The corrosion performance of electroless nickel: The role of accelerated test methods compared to actual process condition evaluations in oil and gas environments

Abstract

SummaryThe corrosion resistance or protective properties afforded by coatings of nickel-phosphorus deposited from electroless nickel baths is an important reason these coatings are selected for many applications. Most industry and military specifications in effect today cite test procedures such as the 5% neutral salt spray, Acetic acid salt spray, Corrodkote or Kesternich as a measure of the corrosion performance of these coatings. These test methods, which have been used extensively in the automotive industries, are primarily designed to evaluate coating porosity and defects that allow contact of the corrosive environment with the base metal. They do not necessarily, however, quantify the corrosion performance of the coating. The acceptance of electroless nickel coatings into many industries, for applications where their long term corrosion performance in a specific process environment is a primary concern, is extremely important to their future growth. The risks associated with a premature failure of a plated part in these applications can be great for the user in terms of downtime and lost productivity. Ultimately such unforseen failures are reflected in a reluctance to consider electroless nickel coatings for new applications, impairing future market growth. This underscores the importance of adequate testing of these coatings before they are recommended for service. It also raises fundamental questions regarding the use of accelerated test procedures such as the ASTM B-117 (DIN 50021) salt spray test, compared to actual tests in process environments, as a primary basis for recommending electroless nickel coatings. This paper will explore these points in some detail.