The hydrogen permeation technique has been successfully used in assessing materials susceptibility to suffer corrosion-related damage in different environments. A methodology has been developed which entitles the use of hydrogen permeation monitoring as a non-intrusive online corrosion sensor with remarkable advantages in particular applications.
There are many oilfields in Venezuela which produce associated gas with high partial pressures of CO2 and/or H2S and were designed long time ago with carbon steel tubing and pipelines based on the lack of produced water. Although the presence of crude oil may inhibit corrosion, there is an increase concern because the water cut is increasing and there is no predictive model that accurately takes into account the crude oil effect on corrosion rate, sulfide stress cracking, or hydrogen induced cracking. In designing the most cost effective and safe solution to this problem, the use of non-intrusive hydrogen permeation sensors have been considered.
Hydrogen permeation has been used for decades in relation to corrosion assessment. The methods used in the field to monitor internal corrosion rates of pipelines or reactors, non intrusively, are based on the detection of the atomic hydrogen permeating out of the external wall by either electrochemical oxidation or pressure increase.
The electrochemical hydrogen permeation method was developed by Devanathan and Stachurski 1 for measuring hydrogen flux in the laboratory and was readily adapted for use in the field. In the laboratory, this method has been successfully utilized for studying hydrogen diffusion in metals and hydrogen evolution mechanism, as well as measuring hydrogen entrance into metals produced by corrosion, cathodic protection, galvanizing or welding.
This electrochemical technique is based on the oxidation of the atomic hydrogen exiting the metallic surface, by maintaining its electrode potential at a sufficient anodic value in a suitable electrolyte. In the field, the electrochemical method was adapted as a non-intrusive hydrogen permeation monitor, with some limitations mainly due to the need for liquid electrolytes that could leak and were generally aggressive? Recently, a new electrochemical sensor based on fuel cell technology was developed, which requires no liquid electrolytes, has longer life time, needs no external power and can be adapted for high temperature applications 2.
The other technique most commonly used in corrosion field is based on the increase of pressure caused by the recombination of the atomic hydrogen diffusing out of the metal into a hermetic chamber. This technique was mainly developed to be used in the field, and has been adapted as intrusive or non- intrusive hydrogen probes. For the non-intrusive measurement of hydrogen permeation, the hermetic chamber is previously evacuated and the vacuum loss measured 3.
The advantages and limitations of the non intrusive hydrogen probes, as well as a mathematical model developed for correlating electrochemical with vacuum loss probes have been discussed in previous communications. It is important that quantitative relationships and models be available in order to apply laboratory correlations successfully to the field.
It is recognized that sulfide stress cracking (SSC) and hydrogen induced cracking (HIC) are both particular forms of hydrogen attack. Resistance to SSC is often the principal factor affecting the choice of materials for H2S-containing environments, since the occurrence of SSC can result in a catastrophic and potentially hazardous failure. The risk of SSC and lack of realistic knowledge of the susceptibility of materials to fail in actu