Loading Plan for Methyl Acetate: Drum Count, Flexitank and ISO Tank Payload Math

Load planning for methyl acetate (CAS 79-20-9; UN 1231, Class 3, packing group II) is governed by density at 20 °C of 0.932 kg/L, a flash point of −10 °C, a boiling point of 56.9 °C, and a vapour pressure of approximately 23.1 kPa at 20 °C. The liquid is a fast-evaporating, low-viscosity polar solvent that forms flammable mixtures with air; the closed-cup flash point and boiling point place it in packing group II under ADR Part 2 because the flash point is below 23 °C and the boiling point is above 35 °C. Density is the controlling payload variable. At 0.932 kg/L, each 1,000 L of liquid volume contains 932 kg net mass. Ullage, thermal expansion, and pressure-relief behaviour therefore govern the loading plan for 200 L steel drums, flexitank units, and ISO tank containers.

How Many 200 L Drums Are Required for a 20,000 kg Shipment?

For a 200 L UN 1A1 tight-head steel drum with an internal epoxy phenolic lacquer, the planning fill volume is reduced from nominal capacity to 180 L at 20 °C. The 20 L ullage maintains a 90% liquid filling degree and prevents hydraulic pressure build-up if the drum interior reaches 50 °C in transit. At 0.932 kg/L, 180 L contains 167.8 kg net methyl acetate. A 20,000 kg order therefore requires 119.2 drums; rounding up provides 120 drums, yielding 20,136 kg net. If the packaging is certified at a fixed 180 kg net charge per drum, the count is 112 drums and the net mass is 20,160 kg. The ullage-based value is the conservative planning baseline because ADR 4.1.1.4 requires sufficient outage to accommodate thermal expansion without permanent distortion or leakage.

Drum loading is executed through a 50 mm stainless steel lance with bottom filling or dip-tube filling to reduce splash charging. A grounding clamp with resistance not exceeding 10 Ω is applied in accordance with NFPA 77. The fill stop is set at 180 L per drum, and the bung seals are checked for methyl acetate compatibility. Drums are then palletized with secondary containment and labelled as UN 1231, Class 3, PG II.

Flexitank arithmetic for methyl acetate is a hypothetical planning exercise rather than an operational loading method because the cargo is a Class 3, packing group II flammable liquid. Standard flexitank approvals under the Container Owners Association Flexitank Code and general provisions of the IMDG Code are limited to non-dangerous liquids; no generalized competent authority authorization exists for UN 1231 in a single-use flexible bladder. For the calculation case only, a nominal 24,000 L flexitank filled to 95% of capacity at 20 °C would contain 22,800 L, equivalent to 21,249.6 kg net. Using a cubical expansion coefficient of approximately 1.3 × 10⁻³ K⁻¹, that fill volume expands to 23,689 L at 50 °C, corresponding to 98.7% of nominal capacity. The remaining 1.3% ullage is insufficient for the vapour pressure rise and thermal expansion of a liquid with a boiling point of 56.9 °C. A flexitank load plan for methyl acetate is therefore not accepted under ADR 4.1 or IMDG Code package and portable tank provisions unless a special competent authority approval is issued. Published data for this specific configuration is limited.

ISO Tank Payload Math for Methyl Acetate at 0.932 kg/L

An ISO 1496-3:2019 20 ft tank container with a nominal shell volume of 24,000 L and a maximum gross mass of 30,480 kg is typically tare-rated between 3,550 kg and 4,200 kg, leaving a legal payload capacity of 26,280 kg to 26,930 kg. Methyl acetate is volume-limited before mass-limited in this equipment class. The ADR 4.2.1.9.1 degree-of-filling rule for a flammable liquid requires the initial fill to be set so that the liquid does not exceed the specified maximum filling degree at 50 °C. Using a cubical expansion coefficient of approximately 1.3 × 10⁻³ K⁻¹, the fill at 20 °C is set at approximately 90.5% of nominal volume. At 21,720 L, the net payload is 20,243 kg, and the ullage is 2,280 L. The mass is below the legal payload capacity, confirming that the tank is volume-limited rather than mass-limited.

Bottom loading is performed through a 76 mm bottom-loading arm with vapour return. The fill rate is initially set at 150 L/min until the liquid covers the inlet, then increased to 600 L/min. At 600 L/min, the linear velocity in a 76 mm pipe is approximately 2.2 m/s, below the 7 m/s static-accumulation threshold commonly applied for intermediate-conductivity solvents. The pressure-relief valve set point is verified before loading; for many Class 3 PG II tank containers, the relief valve is set at 4.4 bar. The tank interior is inspected for residual water because methyl acetate can hydrolyse to acetic acid and methanol. Water content in the cargo is typically controlled below 0.1% by mass to limit acid generation and carbon steel corrosion during transit.

When ADR/RID Loading Limits Force Ullage Recalculation for Methyl Acetate

Because methyl acetate has a boiling point below 60 °C, the load plan must be recalculated for summer routes where the container interior can exceed 40 °C. If the initial fill at 20 °C is 21,720 L, a thermal excursion to 50 °C increases the liquid volume to approximately 22,566 L, corresponding to 94.0% of the 24,000 L shell volume. If the routing data predicts a 55 °C interior, the initial fill must be reduced to maintain the maximum allowable filling degree at that higher temperature; this lowers the load plan by approximately 1.3% per 5 °C increment. For short European routes with controlled temperature, operators may apply a fill up to 91.0% only after written verification against ADR 4.2.1.9.1. The pressure-relief valve is an independent safety element and does not permit additional liquid fill beyond the regulatory ullage.

Before loading the ISO tank, the operator verifies the pressure-relief valve set point, checks the bottom outlet valve position, and connects a 10 Ω grounding clamp. The vapour return line is opened before starting the pump to prevent the tank from being pressurised during loading. The fill stop is set at 21,720 L based on the ullage calculation. After loading, the outlet valve is locked closed, the vapour return is isolated, and the tank is weighed on a calibrated weighbridge to confirm net mass. The measured mass is compared with the volume-metered figure; a deviation exceeding 0.5% triggers re-inspection because it may indicate water bottoms or a calibration fault in the loading meter.