Fusion Bond Epoxy Information

Fusion bonded epoxies are thermosetting epoxy coatings designed to provide corrosion prevention on underground pipelines. These coatings are capable of operating in ranges from -100°F up to 230°F—depending on which grade is chosen, soil type, moisture content, thickness, temperature and other conditions. The values below are for a range of FBE types. Specific product information should be obtained from the manufacturer’s technical data sheet.

FBE application guide

This guide outlines the application of fusion bonded epoxy to girth welds and other pipeline appurtenances such as bends and fittings.

History
Fusion bonded epoxy (FBE) has been one of the premier coatings of choice on pipelines for many years due to its durability, corrosion protection properties and ease of application. Starting in the mid 1970s, FBE was used on the girth weld area as a field joint coating. Since that time, millions of girth welds have been coated utilizing this product. In the mid 1980s, the use of FBE was expanded to include coating induction bends, flanges, valves, tees and other fittings used in a pipeline system. This allowed owner companies to have a high quality corrosion protection coating from start to destination of their pipelines. Technological advances in the application techniques allow for a low cost, high production process for battling corrosion on the weld areas of pipelines.

Definition
Fusion bonded epoxies are a one part, heat curable, thermosetting epoxy utilized for corrosion protection. FBEs are applied to heated parts in a powder form that rapidly gels from liquid to a solid and have remarkable adhesion to the steel surface. FBEs are also are very resilient coatings that resist damage during handling. FBEs are environmentally friendly and contain no volatile organic compounds (VOCs). Societies for Protective Coatings (SSPC), NACE International (NACE), and the International Standards Organization (ISO) have developed standards for surface preparation and application of FBE and will be referenced within this document.

Surface preparation
Attaining a high quality finished product requires adequate surface preparation. Initially the surface to be coated should be inspected and pre-cleaned to SSPC SP1 standard to remove any visible grease and oil. Solvents that do not leave a residue should be utilized. Preheating may be required to bring the surface temperature up to 5°F above the dew point prior to the abrasive blasting process. Open flame or induction heating is most often utilized for preheating. Following the removal of contaminants, the area should be blast cleaned using steel grit, garnet, sand or a slag product to achieve an anchor profile of 1.5 to 4.5 mils (depending on the FBE manufacturer’s recommendation) and a near white minimum cleaning should be produced. Hand blasting or semi-automated blast rings are most often used for surface preparation on girth welds. NACE Nº 2 or equivalent near white finish should be achieved. This surface will have a 95 percent gray appearance with light streaks or shadows. When blasting the girth weld area during pipeline construction, a minimum of one-half inch of the parent coating should be brush blasted to extend the anchor profile onto the parent FBE coating. Other imperfections on the steel surface such as weld splatter, slag or slivers should be removed by filing or light abrasive grinding, taking care that a minimum of the anchor profile be removed. When using a closed cycle abrasive cleaning system, frequent small additions of blast media should be incorporated to minimize fluctuations in the anchor profile and ensure an efficient operation. Any remaining blast media left on the surface should be removed using a clean brush or clean dry air. Protection from rain and other moisture sources will be required to avoid flash rusting of the steel surface.

Following the blast cleaning process, an SSPC-VIS 1 visual comparator in conjunction with a spring micrometer and replica tape can be used to ensure the cleaning standard and anchor profile has been achieved.

Pipe Heating
The surface to be FBE coated should be heated within four hours or less of the blasting process to a temperature recommended by the manufacturer prior to the FBE application. Heating in excess of 500°F may cause foaming of the FBE product or damage to the steel itself. Induction heating is the most common form of preheating due to the uniformity and speed of the induction heating process. A small mark made by a sulfur free temperature rating crayon should be applied to the surface to be heated. When this mark turns into a liquid, the surface has reached the desired temperature and the induction heating process should be ceased. This process generally takes from one to five minutes depending on ambient temperature, pipe diameter and pipe wall thickness. Following the induction heating process the surface should be brushed again to ensure the surface is contaminate free.

FBE Application
The FBE should be applied immediately following the heating process to avoid excess pipe cool down. Pipe cooling below 450° F may not fully cure. Heating the area to be coated again will prevent this from happening. The FBE is generally applied utilizing semi-automated application ring, electrostatic guns or flocking units to a minimum thickness of 14 to 16 mils. The FBE material is applied in several passes of 2 to 5 mils and should always be completed in an expedient manner to avoid lamination. The FBE will usually be dry to the touch in less than a minute and be fully cured within three minutes or less depending on the formulation of the material. Handling and testing may commence once the applied coating cools too approximately 200°F.

Testing
After the coating process has been completed, field testing occurs. This testing most commonly includes visual inspection, thickness testing utilizing a magnetic pull off gauge and a holiday test set at 125VDC per mil. Failure of the visual inspection or thickness readings should be repaired by patch compound for small isolated areas or stripping and recoating for large areas.

Other tests that can be performed on the applied coating include a DSC analysis to prove cure, cross hatch adhesion test, cathodic disbondment to ensure the coating will deteriorate over time, hot water resistance to ensure no moisture migration through the coating, impact to determine resilience, porosity to determine foaming and bend tests to determine the presence of backside contamination. These tests are all forms of destructive testing and will result in a reduction of the coating quality or a destruction of coating and pipe to obtain the test sample. These tests are generally performed as lab tests during the coating qualification and not as field tests.

Repairs
Two methods of coating repair are generally utilized: a hot melt compound and a two part epoxy repair. After identifying the coating defect, the area is cleaned by sanding or filing to remove all loosely adhered coating and rust. Next the area is preheated using a small propane torch and a hot melt compound is then melted into and around the defective area. The area is then allowed to cool to the touch and holiday detection can be repeated. Cleaning preparation for using a two part epoxy to repair the pipe will include sanding, filing or abrasive blasting for extremely large areas. The epoxy material is then mixed according to the manufacturer’s recommended ratio and applied by brush or spatula. Curing will usually occur within 30 minutes at 75°F.

Conclusion
The information provided above is a general guide to FBE application and users should consult manufacturer’s technical data for specific application information for the type of FBE used.

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