ABSTRACT

Hydrogen permeation measurement by the collection method enables rapid detection of hydrogen emanation (efflux) from most carbon steel surfaces liable to be encountered in petrochemical production. In this paper the case is advanced for correlation of efflux data with corrosion rates, by conversion of data to an inferred hydrogen activity at the corroding face, ao, a parameter that is probably the best indicator of corrosive activity, independent of wall thickness and steel quality. This is used in evaluation of field data. Initial use of the hydrogen collection method has suggested widespread passivation of corrosion in cold sour systems, such that documented wall losses may occur as a result of only occasional and intense corrosion episodes. Conversely, in hot corrosive scenarios, inhibitors and corrosive scale are less effective in preventing a long term corrosive issue. Furthermore, above about 100 °C, 300 °F it is considered that hydrogen entry into steel can occur without the presence of a hydrogen promoter such as sour gas or hydrogen fluoride. Additionally, the permeability of steel to hydrogen increases sharply with temperature. This concurs with indications of high hydrogen permeation efflux associated with naphthenic acid corrosion.

INTRODUCTION

Hydrogen permeation monitoring has long been viewed as a prospective monitoring technique for various types of corrosion, particularly corrosion due to sour gas, H2S. A reliable and effective permeation measurement method is attractive in that it is completely non-destructive, and a measured flux (flow per unit area) of hydrogen emanating from a steel surface is directly evident of cathodic activity; since; at temperatures below 100 °C hydrogen does not enter and permeate steel due to any other cause.

In recent years the hydrogen collection method, has been developed (1~ and presented 1-3 which appears to offer extremely sensitive (pl/cm2/s), rapid (60 s) and reliable (+-10%) measurement of hydrogen efflux from steel over a wide range of steel curvature (down to (1) HydrosteelTM, marketed and manufactured by Ion Science Ltd, England 2" diameter piping) and surface temperature (up to at least 350 °C 4). In this paper we will present and discuss some preliminary corrosion measurements carried out in the field with this technology. First it is necessary to consider how effiux measurements can be used to infer hydrogen activity at the corroding interface.

This content is only available via PDF.
You can access this article if you purchase or spend a download.