NACE 1C184-2008

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Hydrogen Permeation Measurement and Monitoring Technology

Published By	Publication Date	Number of Pages
NACE	2008-01	11

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Description

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.

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 (>100 °C [212 °F]).

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–1) is reduced to sulfide (S–2), or by improperly operated cathodic protection systems.

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.

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.

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).

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:

Quantifying the amount of atomic hydrogen formed by a corrosive environment, providing an indirect measurement of corrosion rate (all types of monitors);
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);
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
Evaluating the effects of corrosion inhibitors (all types of monitors).

Additional information