Unlike traditional pipe-repair "weld patch" or "steel patch" methods, vacuum-assisted, hot-work-free composite repair bonds carbon fiber cloth directly over the affected area to seal leaks and reinforce the structure. Carbon fiber's thermal expansion coefficient is very close to that of steel, giving long service life. The technique applies to steel vessels and storage tanks, providing strength reinforcement, fatigue repair and buckling repair, including local surface defects.
Advantages Over Traditional Mechanical Repairs
- High specific strength and modulus — minimal weight addition after bonding
- Tailorable design — ply schedule customised to service load and conditions
- Conforms to complex curvature — in-situ cure on shaped surfaces; the patch bonds tightly while preserving the original profile
- Lower stress concentration — bonding increases stiffness and static strength at the damaged zone and reduces crack-tip stress intensity; no new holes drilled, so no new stress raisers
- Short cycle and low cost
- Minimal equipment — primarily a repair kit and a vacuum pump
- Hot-work free — safe and reliable
Critical Technical Elements
Adhesive Selection
The adhesive is the medium that arrests the crack. Selection must match service load and environment, requiring fatigue resistance, shear and peel strength, and resistance to fluids and hygrothermal aging. Two families exist:
- Two-component adhesives — typical for room-temperature cured composite repair
- Film adhesives — used for heat-bonded cure
Patch / Substrate Matching
The composite patch should cure at the lowest practical temperature, and its thermal expansion coefficient should match the host. Boron/epoxy is common abroad but costly and difficult to process; for general industrial repair, carbon/epoxy — long used in aerospace — is more economical and well suited to complex geometry.
Surface Preparation
Mechanically remove oxidation and contaminants that impair bonding, or chemically deposit a controlled oxide layer / chemical bonding sites. The common method is mechanical grit-blast or grinding to St3 followed by a silane coupling agent.
Vacuum-Assisted Cure
The "vacuum-assisted cure" process controls pressure, temperature and time. Because the repaired zone and surrounding body form a complex thermal conductor, a dedicated vacuum pump, matched consumables and special tooling provide continuous temperature and pressure to the bondline.