ABSTRACT
The use of dry coating on Premium OCTG connections to replace both storage and running compounds presents numerous benefits for end-users. As well as improving running performances, it keeps the well clean by preventing the discharge of dope to the environment and into the well bore and it reduces the operational costs by the elimination of storage dope, cleaning and running dope re-application.
The solution that has been developed combines: (i) an electrodeposited zinc-based metal plating, which provides anti galling properties and protects the steel from corrosion in storage conditions; and (ii) an organic topcoat to control the friction coefficient improves the running performances. An intensive test program has been performed to assess marine atmospheric corrosion performances during storage on yard and to evaluate crevice corrosion in H2S environment with this dope-free solution. Atmospheric corrosion was evaluated after long-term exposure to natural environments and accelerated cyclic corrosion tests in a lab. Resistance to crevice corrosion was assessed through specifically designed high pressure and high temperature corrosion tests in autoclaves.
INTRODUCTION
The use of dry coating on Premium OCTG connections to replace both storage and running compounds presents numerous benefits for end-users. It preserves the environment and keeps the well clean by preventing the dope discharge into the atmosphere and into the well bore; it reduces the operational costs by eliminating the need for storage dope, cleaning and running dope re-application (rig-ready solution). It improves the running performances due to less rejects and back-outs.
The Vallourec dopefree premium OCTG connections involve a multilayer coating system that is applied in the manufacturing plant directly after threading, as an alternative to storage and running dopes that are usually applied at different stages of the product lifecycle. The coating system consists of a zinc-nickel electroplating, which provides anti-galling and long-term corrosion resistance, and a solid polymer-based topcoat whose main role is lubrication (Figure 1). The polymer topcoat can be either a soft wax-type coating or a thermoset paint.
