Plastic Tank Calculation: Advanced Technical Guide for Precise Design and Analysis

Plastic tank calculation involves determining dimensions, volume, and structural integrity for safe storage. This article covers formulas, tables, and real-world examples.

Explore detailed methods for calculating plastic tank parameters, including thickness, capacity, and pressure resistance. Learn to optimize design efficiently.

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Calculate volume of a cylindrical plastic tank with 2m diameter and 3m height.
Determine wall thickness for a plastic tank holding 5000 liters under 1.5 bar pressure.
Find maximum allowable pressure for a rectangular plastic tank with 4mm wall thickness.
Estimate weight of a plastic tank made from HDPE with given dimensions and density.

Comprehensive Tables for Plastic Tank Calculation Parameters

Parameter	Common Values	Units	Description
Tank Diameter (D)	0.5, 1, 1.5, 2, 3, 4, 5	meters (m)	Diameter of cylindrical tanks, critical for volume and stress calculations.
Tank Height (H)	1, 2, 3, 4, 5, 6	meters (m)	Height of the tank, used to calculate volume and hydrostatic pressure.
Wall Thickness (t)	3, 4, 5, 6, 8, 10	millimeters (mm)	Thickness of the plastic wall, essential for strength and durability.
Material Density (ρ)	900, 950, 970, 980	kg/m³	Density of common plastics like HDPE, LDPE, PVC, affecting weight and stress.
Maximum Operating Pressure (P)	0.5, 1, 1.5, 2, 3	bar (1 bar = 100 kPa)	Pressure inside the tank, influences wall thickness and safety factors.
Allowable Stress (σ_allow)	8, 10, 12, 15	MPa	Maximum stress the plastic material can safely withstand.
Safety Factor (SF)	1.5, 2, 2.5, 3	Dimensionless	Factor to ensure design safety beyond calculated stresses.
Volume (V)	100, 500, 1000, 2000, 5000	liters (L)	Capacity of the tank, critical for storage requirements.

Fundamental Formulas for Plastic Tank Calculation

1. Volume Calculation

For cylindrical tanks, volume is calculated as:

Volume (V) = π × (D / 2)2 × H × 1000

Where:

V = Volume in liters (L)
D = Diameter in meters (m)
H = Height in meters (m)
Multiplying by 1000 converts cubic meters to liters.

2. Wall Thickness Calculation for Cylindrical Tanks

Using thin-wall pressure vessel theory, the minimum wall thickness t is:

t = (P × D) / (2 × σ_allow × SF)

Where:

t = Wall thickness in meters (m)
P = Internal pressure in Pascals (Pa) (1 bar = 100,000 Pa)
D = Diameter in meters (m)
σ_allow = Allowable stress of plastic in Pascals (Pa)
SF = Safety factor (dimensionless)

Note: Convert MPa to Pa by multiplying by 1,000,000.

3. Hydrostatic Pressure at Tank Base

Pressure due to liquid column height:

P = ρ_liquid × g × H

Where:

P = Pressure in Pascals (Pa)
ρ_liquid = Density of stored liquid in kg/m³
g = Acceleration due to gravity (9.81 m/s²)
H = Height of liquid column in meters (m)

4. Weight of Plastic Tank

Approximate weight based on volume of plastic used:

Weight = Surface Area × t × ρ_material

Where:

Surface Area = For cylinder: 2π × (D/2) × H + 2π × (D/2)² (m²)
t = Wall thickness in meters (m)
ρ_material = Density of plastic in kg/m³

5. Rectangular Tank Volume

For rectangular tanks:

V = L × W × H × 1000

Where:

L = Length in meters (m)
W = Width in meters (m)
H = Height in meters (m)

Detailed Explanation of Variables and Typical Values

Diameter (D): Commonly ranges from 0.5 m to 5 m for industrial tanks. Larger diameters increase volume but require thicker walls.
Height (H): Typically between 1 m and 6 m, height affects hydrostatic pressure and total volume.
Wall Thickness (t): Usually 3 mm to 10 mm depending on pressure and material strength.
Material Density (ρ): HDPE ~950 kg/m³, PVC ~1380 kg/m³, LDPE ~920 kg/m³.
Allowable Stress (σ_allow): Depends on plastic type and temperature; HDPE ~10-15 MPa at room temperature.
Safety Factor (SF): Typically 2 to 3 for plastic tanks to account for material variability and environmental factors.
Pressure (P): Internal pressure includes hydrostatic pressure and any additional pressure from pumps or gas.

