Hydrogen damage, monitoring, and prevention in the oil refinery

The aim of this work is to analyse hydrogen damage, monitoring, and possible prevention at the oil refineries' units. Hydrogen gas occupies an essential place in the processes in the oil refining industry: hydrodesulfurizers, hydrocrackers, and catalytic reformers. In addition to these processes, there are some sources of hydrogen gas arising from corrosion of carbon steel equipment in contact with aqueous solutions of acids, such as H₂S (sour water), HC1, HCN, H₂SO₄, and HF. High temperature chemical attack of carbon steel equipment by naphthenic and other organic acids can be related to hydrogen damages owing to appearing of hydrogen gas on metal surface as a result of such attack. Historically many names of hydrogen damages appeared: hydrogen degradation, hydrogen embrittlement, hydrogen blistering, decarburization, hydrogen stress cracking (HSC), hydrogen attack, high temperature hydrogen attack (HTHA), hydrogen-induced cracking (HIC), also known as stepwise cracking (SWC), stress-oriented hydrogen-induced cracking (SOHIC), sulfide stress cracking (SSC). This profusion of names does not always correctly elucidate and explain them, and can even confuse and complicate their detection, understanding, monitoring, and control. From analyzing the literature on this subject and based on our own experience, we differentiate all hydrogen damage failures into two main groups based on two mechanisms: electrochemical processes (mainly at low temperature, up to ~100°C) arising from acid corrosion and cathodic protection, and high temperature (between 200 and 900°C) arising from the presence of hydrogen gas at high pressures. Examples of hydrogen damage are given for the various units of oil refineries. Different monitoring methods were developed for detection of possible hydrogen damages. Hydrogen can be detected either in intrusive or non-intrusive devices called hydrogen probes. Hydrogen that penetrates through a metallic wall can be detected with manometric (hydrogen pressure,) or vacuum method, electrolytically (hydrogen ionization from H atoms into H⁺ ions), heat conduction (gas chromatography), vacuum extraction at 400°C, or hydrogen effusion. Monitoring methods are critically reviewed. Preventive measures of hydrogen failures are differentiated into two groups according to low (electrochemical) and high temperature (dissociation of hydrogen molecules) mechanisms. The first group includes protective measures from hydrogen blistering and sulfide stress cracking (SSC): metallurgical measures, change of environmental conditions (removing aggressive species such as sulfides, cyanides, and arsenic compounds, neutralization, injection of inhibitors of hydrogen penetration), use of organic, inorganic, and metallic coatings, heat treatment and proper welding. The second group includes metallurgical measures (use of steels containing chromium and molybdenum, and decrease of carbon content in steel), heat treatment, and proper welding. Analysis of preventive measures of hydrogen failures was carried out and recommendations were given. Examples of hydrogen damages are given for the isomerization and hydrodesulfurizer units of oil refinery.