Abstract

Eleven fluid samples, taken in two groups from pipeline pigging operations in the Texas Gulf Coast region were used in this study. All of the samples contained high amounts of Iron Sulfide (FeS), Sulfate Reducing Bacteria (SRB), and Acid Producing Bactera (APB) and were producing varying amounts of hydrogen sulfide (H2S). These pipelines had historically been treated with increasing amounts of glutaraldehyde and glut/quat blends, to no avail. Increasing problems associated with microbiological activity (biofilm, corrosion, FeS, H2S) required a revised treatment regime.

The first part of this study was undertaken in order to determine a successful biocidal treatment program that would address both the planktonic and, if necessary, the sessile bacterial populations in the pipelines. Due to the perceived induced resistance to glutaraldehyde and the dirty water conditions in the pipelines, alternative dosing regimens and additional biocides were considered including tetrakis (hydroxymethyl) phosphonium sulfate (THPS), tributyl tetradecyl phosphonium chloride (TTPC), aldehydes, and cocodiamines.

The second part of the study sought to determine how to link these findings to the general and localized corrosion caused by biological activity. A corrosion inhibitor package was developed that was compatible with the customer's formulations and the recommended biocidal treatment program.

Finally, the third part of this study combined these treatments and evaluated their biocidal and corrosion inhibition efficacies on carbon steel coupons in the presence of fluids and solids.

A biocidal treatment and corrosion inhibition program are inherently intertwined and a successful treatment program must combine elements of both fields of study.

Introduction

An operating company was concerned that its biocide and corrosion mitigation strategy was not sufficient to control corrosion in their pigging operations across the Gulf Coast of Texas. They provided water samples from several pigging access points that were heavily contaminated with SRBs, APBs, black deposits and oil. H2S was present in most of the samples suggesting a heavy presence of SRBs. They suspected that the black deposits were most likely FeS caused by the presence of microorganisms interacting with their pipelines. Indeed, culture vial tests (sometimes referred to as "bug bottles") proved that the samples were heavily contaminated with microorganisms.

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