Designing Tank Manways, Platforms and Access Systems to AS1657 + API Requirements

How to Ensure Safe, Compliant, and Maintainable API 650 / API 653 Tanks in Australian Industrial Sites

Aboveground storage tanks (ASTs) are fundamental infrastructure across mining, manufacturing, agriculture, water treatment, and chemical processing industries. Whether storing process water, hydrocarbons, leach solutions, reagents, or slurry, these tanks must remain safe, accessible, and easy to maintain throughout their operational life.

While much engineering attention is placed on tank shells, foundations, nozzles, seismic design, and corrosion protection, the access systems — platforms, stairs, ladders, handrails, and manways — are just as critical. Poorly designed access is one of the most common sources of:

• Non-compliance

• Workplace injuries

• Difficult maintenance

• Re-certification failures

• Retrofits that cost more than getting it right the first time

In Australia, access systems for tanks must comply with AS1657 (Fixed platforms, walkways, stairways and ladders) as well as API 650 / API 653 and local regulations.

This article explains how to design manways and access systems that are safe, compliant, and practical — and how engineered solutions from Trang Imagineering help asset owners reduce risk and lifecycle cost.

Why Access Systems Matter for API Tanks

API 650 tanks are large-volume, long-service-life structures. Safe entry and access are required for:

• Internal inspections

• API 653 assessments

• Cleaning operations

• NDT activities (UT, MT, PAUT, visual inspection)

• Agitator maintenance

• Vent, nozzle and roof upkeep

• Sampling and quality control

• Emergency access

Without properly designed manways, ladders, platforms and handrails, operators face unnecessary hazards — and regulators will not sign off on installations.

Governing Standards: What Applies?

Tank access systems must comply with multiple overlapping standards. The most common are:

AS1657:2018 – Fixed platforms, walkways, stairways and ladders

Covers:

• Ladders (caged, uncaged, rung spacing, clearances)

• Stairways (angles, risers, treads)

• Platforms (size, load rating, kickplates)

• Handrails and guardrails

• Fall protection requirements

• Minimum widths and ergonomic rules

Any platform, landing, ladder or stair around an API tank must comply with AS1657.

API 650 – Welded Tanks for Oil Storage

Provides requirements for:

• Roof manways (location, size, reinforcement)

• Shell manways (types, sizes, reinforcement plates)

• Access to and around appurtenances

• Safety considerations for roof types (cone, pontoon, floating roof)

• Ladder brackets, wind influences, and anchorage

• Live load requirements on platforms and roofs

API 650 is not an access standard, but it defines tank-specific structural rules that designers must follow when attaching access systems.

API 653 – Tank Inspection, Repair, Alteration, and Reconstruction

Relevant when:

• Designing manways for tanks with expected repairs

• Ensuring access is sufficient for future inspections

• Maintaining safety during entry and repair works

• Upgrading or retrofitting non-compliant older tanks

API 653 implicitly reinforces AS1657, because unsafe or inadequate access often leads to inspection non-compliance.

WHS Act, WHS Regulations & Local Site Requirements

These always apply and override “minimum engineering.”
Safe access must consider:

• Fall protection

• Confined space entry

• Emergency egress

• Lighting and slip hazards

• Site-specific permit systems

Designing Manways for API Tanks

Manways are critical for entry and maintenance. Poor design makes internal inspection dangerous or impossible — and many tanks in Australia require manway retrofits due to non-compliant access.

1. Shell Manways

API 650 typically uses:

• 600 mm (24-inch) shell manways

• Reinforcement plates sized per Appendix 1

• Correct nozzle neck length and weld prep

• Proper positioning above the tank bottom

Key design considerations:

Positioning

• Must not interfere with stiffeners or wind girders.

• Should allow ergonomic entry (avoid placing behind pipework).

• Consider pump suction lines, bund access, and nearby structural elements.

Safety

• Install AS1657-compliant platforms if manway is > 2 m above ground.

• Include handrails, gates, and fall-arrest anchor points if required.

• Ensure adequate lighting for confined-space entry.

Maintenance

• Hinged covers reduce manual handling risk.

• Ensure clearance for davits, lifting slings, tripods.

2. Roof Manways

API 650 requires:

• Minimum sizes depending on roof type

• Reinforcing pads

• Placement that avoids roof structural members

• Clear access routes

Design considerations:

• Roof slope affects safe walking and rail installation.

• Internal mixers, vents, and foam systems obstruct access — plan platforms accordingly.

• For floating roof tanks, walkways must allow safe movement across pontoons.

Designing Ladders, Platforms and Stairways to AS1657

AS1657 governs the details of safe access — and it is very specific. Below are essential design requirements.

1. Ladders

Ladder Types

• Vertical ladders (with or without cages)

• Inclined ladders

• Ship ladders (steeper stair-like access)

Requirements

• Rung spacing: typically 300 mm

• Side rail spacing: 375–525 mm

• Clearances behind rungs: ≥ 200 mm

• Cages required above certain heights unless fall arrest is used

• Landing platforms required every 6–10 m (depending on configuration)

Tank integration considerations

• Ladders must be structurally attached to shell or to independent support frames.

