NACE 1C184

Abstract

<strong>Foreword</strong> <br>This NACE technical committee report has been prepared to provide basic information on hydrogen permeation measurement and monitoring technology. It describes the background of hydrogen permeation measurement and monitoring technology, types of hydrogen monitors available, and some applications. <br>This report is intended for use by professionals in the oil and gas industry (including production, transportation, and refining) concerned with equipment service in which hydrogen enters metals and alloys, usually steels. Applications fall into two categories: hydrogen entry in aqueous corrosive environments containing hydrogen promoters, and hydrogen entry associated with more diverse sources of hydrogen at higher temperatures (&gt;100 &#176;C [212 &#176;F]). <br>When steel corrodes in acidic media, atomic hydrogen is typically produced as a product of the cathodic corrosion reaction. A portion of the atomic hydrogen penetrates the steel and the balance combines to form molecular hydrogen (H²) and is released as bubbles of gas. The presence of promoters such as fluoride, sulfide, arsenic, or selenic compounds sometimes causes a significant portion of the hydrogen atoms to diffuse into steel. Hydrogen uptake of metals is not limited to acidic systems below pH 7. It can also occur at higher pH values when hydrogen is produced cathodically from hydrogen-containing oxidants, such as when bisulfide (HS^&#8211;1) is reduced to sulfide (S^&#8211;2), or by improperly operated cathodic protection systems. <br>At higher temperatures, increased permeability of hydrogen in metals frequently causes appreciable hydrogen entry consequent to any reaction that liberates hydrogen at the metal surface, including the dissolution of H₂ gas itself. An increase in temperature often also releases trapped hydrogen within a metal, which then migrates to the metal surface and is released as a hydrogen flux. <br>Field applications for measurement of hydrogen flux from aqueous corrosion primarily involve sulfur compounds, especially hydrogen sulfide (H2S), which often occur in produced crude oil and gas streams. H2S may also be present in process stream condensates downstream from crude oil and gas production (e.g., in gas plants and sulfurremoval units). Additional H2S is released from the breakdown of sulfur compounds during certain refinery processes (e.g., in desulfurization processes such as hydrotreating and hydrocracking). Additionally, hydrogen flux is used to monitor hydrofluoric acid (HF) corrosion in HF alkylation units where the HF is a catalyst. <br>High-temperature field applications for hydrogen flux measurement include naphthenic acid and sulfidic corrosion, which accompany distillation of acidic and highsulfur oil feedstock. Hydrogen also enters into metals and alloys at high temperatures in hydrogen-containing atmospheres or during manufacturing or fabrication operations. Measurement of hydrogen during bake-out operations following such processes is also of interest. Applications also exist in other industries, such as the chemical industry and plating industry (e.g., hot-dip galvanizing, electrochemical, and electroless metal plating). <br>Hydrogen monitors are used for various purposes depending on the design of the monitor. Each type of monitor is suited to one or more purpose. These include: <br>(a) Quantifying the amount of atomic hydrogen formed by a corrosive environment, providing an indirect measurement of corrosion rate (all types of monitors); <br>(b) Quantifying the amount of atomic hydrogen transmitted through a pipe or vessel wall because of a corrosion reaction at the entry face, providing a direct measurement of hydrogen flux available for damage mechanisms such as hydrogen-induced cracking (HIC) (external, nonintrusive monitors); <br>(c) Quantifying the amount of hydrogen out-gassed from a metal or alloy during thermal treatments to remove hydrogen prior to operations such as welding (hydrogen collection method); and <br>(d) Evaluating the effects of corrosion inhibitors (all types of monitors). <br>This technical committee report was originally prepared in 1984 by NACE Task Group T-1C-9, a component of former Unit Committee T-1C&#8212;Corrosion Monitoring in Petroleum Production. Unit Committees T-1C and T-1D were combined, and this report was reviewed and reaffirmed in 1995 by Unit Committee T-1D&#8212;Corrosion Monitoring and Control of Corrosion Environments in Petroleum Production Operations. This report was revised in 2008 by Task Group (TG) 137&#8212;Hydrogen Permeation Measurement and Monitoring. TG 137 is administered by Specific Technology Group (STG) 62&#8212;Corrosion Monitoring and Measurement: Science and Engineering Applications and is sponsored by STG 31&#8213;Oil and Gas Production: Corrosion and Scale Inhibition and STG 34&#8212;Petroleum Refining and Gas Processing. It is issued by NACE International under the auspices of STG 62.