Field joint coating involves the process of protecting welded line pipe joints for onshore and offshore applications in situ by applying a Fusion Bonded Epoxy, liquid epoxy Heat Shrink Sleeves. These coatings are crucial as they provide long-term corrosion protection and thermal insulation performance. They offer excellent adhesion to the substrate that is to be protected and exceptional compatibility with the factory or mainline coating system. However, field joint coatings are considered the weakest point within a pipeline primarily due to compatibility issues between factory applied or mainline coating and the selected material used to protect the field joint.
Fusion Bonded Epoxy
The same grade of FBE powder or other approved equivalent is applied to the line pipe, custom coating pieces and field joints, providing continuous corrosion protection along the entire length of the pipeline. The epoxy coating is applied in powder form by hand spraying onto a blast cleaned and pre-heated weld area. Once in contact with the hot pipe, the powder melts, flows and cures, forming a coating with excellent adhesion and resistance to cathodic disbandment.
Application Process:
- After applicable surface preparation, the field joint area shall be uniformly preheated, using an induction heating coil to a temperature as recommended by the manufacturer.
- The FBE shall be immediately applied once the joint area attains the temperature, with a minimum overlap of 25 mm onto the plant applied existing coating.
- The coating shall be cured.
Heat Shrink Sleeves
Supply and installation of external polyethylene heat shrink sleeve for pipes, bends, fittings and girth weld joints. Heat shrink sleeves have thick radiation cross-linked polyolefin backing that is coated with specially formulated high temperature sealant. During installation, the sealant melts and flows, filling all surface irregularities and bonding to the substrate protecting the joint from mechanical damage and corrosion.
Application Process:
- After welding, the weld area shall be cleaned with the approved cleaning method.
- The weld area is then preheated as per the operators’ recommendations.
- The sleeve is positioned to provide the correct overlap on the plant coating when shrinking is completed.
- Heat the sleeve to the specified surface temperature with a gas torch or other heat source.
Liquid Epoxy
Liquid epoxy is easier to apply than powder FBE epoxy, especially in field conditions. The liquid form allows for easier mixing and application, making it more convenient and efficient for use onsite. Liquid epoxy has a faster cure time than powder FBE epoxy, this means that the coating can be applied quickly reducing the overall downtime for the pipeline. It also has better adhesion properties than powder FBE epoxy, particularly in wet or humid conditions. This makes it more effective in protecting the pipeline against corrosion and other forms of damage.