Real-World Application Examples of Plastic Tank Calculation

Example 1: Cylindrical Plastic Tank for Water Storage

A cylindrical HDPE tank is designed to store 3000 liters of water. The tank diameter is 1.2 meters, and the height is to be determined. The allowable stress for HDPE is 12 MPa, and a safety factor of 2 is used. Calculate the required height, wall thickness for 1 bar internal pressure, and estimate the tank weight.

Step 1: Calculate Height

Using volume formula:

V = π × (D / 2)2 × H × 1000

Rearranged for height:

H = V / (π × (D / 2)2 × 1000)

Substitute values:

H = 3000 / (3.1416 × (1.2 / 2)² × 1000) = 3000 / (3.1416 × 0.36 × 1000) = 3000 / 1130.97 = 2.65 m

Step 2: Calculate Wall Thickness

Convert pressure to Pascals: 1 bar = 100,000 Pa

Convert allowable stress to Pascals: 12 MPa = 12,000,000 Pa

Using formula:

t = (P × D) / (2 × σ_allow × SF)

t = (100,000 × 1.2) / (2 × 12,000,000 × 2) = 120,000 / 48,000,000 = 0.0025 m = 2.5 mm

Recommended minimum thickness is 3 mm for manufacturing tolerance.

Step 3: Estimate Tank Weight

Calculate surface area:

Surface Area = 2π × (D/2) × H + 2π × (D/2)2

Surface Area = 2 × 3.1416 × 0.6 × 2.65 + 2 × 3.1416 × 0.6² = 10.01 + 2.26 = 12.27 m²

Wall thickness = 0.003 m, density of HDPE = 950 kg/m³

Weight = 12.27 × 0.003 × 950 = 34.98 kg

Example 2: Rectangular Plastic Tank for Chemical Storage

A rectangular tank made of PVC stores 1500 liters of chemical liquid with density 1200 kg/m³. The tank dimensions are 1.5 m length, 1 m width, and 1 m height. Calculate the hydrostatic pressure at the base, required wall thickness for 1.5 bar pressure, and approximate tank weight. Allowable stress for PVC is 15 MPa, safety factor 2.5.

Step 1: Verify Volume

Volume = L × W × H × 1000 = 1.5 × 1 × 1 × 1000 = 1500 liters (matches requirement)

Step 2: Calculate Hydrostatic Pressure

P = ρ_liquid × g × H = 1200 × 9.81 × 1 = 11,772 Pa = 0.1177 bar

Since operating pressure is 1.5 bar, use 1.5 bar for thickness calculation.

Step 3: Calculate Wall Thickness

Convert pressure and stress:

P = 1.5 bar = 150,000 Pa

σ_allow = 15 MPa = 15,000,000 Pa

Using rectangular tank wall thickness formula (approximate):

t = (P × L) / (2 × σ_allow × SF)

t = (150,000 × 1.5) / (2 × 15,000,000 × 2.5) = 225,000 / 75,000,000 = 0.003 m = 3 mm

Step 4: Estimate Tank Weight

Calculate surface area:

Surface Area = 2 × (L × W + L × H + W × H) = 2 × (1.5 × 1 + 1.5 × 1 + 1 × 1) = 2 × (1.5 + 1.5 + 1) = 2 × 4 = 8 m²

Wall thickness = 0.003 m, density of PVC = 1380 kg/m³

Weight = 8 × 0.003 × 1380 = 33.12 kg

Additional Considerations in Plastic Tank Design and Calculation

Temperature Effects: Plastic materials exhibit reduced strength at elevated temperatures; adjust allowable stress accordingly.
UV Exposure: Prolonged UV exposure can degrade plastics; consider UV stabilizers or coatings.
Chemical Compatibility: Ensure plastic type is compatible with stored liquid to prevent degradation.
Manufacturing Tolerances: Add margin to wall thickness to account for production variability.
Standards and Codes: Follow relevant standards such as ASTM D1998 for plastic tanks and API 650 for storage tanks.

Authoritative Resources and Standards for Plastic Tank Calculation

Summary of Key Points for Expert Plastic Tank Calculation

Accurate volume calculation is fundamental for capacity planning.
Wall thickness must be calculated considering internal pressure, allowable stress, and safety factors.
Material properties such as density and allowable stress vary by plastic type and temperature.
Hydrostatic pressure influences design, especially for tall tanks.
Weight estimation aids in logistics and structural support design.
Real-world examples demonstrate practical application of formulas and design principles.
Compliance with standards ensures safety and durability.

Mastering plastic tank calculation enables engineers to design efficient, safe, and cost-effective storage solutions tailored to specific industrial needs.