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PublisherNACE InternationalLanguageEnglish
Document ID 08029
Content TypeConference Paper
TitleCORROSION TESTING OF FLUOROCOATINGS FOR OIL/GAS PRODUCTION TUBING
AuthorsRichard Albert and Laurence W. McKeen, DuPont Fluoroproducts; Jurgen Hofmans, DuPont Belgium
SourceCORROSION 2008, March 16 - 20, 2008 , New Orleans LA
Copyright2008. NACE International
Keywordssour gas, corrosion, coatings, production tubing, fluoropolymers
PreviewABSTRACT

Fluoropolymers are well known for their non-stick properties. They also possess outstanding chemical resistance even at high temperatures. Coatings made from fluoropolymers also possess these properties. The oil and gas industry has believed that fluoropolymer coatings do not work in production tubing because they do not adhere sufficiently. In this paper, we report on a series of new fluoropolymer coatings which have been designed to provide excellent adhesion, even under harsh conditions. A testing protocol has been developed to compare coating performance in high temperature, high pressure, in sweet, sour or hydrochloric acid environments. This protocol and results are reviewed. It is shown that twenty four hour autoclave testing with rapid decompression can differentiate coating formulations. It is also shown that fluoropolymer based coatings offer promise for use in severe downhole environments. Additional long term or downhole testing is still required.

INTRODUCTION

Production crude oil and gas tubing is often subjected to severely corrosion environments. The carbon steel most production tubing is made from may require periodic replacement. Often, corrosion resistant alloys (CRAs) are used in place of carbon steel to increase the service life of the tubing string. CRAs are significantly more expensive that carbon steel. One approach to extend the lifetime of carbon steel tubing is to apply aprotective coating to protect the surface from the corrosive environments. Coatings based on epoxy and phenolic resins have been used for corrosion protection for many years in both production tubing and drill pipe. However, where the production fluids and gases contain higher amounts of hydrogen sulfide (H2S), these coatings may not provide adequate protection against corrosion. More corrosion resistant coating systems are needed. Fluoropolymers are resistant to a broad range of chemicals even at high temperature1. This includes corrosive materials often contained in production streams including H2S, carbon dioxide (CO2), produced salt water, hydrochloric acid, and elemental sulfur. When fluoropolymers are used to make coatings, those coatings are often called fluorocoatings. Fluorocoatings have been tried on production tubing in the past. Until recently it was generally believed that fluorocoatings do not work. They are also often called "Teflon®", but Teflon® is a DuPont trademark. Most coatings tested in the past were not DuPont Teflon® products or they were improperly selected. DuPont has hundreds of different fluorocoatings and new ones can be formulated and optimized for specific conditions and performance needs.

Properties of fluoropolymer lined or fluorocoated tubing include:

  1. Low coefficient of friction

  2. Very low free surface energy (Yc<= 18 dyne/cm).2

  3. Smooth surface leading to reduced friction factor and hydraulic improvements

  4. Flexibility (fluoropolymers typically have elongation to break of 25-300%). The high flexibility significantly reduces concerns about cracking of the coating as the pipe is handled during shipping, storage and installation and due to stresses caused by thermal expansion and contraction.

  5. Resistance to chemical attack


These properties are maintained at high operating pressure and high temperatures (up to 260 °C).

FORMULATION OF COATING SYSTEMS

All the coating systems discussed in this paper include three distinct layers differing in composition. Multiple coating layers have several advantages.
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