Introduction

The service life and safety of an FRP water tank depend critically on the quality of its lining anti-corrosion layer. Beijing Yuanhui FRP Co., Ltd. has found in nearly a decade of field practice that over 60% of tank leakage incidents originate from lining failure—either incomplete resin curing or fiber lay-up defects such as bubbles and delamination. This article breaks down the key technical nodes of lining anti-corrosion from the perspectives of materials science and process control.

1. Resin System Selection: The Foundation of Anti-Corrosion Performance

1.1 Common Resin Types and Application Scenarios

The lining layer directly contacts the stored medium, making resin chemical resistance the deciding factor for anti-corrosion success. Bisphenol A unsaturated polyester resin (e.g., 196# resin) exhibits stable performance in ambient drinking water, with corrosion resistance over 30% higher than orthophthalic types. For industrial wastewater or acidic/alkaline media, vinyl ester resin (e.g., Derakane 411) is recommended, withstanding temperatures up to 120°C and showing excellent resistance to strong corrosives like sodium hypochlorite and dilute sulfuric acid. In a project for a Hebei chemical plant, Beijing Yuanhui used a vinyl ester resin + glass fiber surface veil combination, which operated for five consecutive years without leakage.

1.2 Curing System and Gel Time Control

The ratio of curing agent (MEKP) and accelerator (cobalt naphthenate) directly affects the crosslinking density of the lining layer. Recommended ratio: 100 parts resin, 1-2 parts MEKP, 0.5-1 part accelerator. Gel time should be controlled at 20-40 minutes at 25°C. Too short a gel time causes exothermic cracking, while too long leads to insufficient fiber wet-out. In summer, reduce accelerator dosage slightly; in winter, preheat the resin to 20-25°C.

2. Fiber Reinforcement Layer Design and Lay-up Process

2.1 Three-Layer Structure: Surface Veil + Chopped Strand Mat + Woven Roving

The standard anti-corrosion lining adopts a sandwich structure: first layer of surface veil (30-50 g/m²) forms a resin-rich layer 0.3-0.5 mm thick with over 80% resin content; second layer of chopped strand mat (300-450 g/m²) buffers stress; third layer of woven roving (400-800 g/m²) provides structural strength. In a 10-ton tank project, Beijing Yuanhui measured a Barcol hardness increase from 45 to 58 and a two-fold improvement in abrasion resistance using this structure.

2.2 Bubble and Wet-out Control During Lay-up

Bubbles are the most common lining defect. Key measures: first apply resin, then lay the mat, then roll—resin dosage controlled at 0.8-1.2 kg/m²; use a three- or four-roller impregnator for complete fiber wet-out; after each layer, use a bristle roller or deaeration roller to expel air from center to edges. Beijing Yuanhui's on-site records show that strict implementation of deaeration reduced pinhole density from 18 pinholes/m² to below 2 pinholes/m².

3. Construction Environment and Process Parameters

3.1 Temperature, Humidity, and Curing Conditions

Ambient construction temperature should be 15-30°C with relative humidity below 75%. Below 10°C, resin curing slows or stops, requiring low-temperature curing agents or heating equipment. For a winter project in Harbin, Beijing Yuanhui used infrared heating panels to maintain the mold surface at 25±2°C, ensuring the lining layer reached over 95% cure.

3.2 Post-curing and Thermal Deformation Control

Post-curing at 80°C for 4 hours after initial cure can increase crosslink density by 10-15%, significantly improving heat and corrosion resistance. The heating rate must not exceed 10°C/hour to avoid thermal stress delamination. For large tanks (>50 tons), segmented post-curing is recommended, with each segment held at target temperature for 2 hours.

4. Quality Inspection and Acceptance Standards

4.1 Barcol Hardness and Cure Degree

Barcol hardness (GYZ-934-1) is a quick on-site method for assessing cure. The lining surface hardness should be ≥50 with a full-surface variation of no more than 10%. Values below 45 indicate incomplete cure, requiring extended curing or recipe adjustment.

4.2 Spark Testing and Hydrostatic Pressure Test

Spark testing (5-10 kV/mm) detects pinholes or cracks above 0.1 mm. Acceptance criterion: no more than one defect per square meter. Hydrostatic test: fill the tank with water and hold for 24 hours; the water level drop must not exceed 0.5% of the initial level, with no visible leakage.

Conclusion

FRP water tank lining anti-corrosion is not a single process but a systematic engineering effort spanning resin selection, fiber design, construction control, and quality inspection. Beijing Yuanhui FRP Co., Ltd. has established a full-process standard—from incoming resin viscosity testing (Brookfield viscometer, 25°C±0.5°C) to finished product spark testing—reducing the lining failure probability to below 0.5%. For special media (e.g., chlorinated water, acidic wastewater), a 30-day immersion test per ASTM C581 is recommended to validate resin-medium compatibility.