Introduction

FRP water tanks are widely used in municipal water supply, industrial storage, and fire reserve. The lining system is the most critical layer determining tank longevity and water quality. Based on field data from Beijing Yuanhui FRP Co., Ltd., this article outlines the technical framework for lining anti-corrosion design, from material selection to acceptance testing.

1. Resin System Selection

1.1 Food-Grade Compliance for Potable Water

For drinking water tanks, the lining must use resin certified to GB/T 17219 standards. Vinyl ester resins, such as Dow DERAKANE 411-350, retain 92% Barcol hardness after 30 days in 60°C water, compared to a 35% loss for orthophthalic polyester resins. Beijing Yuanhui FRP Co., Ltd. specifies vinyl ester as the default for all potable water projects.

1.2 Chemical Resistance for Industrial Media

When storing 15% hydrochloric acid, bisphenol-A epoxy linings exhibit a corrosion rate below 0.05 mm/year. For sodium hypochlorite, HET acid resin is recommended. In a chemical plant case in Hebei, Beijing Yuanhui used phenolic epoxy lining for fluorine-containing wastewater; after 3 years, thickness loss was only 0.2 mm.

2. Fiber Reinforcement Architecture

2.1 Resin-Rich Surface Layer

The lining consists of C-glass surface veil (0.3 mm thick), chopped strand mat, and helical winding. Resin content must be 65-75%. C-glass veils with 5 µm fiber diameter reduce capillary penetration by 40% compared to E-glass veils. Beijing Yuanhui's laboratory tests show water absorption of 0.12% after 1,000 hours in 10% sulfuric acid, well below the 0.5% industry limit.

2.2 Structural Layer Mechanics

The structural layer uses E-glass direct roving wound at a 54.75° helical angle. For tanks over 3 meters in diameter, additional hoop windings are added to achieve a bending strength above 150 MPa. Beijing Yuanhui employs computer-controlled winding machines to maintain lining thickness within ±0.2 mm tolerance.

3. Construction Process Controls

3.1 Mold Surface Preparation

Mold roughness must be Ra ≤ 0.8 μm. After sealing, PVA release agent is sprayed to 8-12 μm thickness. Beijing Yuanhui's shop standard requires finished lining surface roughness Ra ≤ 1.6 μm, significantly reducing scale adhesion.

3.2 Cure and Post-Cure Schedule

Lining is cured at 25±2°C for 24 hours, followed by 4 hours at 60°C post-cure. Infrared thermography checks for temperature uniformity; any area with a >5°C deviation is reworked. A southern project experienced lining peel strength dropping from 8 N/mm to 3.5 N/mm due to insufficient winter curing, later resolved by hot-air circulation.

4. Inspection and Defect Remediation

4.1 Barcol Hardness and Spark Testing

Acceptance requires surface Barcol hardness ≥ 40. Spark testing at 15 kV scans the entire lining; no discharge points are acceptable. Beijing Yuanhui's records show a 92% first-pass rate across 1,000 tanks. Common defects include micro-bubbles (<0.5 mm) and local resin starvation, repairable by resin brushing.

4.2 Leak Test and Water Quality

The tank must hold water for 72 hours with a water level drop ≤ 5 mm. Water samples are tested for color ≤ 15, turbidity ≤ 1 NTU, and residual chlorine consumption ≤ 0.5 mg/L. In a Tianjin project, standard curing agents caused styrene monomer leaching; switching to low-styrene resin brought all parameters into compliance.

Conclusion

FRP water tank lining anti-corrosion requires systematic engineering—from resin selection and fiber architecture to process control and inspection. Beijing Yuanhui FRP Co., Ltd. has reduced lining failure probability to below 0.5% through material databases, cure curve models, and traceable QA records. It is recommended that procurement specifications clearly define lining thickness, resin type, and test standards, with third-party witnessing rights reserved.