Designing a tank for acid storage (like sulfuric, hydrochloric, nitric acid, etc.) is a special case due to the corrosive nature of acids, and it goes beyond standard API 650 in some ways.

Here’s a full breakdown for acid storage tank design, including API 650 and other international codes, with a focus on safety, materials, and corrosion resistance.

🧪 Acid Storage Tank Design – Overview

📘 Relevant Codes & Standards

Standard Region Notes

API 650 International OK for vertical atmospheric tanks, but needs supplemental corrosion considerations

API 652 USA Lining systems for tank bottoms (important for acids)

API 571 USA Corrosion mechanisms (useful for material selection)

BS EN 14015 Europe Steel tanks for atmospheric storage

ASME Section VIII Div 1USA / Global For pressurized or higher-stress acid tanks

ASTM D4097 / D3299USAFor FRP (fiberglass) acid tanks

UL 1316 / 142USAFor some chemical and underground tanks

ISO 6508, 11114InternationalFor hydrogen/acidic gas compatibility

📌 1. When API 650 Is Applicable

You can use API 650 if:

• The tank is atmospheric pressure

• You design conservatively for corrosion

• You select corrosion-resistant materials or linings

• You check compatibility using API 571 & API 652

But… for highly corrosive acids (like HCl, HNO₃, or high-concentration H₂SO₄), API 650 tanks require:

• Internal rubber lining

• Lead cladding, FRP lining, or thermoplastic liners

• Sometimes composite construction (e.g., steel + FRP inside)

🧱 2. Design Parameters for Acid Tanks

Parameter Description

Acid type H₂SO₄, HCl, HNO₃, acetic acid, etc.

Concentratione.g., 98% sulfuric acid behaves differently from 70%

Tank capacity Usually 5 m³ to 10,000+ m³

Temperature Impacts corrosion rate (especially for nitric acid)

Material compatibility Crucial – use charts from NACE / ASTM G31

Corrosion allowance Typically 3–6 mm (if unlined steel)

Vapor containment Some acids need scrubbers or vents with filters

Secondary containment Dikes or bunds (required by EPA/ISO/OSHA)

🧰 3. Material Selection

Acid Common Materials

Sulfuric Acid (H₂SO₄)Carbon steel (for >93%), 316L SS, FRP

Hydrochloric Acid (HCl) Rubber-lined steel, FRP, CPVC, PTFE

Nitric Acid (HNO₃)304L / 316L stainless steel, Alloy 20

Acetic Acid316L stainless steel, FRP

Phosphoric Acid316L, FRP, rubber-lined CS

For most acids, carbon steel alone is not suitable unless concentrations are very specific (like 98% H₂SO₄).

🧪 4. Lining & Coating (API 652)

• Rubber linings: Natural, neoprene, butyl rubber

• FRP liners: Vinyl ester resin-based

• Lead lining: For sulfuric acid in some legacy systems

• Thermoplastics: PP, HDPE, PVDF, PTFE (used in dual-laminate tanks)

🧮 5. Typical Design Using API 650 (Modified)

📏 Shell Thickness

Use standard API 650 hydrostatic calculations, then apply:

• Corrosion allowance: Often ≥3 mm

• Lining thickness: For internal coating (e.g., 6 mm rubber lining)

• Consider reduced allowable stress if lining or material is less ductile

🧯 Venting & Overpressure

• Use API 2000 for vent design

• Many acids release vapors, so use scrubbers or filter vents

💧 Secondary Containment

• Required by EPA 40 CFR or ISO 14001

• Bund height ≥110% of tank volume (typical)

🔩 6. Nozzles & Fittings

• Made from compatible material (e.g., PTFE-lined nozzles for HCl)

• Flanged joints preferred to avoid weld corrosion

• Overflow nozzle, vent nozzle, drain nozzle, level gauge, manway

• Consider splash guards, dip pipes, and neutralization pits

🧪 7. Inspection & Testing

Test Purpose

Hydrostatic Test100–110% full with water

Holiday Testing For lining continuity

Spark Testing For rubber/FRP liners

Visual Inspection  API 653 or local equivalent

Ultrasonic Thickness (UT)Monitor wall loss over time

✅ 8. Alternative: FRP Acid Tanks (ASTM D3299 / D4097)

For small to medium tanks (<75 m³), Fiberglass Reinforced Plastic (FRP) tanks are often:

• Cost-effective

• Highly corrosion-resistant

• Easily customizable

• Made per ASTM D3299 (filament-wound) or D4097 (contact-molded)

You can also use dual-laminate tanks:

• Outer shell: FRP

• Inner liner: Thermoplastic (e.g., PVDF, ECTFE)

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