Coating Application and Application Equipment
Application methods
FBE is applied by electrostatic spray or fluidized bed to a heated, blasted pipe, then cured and usually water-quenched. Three-layer systems apply an FBE primer, a copolymer adhesive, and an extruded PE or PP topcoat. Liquid coatings are applied by airless or plural-component spray; heat-shrink sleeves are common at field joints.
Critical variables
Steel substrate temperature drives FBE cure and gel time; air temperature is not a substitute. Film thickness, mixing ratio, induction time, pot life, and recoat window all affect quality. Over-thick FBE can crack or reduce flexibility; under-thickness creates holidays. Contamination between coats causes disbondment.
Equipment
Blast pots, nozzles, dew-point meters, magnetic and ultrasonic DFT gauges, holiday detectors, and plural-component proportioning equipment must be calibrated and maintained. Mixing-ratio errors are a common cause of soft, undercured films.
Traps
Using ambient temperature instead of steel temperature; exceeding the recoat window without abrading; assuming higher DFT is always better; and trusting equipment gauges without calibration.
Rule of thumb
Measure steel temperature and dew point at the pipe, verify mixing ratio by volume rather than guesswork, and check DFT on a representative pattern.
Worked example
A 4:1 epoxy is mixed 3:1 “to stretch it.” The film may feel hard but remain undercured and fail adhesion or cathodic disbondment testing; reject and recoat.