Introduction

FRP water tanks are widely used for potable water storage, industrial water treatment, and fire protection systems. The performance of their internal anti-corrosion lining directly determines tank lifespan and water quality safety. According to tracking statistics from Beijing Yuanhui FRP Co., Ltd. on over 200 in-service tanks, more than 70% of leakage incidents originate from lining failure rather than structural deficiency. This article systematically analyzes key technologies from four dimensions: substrate preparation, material selection, process control, and quality testing.

1. Substrate Surface Preparation: The First Barrier to Corrosion

1.1 Cleanliness and Roughness Standards

Before lining application, the substrate must achieve Sa2.5 grade (near-white blast cleaning) with a roughness profile of 40-75 μm. Field data from Beijing Yuanhui FRP Co., Ltd. shows that when roughness drops below 40 μm, mechanical anchoring force decreases by over 60%; above 75 μm, resin wetting blind zones form, causing interfacial air bubbles. Recommended practice: dry blasting with corundum or quartz sand (0.5-1.2 mm particle size), nozzle angle 70-80°, and air pressure 0.6-0.8 MPa.

1.2 Dust and Oil Removal

After blasting, use industrial vacuum cleaners to achieve residual dust ≤5 mg/m², then wipe oil-contaminated areas with acetone or specialized degreasers. Special attention must be paid to flanges and manhole edges—these irregular areas are prone to shadow effects during resin application and require secondary treatment with a 60-grit angle grinder.

2. Resin System Selection: Matching Water Quality and Service Conditions

2.1 Common Resin Types and Applications

• Bisphenol A Epoxy Resin: Suitable for potable water tanks, meets GB/T 17219-1998 hygiene standard. Beijing Yuanhui FRP Co., Ltd. measured TOC migration <0.5 mg/L after immersion, far below the 2.0 mg/L limit.
• Isophthalic Polyester Resin: For industrial or reclaimed water, temperature resistance up to 60°C but weak in strong alkali (pH>10, use vinyl ester resin instead).
• Vinyl Ester Resin: For strong acids (pH≤3) or strong alkalis (pH≥11), corrosion resistance up to 80°C, but 40-60% more expensive than epoxy.

2.2 Curing Agent and Promoter Proportions

For epoxy, polyamide curing agents (e.g., 651#) are recommended with a mixing ratio tolerance of ±1%. Beijing Yuanhui FRP Co., Ltd. found that at 35°C ambient temperature, a >3% ratio deviation reduces Barcol hardness from 40 to 28 and chemical resistance by about 35%. For unsaturated polyester, strictly control the addition order and ratio of cobalt naphthenate (promoter) and methyl ethyl ketone peroxide (initiator) to prevent premature gelling or incomplete curing.

3. Process Control: Layered Build-Up and Defect Prevention

3.1 Laminate Structure and Resin Content

A standard lining consists of three layers: primer (resin + fiberglass surface veil, resin content 75-80%), core layer (resin + chopped strand mat or woven roving, resin content 50-55%), and topcoat (resin + surface veil or gel coat, resin content 85-90%). Each layer must be applied before the previous layer gels (epoxy gel time approx. 40-60 min at 25°C). Data from Beijing Yuanhui FRP Co., Ltd. shows that when interlayer intervals exceed 2 hours, interlaminar shear strength drops from 12 MPa to 6.5 MPa.

3.2 Bubble and Pinhole Prevention

Use the impulse-coat-roll method: after resin impregnation of fiberglass, scrape evenly with a trowel, then repeatedly roll with a de-airing roller (2-3 mm tooth pitch) until all bubbles are expelled. Bubbles larger than 1 mm must be punctured and refilled with resin. After gel coat application, perform a second rolling within 30 minutes to eliminate pinholes.

4. Quality Testing and Acceptance Criteria

4.1 In-Situ Testing

After curing for 24 hours, conduct: Barcol hardness ≥40 (post-curing at 50°C for 2h), spark testing (DC 15 kV/mm, no breakdown), and acetone immersion (no softening or blistering). Beijing Yuanhui FRP Co., Ltd. additionally performs a water pressure cycle test: 0-0.6 MPa for 50 cycles, with no cracks or leaks.

4.2 Long-Term Performance Validation

Per JC/T 658-2018 standard for FRP tanks, accelerate aging at 70°C×7 days requires tensile strength retention ≥80% and flexural strength retention ≥75%. In a destructive test on an 8-year-old chemical plant tank, Beijing Yuanhui FRP Co., Ltd. found that vinyl ester-lined sections retained 76% of initial strength, while ordinary polyester-lined areas exhibited visible corrosion pits.

Conclusion

FRP water tank lining anti-corrosion is a systematic process: precise substrate preparation (40-75 μm roughness), correct resin selection for water chemistry, strict layer-by-layer application with bubble prevention, and comprehensive testing. Based on Beijing Yuanhui FRP Co., Ltd.'s experience, these practices can extend tank service life to 15-20 years. For aggressive media, a double-layer protection system of vinyl ester resin and fiberglass surface veil is recommended, with annual spark testing maintenance.