New Class of "Green" Corrosion Inhibitors: Development and Application
Authors: Denney Dennis 
Published: February 2015

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 104241, "A New Class of ‘Green’ Corrosion Inhibitors: Development and Application," by H.A. Craddock, SPE, S. Caird, and H. Wilkinson, Roemex Ltd., and M. Guzmann, BASF, prepared for the 2006 SPE International Oilfield Corrosion Symposium, Aberdeen, 30 May.

Use of chemical corrosion inhibitors is common in production and processing operations. Particularly challenging is the development of new chemistries, which maintain good protection of materials under a variety of conditions while being environmentally acceptable. This paper illustrates patented work in the chemistry of Alkylpolyglucosides (APGs) and their synergistic effect with polyaspartates. This inhibitor class demonstrated good general inhibitor performance in several oilfield brines, showed good filming characteristics under conditions of shear, and provided an excellent environmental profile.

Introduction

Chemical inhibitors play an important role in the protection and mitigation strategies for retarding corrosion. Several chemistries have been successful, primarily amines, quaternary salts of amines, and imidazolines, all of which act as filming protection agents either filming on the metal surface or on a variety of scales (e.g., calcium carbonate) deposited on these surfaces. In addition to filming characteristics, corrosion inhibitors must slow the corrosion rate, usually by a combination of increasing the anodic or cathodic polarization behavior, reducing the movement or diffusion of ions to the metal surface, and increasing the electrical resistance of the metal surface.

The mixture of crude oil, condensate, and connate and other waters (brines) can result in highly aggressive and corrosive media in contact with carbon steel. To challenge this environment further, these mixtures often are under high-flow-rate conditions, creating several shear-stress conditions.

Traditionally, chemical corrosion inhibitors needed the ability to film, within fluid mixtures, at the surface between liquid and solid (i.e., surfactant like materials) and needed resistance to removal under high-flow-rate conditions. In general, these materials are excellent corrosion inhibitors under a variety of field conditions. However, they do have performance boundaries, such as high temperature, and have properties relating to marine toxicity and biodegradation that make them less acceptable for use in highly regulated offshore environments such as the North Sea and north east Atlantic.

Producing more-acceptable environmental profiles for inhibitor properties could compromise the desired technical effects (e.g., persistent materials usually are not readily biodegradable). Similarly, several chemistries are nitrogen based and possess inherent toxic properties.

Faced with this challenge, various strategies were studied to reduce environmental effects while maintaining desired surfactant properties and persistency (e.g., amino acid, aspartic acid, and polyaspartates). However, these chemistries require high dosage rates or have insufficient biodegradation to meet the required environmental regulations.

Earlier works showed that agents other than filming surfactants could provide good corrosion protection under high-flow-rate conditions. However, the chemistry did not provide complete answers to biodegradation problems. It was found that, under certain conditions, APGs can provide good filming and protective characteristics and an excellent environmental profile without losing significant persistency.