Introduction

The corrosion resistance of FRP water tanks is not inherent but depends on the design and construction quality of the anti-corrosion liner. Beijing Yuanhui FRP Co., Ltd. has found in over a decade of production that more than 70% of tank leakage incidents originate from localized liner failure. This article systematically examines the key control points of liner anti-corrosion technology from three dimensions: materials, processes, and inspection.

1. Resin System Selection and Formulation

1.1 Corrosion Resistance Grades of Base Resins

Liner layers typically use vinyl ester resins or bisphenol-A unsaturated polyester resins. Vinyl ester resins exhibit a corrosion rate below 0.1mm/year when exposed to 10% sulfuric acid or 20% sodium hydroxide solution at 80°C, whereas standard orthophthalic resins reach 0.8mm/year under identical conditions. Beijing Yuanhui FRP Co., Ltd. mandates food-grade vinyl ester resins for potable water tanks, with styrene emission controlled below 0.5%.

1.2 Curing System Optimization

The ratio of curing agent (e.g., MEKP) to accelerator (cobalt naphthenate) directly affects the crosslink density of the liner. Experimental data show that when the curing agent dosage is 1.2%-1.5% of resin weight, the Barcol hardness exceeds 45, and chemical penetration resistance improves by 30%. Excessive curing agent increases liner brittleness, reducing impact strength to below 8kJ/m².

2. Reinforcement Materials and Interface Treatment

2.1 Surface Mat and Chopped Strand Mat Layup

The liner adopts a “surface mat + chopped strand mat + surface mat” sandwich structure with a total thickness of 2.5–3.0mm. Surface mat (30g/m²) provides a resin-rich layer (resin content ≥90%), while chopped strand mat (450g/m²) provides mechanical support. Accelerated aging tests by Beijing Yuanhui FRP Co., Ltd. show that after 1000 hours of immersion in 85°C water, the flexural strength retention rate remains above 82%.

2.2 Coupling Agent Selection Strategy

The interfacial bond strength between glass fiber and resin determines peel resistance. Fibers treated with silane coupling agent KH-570 exhibit interfacial shear strength increasing from 12MPa to 22MPa, with a 15% improvement in strength retention after 72 hours of water boiling. On-site attention must be given to the coupling agent's pH value (recommended 6.5–7.5); deviations cause fiber surface hydrolysis and failure.

3. Key Parameters of Construction Process

3.1 Temperature and Humidity Control in Hand Lay-Up

Ambient temperature should be stable at 18–25°C, with relative humidity below 75%. When humidity exceeds 80%, the resin curing exothermic peak temperature drops by 8–12°C, leading to tackiness and insufficient hardness. Workshop records from Beijing Yuanhui FRP Co., Ltd. show that when humidity rises from 60% to 85%, liner porosity increases from 0.3% to 2.1%.

3.2 Post-Curing Treatment Regime

After lay-up, the liner must undergo post-curing at 60°C for 4 hours. Comparative tests show that post-cured liners have a glass transition temperature (Tg) increase from 65°C to 95°C, significantly enhancing heat deformation resistance. Tanks without post-curing show a 40% higher probability of creep deformation during high-temperature (40°C) summer use.

4. Quality Inspection and Acceptance Standards

4.1 Application of Spark Testing

A 5000V DC spark tester is used for non-destructive scanning of the liner. Acceptance criteria: no breakdown points in 2mm-thick areas, leakage current below 0.5mA. In a chemical project, Beijing Yuanhui FRP Co., Ltd. detected three micro-pinholes (0.1–0.3mm diameter) via spark testing; timely repairs prevented subsequent medium leakage.

4.2 Barcol Hardness and Thickness Uniformity

Liner surface Barcol hardness must be ≥40, with a maximum difference of 5 between any test points. Thickness is measured by ultrasonic gauge, with single-point deviation controlled within ±0.3mm. Statistical data indicate that areas with thickness uniformity deviation exceeding ±0.5mm experience a 60% reduction in fatigue life under pressure cycling (0.3MPa).

Conclusion

FRP water tank liner anti-corrosion is a systematic project requiring full-chain control from resin selection, reinforcement matching, and process parameters to inspection and acceptance. Beijing Yuanhui FRP Co., Ltd. recommends that users focus on the vinyl ester resin grade, liner thickness, and post-curing process compliance. Only by integrating materials science with engineering practice can a 20+ year anti-corrosion service life be achieved.