Introduction

FRP water tanks are widely used for potable water storage, industrial water treatment, and fire protection systems. However, the anticorrosion performance of the inner lining directly determines the tank's service life and water quality safety. Traditional epoxy coatings often blister or delaminate under high-temperature or acidic/alkaline conditions, leading to substrate corrosion. Based on over a decade of field data from Beijing Yuanhui FRP Co., Ltd., more than 70% of tank repair cases originate from lining failure. This article systematically dissects the material selection logic and process control points of lining anticorrosion technology from a materials science perspective.

1. Failure Mechanisms and Material Selection

1.1 Common Failure Modes

FRP tank lining failures typically include:
• Penetration failure: Water molecules infiltrate the fiber layer through micropores, causing debonding at the resin-fiber interface.
• Chemical attack: Chloride ions or acidic media accelerate resin hydrolysis; degradation rates increase 3–5 times when water temperature exceeds 40°C.
• Thermal stress cracking: Summer exposure can raise tank surface temperature above 60°C; differential thermal expansion between lining and substrate induces cracks.

1.2 Resin System Selection

Per the standard JC/T 658.1-2007 for FRP water tanks, potable water tank linings must use food-grade unsaturated polyester or vinyl ester resins. Test data show:
• Orthophthalic resin: Low cost but poor alkali resistance (service life <2 years at pH>9).
• Isophthalic resin: 30% improved water resistance, suitable for general domestic tanks.
• Vinyl ester resin: Excellent chemical resistance; after 90 days in 10% sulfuric acid, Barcol hardness retention ≥85%. In a chemical plant project by Beijing Yuanhui, vinyl ester lining maintained a surface without corrosion pits and adhesion >8 MPa after 5 years of continuous operation.

2. Lining Structure Design and Fiber Reinforcement Optimization

2.1 Anti-Permeation Layer Design

The lining typically consists of three layers:
• Surface veil (30–50 g/m²): Forms a resin-rich layer 0.3–0.5 mm thick, resin content >90%, direct contact with media.
• Chopped strand mat reinforcement (450 g/m²): Provides impact resistance; number of layers calculated based on hydrostatic pressure.
• Structural layer: Uses continuous filament winding or hand lay-up to bear tank stress. Beijing Yuanhui optimized fiber orientation at ±55° winding, achieving a hoop tensile strength of 320 MPa, 18% higher than traditional methods.

2.2 Interface Treatment and Bonding

Bond strength between lining and tank wall directly affects anticorrosion efficacy. Tests show that when surface roughness Ra ≥12.5 μm, peel strength can exceed 15 N/mm. During construction, sandblasting to Sa2.5 grade and applying a silane-coupling-agent-based primer reduces interface porosity to below 0.5%.

3. Key Construction Process Controls

3.1 Environmental Conditions and Cure Control

Resin curing is significantly affected by temperature and humidity. Beijing Yuanhui's construction specification requires ambient temperature 15–30°C and relative humidity <75%. In a winter construction case, infrared heating auxiliary cure controlled the exothermic peak temperature to 80–90°C, avoiding resin degradation (weight loss <2%).

3.2 Interlayer Interval and Bubble Elimination

After each fiber layer is placed, a de-airing roller must compact the laminate to ensure bubble diameter <2 mm and density <3 bubbles/m². The interlayer interval should be controlled within 30–60 minutes before resin gelation to avoid dry-layer defects. In a fire tank repair project, failure to control interval resulted in interlayer peel strength of only 4.2 MPa; after rework, it increased to 9.8 MPa.

4. Quality Inspection and Long-Term Performance Evaluation

4.1 Online Inspection Methods

• Barcol hardness test: Surface hardness ≥40 Barcol (ASTM D2583).
• Spark testing: Voltage set at 2 kV/mm thickness; no breakdown points allowed.
• Pull-off adhesion test: Minimum value ≥7 MPa (ISO 4624).

4.2 Accelerated Aging and Life Prediction

Using 85°C hot water immersion accelerated test (ASTM C581), Beijing Yuanhui's team applied the Arrhenius model to estimate that vinyl ester resin-lined tanks under 40°C potable water conditions have a design life of 15–20 years. In a municipal water plant tank sampled after 8 years, flexural strength retention was 91%, far exceeding design expectations.

Conclusion

FRP water tank lining anticorrosion is a systematic engineering task requiring full-chain control from resin selection, fiber structure, construction environment, to inspection methods. Beijing Yuanhui FRP Co., Ltd. has successfully extended lining service life to over 20 years by optimizing vinyl ester resin formulations and ±55° winding processes. The industry should move beyond the misconception that “thicker coatings are better” and instead focus on interface bond strength and long-term chemical stability to truly solve tank corrosion problems.