time was between 2 and 200 hours for both methods. Most of the immersion tests at open circuit potential resulted in hydrogen concentrations of up to 1 wt. ppm, while cathodic loading led to values of up to 4 wt. ppm. In addition, the NACE TM0177 test provided the highest hydrogen concentrations and was the only test to show higher hydrogen concentrations for the Armco iron than for the L80 steel.

Introduction

Facing the increasing industrial requirements on iron and steel products the importance of investigating hydrogen embrittlement has been rising straightly since Johnson first described the influence of hydrogen on the mechanical properties of iron and steel in 18741. Since this day a lot of effort has been done on understanding and describing the mechanism of hydrogen embrittlement and how absorbed hydrogen performs in materials.

This work aims in providing a deeper knowledge about the processes of hydrogen uptake in iron and steel in general and to determine the hydrogen uptake of L80 steel and Armco iron under various conditions. Beside the uptake also the desorption of hydrogen from L80 steel and Armco iron was investigated.

For the absorption into solid metals hydrogen is required to be in atomic form due to its diffusibility. The atomic hydrogen is adsorbed at the interface of metal and the surrounding media from where it is absorbed into the bulk material. Absorption can take place in three different ways.

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