• Avoid welding excessive ladder brackets directly to thin shell plates — may require reinforcement pads.

• Wind loading on tall external ladders must be assessed.

2. Platforms and Landings

AS1657 requires:

• Minimum width (usually ≥ 600 mm; often 800 mm for industrial sites)

• Guardrails at 900–1100 mm height

• Toe boards / kickplates (≥ 100 mm)

• Load rating per AS1657 and AS1170

• Slip-resistant flooring

• Access gates that auto-close at ladder interfaces

Tank-specific platform challenges:

• Curved shell surfaces require custom brackets.

• Uneven settlement of tank foundations can affect platform levels.

• Bund walls may block traditional access — requiring spanning structures or stairs.

3. Stairways

Stairways are safer and preferred for frequent access.

Key AS1657 requirements:

• Inclination: 20°–45°

• Uniform risers (150–225 mm typical)

• Tread depth (250–300 mm typical)

• Continuous handrails

• Midrails or mesh infill

• Non-slip surfaces

When to choose stairs instead of ladders:

• Frequent access to roof manways

• Operators carrying tools

• Tanks with high roofs (> 12 m)

• When site safety standards exceed minimum AS1657 requirements

Structural Engineering Considerations

Designing access systems is not just a matter of bolting on prefabricated stairs. Proper engineering considers:

✔ Differential thermal movement between tank and access structures

Especially relevant for:

• Heated tanks

• Tanks with differential sunlight exposure

• Cryogenic or very cold environments

✔ Wind actions on external platforms and ladders

Tall tanks with 360° wind exposure require:

• Wind bracing

• Stiffeners

• Load path verification

✔ Load paths into the shell

Tank shells are thin — typically 6–12 mm on smaller tanks; even large tanks may have thin upper courses.
Platforms must transfer load without causing local buckling.

✔ Settlement

Tank foundations often experience long-term settlement.
Access systems may need accommodation for:

• Slip joints

• Adjustable supports

• Independent foundations

Common Mistakes in Tank Access Design

These errors lead to non-compliance, safety risks, or costly retrofits:

❌ Welding heavy platform brackets directly to thin shell plates

→ Causes shell distortion, stress concentrations, buckling.

❌ Ignoring AS1657 clearances and ergonomics

→ Operators cannot safely climb or manoeuvre.

❌ Using generic ladder kits not designed for tanks

→ Incorrect inclination, non-compliant rung spacing, inadequate handrails.

❌ Poor manway placement

→ Obstructed access, unsafe entry angles, limited ability to manoeuvre equipment.

❌ No consideration for future API 653 inspections

→ Inspectors struggle; tank requires rework later.

How Trang Imagineering Helps

Trang specialises in practical, code-compliant, fabrication-ready engineering for tanks across mining, agriculture, water treatment, and heavy industry.

Here's how we add value:

1. AS1657-Compliant Access System Design

We design:

• Ladders

• Spiral stairs

• Platforms

• Landings

• Handrails

• Roof walkways

• Gates and fall-arrest systems

Everything is engineered to meet AS1657, site standards, and operational needs.

2. API 650 / API 653 Integration

Trang ensures all attachments, reinforcements and structural interfaces comply with:

• API 650 Appendix 1 (reinforcement requirements)

• Roof structural limits

• Shell thicknesses and allowable loads

• Nozzle and manway interactions

• Wind girder location and allowable modifications

We prevent distortions, overstress, and non-compliant weld details — saving costly rework.

3. FEA for Complex Attachments

Where loads or geometry are complex, we provide:

• Local shell stress modelling

• Bracket optimisation

• Wind and vibration analysis

• Buckling checks

• Settlement impact analysis

This is especially useful for large platforms or tall external stair towers.

4. Fabrication-Ready Drawings

Clear, practical drawings reduce workshop downtime, eliminate ambiguity, and ensure:

• Simple, efficient fabrication

• Correct materials and profiles

• Fewer RFIs during construction

• Fast, clean site installation

5. Retrofitting Older Tanks

Many NSW mining sites have older tanks that:

• Pre-date AS1657

• Have non-compliant ladders

• Lack safe platforms

• Have corroded or overloaded connections

Trang provides retrofit solutions that bring assets back into compliance — without excessive cost.

6. Full Lifecycle Support

From concept through design, installation and API 653 inspection cycles, Trang supports safe access for decades of service.

Safe, Compliant Access Systems Are Non-Negotiable

Designing access systems for API tanks is far more than adding ladders and platforms.
It requires:

• A deep understanding of AS1657

• Practical experience with API 650 / 653

• Awareness of site operations

• Structural engineering knowledge

• Consideration of lifecycle maintenance and inspection

Trang Imagineering delivers engineered solutions that ensure:

• Safe access

• Full compliance

• Long service life

• Minimal rework

• Reduced inspection difficulty

• Lower whole-of-life costs

If you need access upgrades, new tank designs, or verification of existing systems, Trang can help.