Performance Characteristics of Oilfield Proven Elastomers in Low-Temperature Seal Applications
Authors: Taylor K.W. 
Published: October 2008

The purpose of this paper is to present a study of the low temperature sealing capabilities of oilfield proven elastomers. In this study, application and lab tests were conducted on six types of oilfield elastomer compounds. The lab tests were conducted using conventional lab tests, as well as Dynamic Mechanical Analysis Techniques, while the application tests were conducted using conventional size -214 O-rings in nitrogen gas test fixtures. The test results of all tests were analyzed and compared for similarities.

INTRODUCTION

To avoid confusion by the use of the word "rubber" for a variety of natural and synthetic products, the term "elastomers" has come into use, particularly in scientific and technical literature, as a name for both natural and synthetic materials which are elastic or resilient, and in general, resemble natural rubber in feeling and appearance.

Elastomers are increasingly used as high integrity engineering materials; but compared to their potential, this usage is small. Major factors restricting their growth are the low level appreciation of their unique engineering properties and the difficulty in accessing suitable data for design procedures.

Elastomers used as pressure containing seals apply a pressure against their respective housings when energized, which causes compressive deformation of the seal. This compressive deformation or sealing force is time and temperature dependent, and will gradually decrease due to physical and/or chemical changes. The ability of the sealing force to remain constant is dependent upon the stress relaxation of the elastomer compound. Should stress relaxation occur, the compressive deformation or sealing force could eventually drop below the system pressure, thus casing leakage past the seal. The compressive deformation or sealing force at low temperatures depends on the ability of the elastomer to recover at that temperature. As the temperature decreases, the recovery from an applied deformation for some elastomer compounds is significantly slower. The elastomer could become progressively stiffer and leathery, lose its elastic recovery capability and become hard and brittle.

The elastic response of elastomers at high and low temperatures has been the subject of a great deal of interest and some study by many chemists because of its great technological importance, as well as its intrinsic scientific interest. Today, with more and more quality and safety minded customers, along with technological advances, the interest has intensified; thus causing the industry standards to address the nonmetallic, as well as the metallic, components.

The current sixteenth edition of the American Petroleum Institute (API) Specification 6A is published as an aid to the procurement of standardized equipment and materials, as well as instructions to manufacturers of equipment or materials covered by an API Specification.

End users that buy equipment to this specification require their suppliers to certify their equipment for temperature ratings as classified in the specification. Temperature ratings as published in Table 302.2 of API 6A (16th Edition) are:Table (Available in full paper)

Included in API 6A (16th Edition) is a section called Appendix F, Performance Verification Procedures.