Metrological Assurance of Measurement of Hydrogen Concentration in Metals – a Basis for Safety in the Oil and Gas Industry

Abstract

It is demonstrated that metal properties depend strongly on both hydrogen concentration, and on its redistribution with respect to bonding energy. According to accident statistics presence of hydrogen within metal is in many cases the main reason for metal structure breakdown with occurrence of internal stresses. It is concluded that the lack of a single metrological hydrogen concentration measurement system makes it impossible to introduce extensively an effective and reliable method for production monitoring and accident prevention. Hydrogen is contained in all metals and alloys. In contrast to the majority of other alloy components, it has a very strong effect on material mechanical properties. The degree of the effect of small hydrogen concentrations on metal proper- ties may only be compared with phosphorus. The lack of necessary monitoring of hydrogen content in a metal promotes the task of measuring its concentration to a paramount category. According to statistics, in the last 30 years the reason for 62.7% of all bulk oil tanker accidents in our country was brittle failure, connected with hydrogen accumulation, and only 12.4% of accidents occurred as a result of ignition or explosions. The practice of studying operating vessels shows that their metal walls are often subject to deep pitting corrosion, as a consequence of which there is rapid local breakdown. At the boundary of an internal welded joint and wall surface, there is intergranular corrosion. Metal corrosion leads to hydrogen embrittlement for steel from which a vessel is manufactured. Hydrogen brittleness and wall delamination is one of the main reasons for the accident rate in main oil and gas pipelines. Due to a significant hydrogen concentration in raw oil and gas at sites it is necessary to prepare pipelines from special expensive grades of steel, but this only increases service life, and the problem of hydrogen brittleness is retained. The effect of hydrogen on metal properties has been studied for more than 150 years. Cases of hydrogen brittleness have been studied a great deal, and there are experimental data about a threshold hydrogen concentration with which it arises. As a rule, this is a very low concentration in the range 0.4-50 ppm. In addition, quantitative data do not fix a common standard and traceability of existing standards to a primary standard, and this leads to marked scatter of results with measurements in dif- ferent laboratories. Divergences comprise a factor from 0.2 to 2, and in the case of nanomaterials it reaches a factor of 500 (1). Contemporary measuring equipment, available on the market, differs considerably both with respect to the method for hydrogen extraction from a sample, and the recording principle. Measurements of hydrogen concentration in identical