The Benefits of Using Internal Plastic Coatings on Chrome Tubulars
Authors: Lauer Robert S. 
Published: October 2008

Chromium alloy tubulars are fast becoming the material of choice for environments where CO2 corosion is of concern. Prior to this point, internal plastic coatings had been one of the main ways of controlling corrosion on carbon steel for similar type applications. As the concern about corrosion has minimized with the chrome tubing, internal plastic coatings are being used in new and innovative ways to increase the efficiency of the overall well dynamics, as well as protect the tubing from flow assurance concerns as well as ancillary corrosion concerns as the well matures. The use of internally coated chrome tubing for improved hydraulic efficiency is gaining momentum in the industry. This use of internal plastic coating has proven tremendous economic advantages in improved flow, decreased utility consumption or decreased construction costs. In addition to this, internal coatings have proven a positive effectiveness with respect to the deposition mitigation aspects of flow assurance in conjunction with or as a stand-alone treatment. A completely un-expected benefit has been the protection of the chrome tubing from other forms of corrosion. This value was determined not by theory or laboratory data, but by actual statistical analysis of the inspection reports from the used material. As the costs to drill, complete, and produce a well increase, and as the industry moves into deeper water, it is imperative to have either multiple systems to ensure protection or to have systems that will perform multiple functions. Protecting and maximizing the usage of these assets is becoming key.

Introduction

Corrosion and effective corrosion control can mean the difference between a successful operation and an expensive oil and or gas well. The cost of different types of corrosion mitigation treatments in conjunction with the costs of shutting in a well, working it over to pull the tubing, or fishing the tubing can be huge. It is these costs as well as real and perceived problems with existing methods of treatment (chemical inhibition, composite materials, organic and inorganic coatings) that has lead the industry into finding alternative methods of protection. The use of corrosion resistant alloys (CRA) is becoming an industry standard, where economically feasible, for handling potential corrosion concerns as well has offering increased erosional velocity capability. Most of the CRA's are manufactured by alloying differing levels of elements; such as chromium, molybdenum, or nickel with iron. The expense of these alloys has led to the practice of trying to use some of the lower concentration alloys for this protection.

The chromium alloys have become the product of choice for dealing with CO2 corrosion. The most prevalent of these alloys used today is 13% chrome, while higher concentrations from 15 to 25% chrome can be used in more severe environments. Corrosion from CO2, while of major concern, is not the only species that can be corrosive in these environments. Corrosion from elevated levels of oxygen and chlorides, as well as excessive exposure to certain acids can be detrimental to these chromium alloys.