Tank Lining — Chemical-Resistant Internal Coatings: Epoxy Novolac vs Vinyl Ester per API 652 / NACE

Storage tanks — acid, alkali, oil, fuel, water, chemicals — corrode "from the inside" continuously while holding liquid, far harsher than external corrosion. Ordinary external anti-rust paint cannot be used for immersion — it requires a dedicated tank lining (chemical-resistant internal coating).

This article explains lining types, selection by chemical, surface prep, holiday testing, and the API 652 / NACE standards.

1. Why Immersion Is Harsher Than the Exterior

flowchart TD
  A[Steel surface inside tank] --> B[Submerged in liquid continuously
immersion service]
  B --> C[Chemical permeation]
  B --> D[High concentration + temperature]
  B --> E[Abrasion from agitation/flow]
  C --> F[Needs special chemical-resistant resin
+ thicker + 100% holiday test]
  D --> F
  E --> F

• Permeation — chemicals diffuse through the film to the steel if the lining is thin/wrong type
• Concentration + temperature accelerate corrosion
• A single pinhole = liquid reaches steel = perforating corrosion

2. Lining Types — Choose by Chemical

Choose by the manufacturer's chemical resistance chart against the actual chemical + concentration + temperature.

3. The Heart — Surface Prep + Holiday Test

• Immersion surface prep is more rigorous — abrasive blast Sa 2.5+ and correction of surface imperfections (sharp edges, welds, porosity) per NACE SP0178
• 100% holiday test (NACE SP0188) — inspect the whole surface for pinholes with a high-voltage spark (thick linings) or wet sponge (thin linings) — one holiday fails it
• DFT per lining spec (immersion needs more thickness than atmospheric work)

Unlike external work which tolerates minor imperfections — immersion must be 100%.

4. Standards

• API 652 — lining of aboveground oil-storage tank bottoms
• NACE SP0178 — surface prep/weld detailing for immersion lining
• NACE SP0188 — holiday/discontinuity testing
• ISO 12944 (Im category) — immersion · NACE SP0181 — internal coating

5. Tank Lining Spec Checklist

1. State chemical + concentration + temperature in the tank (sets the lining choice)
2. Select the resin from the chemical resistance chart (novolac/vinyl ester)
3. Specify surface prep (Sa 2.5+, correct surface imperfections per NACE SP0178)
4. Specify DFT + 100% holiday test (NACE SP0188)
5. Food/drinking water → certified lining for food/water contact

We supply and coordinate chemical-resistant tank linings — epoxy, epoxy novolac (concentrated acids), vinyl ester (aggressive chemicals/high temperature) to API 652 / NACE SP0178 / SP0188 — with guidance on selecting the resin by actual chemical + temperature, immersion surface prep, and 100% holiday testing for acid/fuel/water/food tanks.

Talk to our engineering team to select a lining system that fits your chemicals — call 02-096-2118 or LINE OA @sahawatt1988.

Summary

• Tank lining ≠ external paint — immersion is harsher (permeation + concentration + temperature + abrasion)
• Epoxy novolac (concentrated acids ~95-130°C) · Vinyl ester (broad acids/alkalis/solvents, high temp)
• Choose by the chemical resistance chart (chemical + concentration + actual temperature)
• Surface prep Sa 2.5+ (NACE SP0178) + 100% holiday test (SP0188) — a single pinhole fails
• Standards: API 652 / NACE SP0178 / SP0188 / ISO 12944 Im

The right lining type + complete holiday testing = no tank leaks/contamination, where repair + downtime cost many times more.