Converting a line from steel strap to PET: an engineering checklist

Steel strap remains the standard choice for many heavy and hot loads. In 2025 there were extra reasons to ask whether some steel lines could move to polyester (PET). In the US, Proclamation 10947 raised the Section 232 duty on steel articles to 50% from 4 June 2025, which changed the landed cost of imported steel strap. Elsewhere the familiar arguments apply: handling weight, cut risk and the cost of stocking strap, seals and spare tools.

A conversion is an engineering change to the packing system, not a substitution on a price list. This checklist sets out what to decide before the first PET coil reaches the line.

Step 1: confirm that the load suits PET

A strapping guide published by the distributor Spicers in November 2024 summarises the trade-off. It describes steel as the standard for medium to heavy loads, with high column strength and resistance to high temperatures, but notes that its lack of elasticity can let straps loosen on loads that settle or shrink, such as lumber. Polyester, by contrast, keeps the load compressed after settling and holds its tension in transit. Sharp product edges are a separate question: plastic strap needs protection wherever it crosses one.

Answer these questions before going further:

• Is the product hot when strapped, or exposed to high temperatures in storage or transport?
• Must the strap cross sharp metal edges, and can edge protection be added where it does?
• Does the load settle, compress or dry out after strapping?
• Will strapped units be stored outdoors, and for how long?
• Is the strap used only to unitise the load, or is it relied on in a transport securing arrangement?
• Is the unit ever lifted by its straps? If so, stop: lifting needs its own engineering review, not a strap substitution.

If the answers point to heat or to sharp edges that cannot be protected, keep that line on steel and look for conversions elsewhere. Resist the shortcut of comparing one breaking-strength figure with another: steel stretches little once sealed, while PET elongates and recovers, so two straps with similar breaking strength can behave quite differently on the same load.

Step 2: document the steel system you are replacing

Record the steel strap width and thickness, its finish, the seal type and profile, the sealer or combination tool, and the number and position of straps on each unit. ASTM D3953 is the specification for flat steel strapping and seals that many purchasing documents refer to; note whether your current orders cite it. This record is the baseline for the trial and the fallback if the trial fails.

Step 3: define the PET system as a whole

Steel system element	PET decision to make
Strap width and thickness	PET width, thickness, embossing and grade, using the strap maker’s data
Seal and sealer	Friction weld, or a sheet metal clip with a matched crimping tool
Tensioning tool	Manual or battery-powered tool designed for plastic strap
Edge protection	Corner protection suited to PET at the agreed tension
Dispenser	A dispenser sized for the PET coil
Specification reference	ASTM D3950 covers nonmetallic strapping and joining methods

Tools built for steel strap are not a substitute for tools designed for plastic strap, so budget for new tensioners, sealers or friction-weld tools and their spare parts. The joint matters as much as the strap. The strength of a joint relative to the strap’s breaking strength, usually called joint efficiency, depends on the strap, the closure or weld and the tool working together. Do not transfer a strap’s breaking strength to its joint.

Step 4: run a controlled trial

1. Choose representative loads, including the heaviest and the most awkward.
2. Fix the PET specification, joint method, tool settings and strap positions in writing.
3. Strap trial units on the production line with trained operators, not only in a test bay.
4. Inspect the units after strapping, after the first handling, after storage and on arrival at the customer.
5. Agree the acceptance criteria beforehand: no slack straps, no joint failures, no damage at edges.
6. If joint performance evidence is required, define the test method and who performs it.

Keep steel on a comparison group of the same loads during the trial. Without a control, a good result may simply reflect a quiet shipping month.

Step 5: safety, training and stock

Steel strap cut under tension can spring back: an Oregon Department of Transportation safety talk from 2009 warns that cut bands can lash out as the tension is released, and steel edges cut. PET reduces those particular hazards, but the strap is still under tension and still needs proper cutters and a cutting procedure. Train operators on the new tool, the joint check and safe cutting. Plan the run-down of steel strap and seals, so that the two systems are not mixed on the same line and old seals are not used on the wrong strap.

Step 6: check the plastic packaging rules

In the UK, Plastic Packaging Tax rose to £223.69 per tonne from 1 April 2025 for plastic packaging containing less than 30% recycled plastic, as CIEH reported in November 2024. If your business imports PET strap into the UK, ask your adviser whether those imports bring you within the tax and what evidence of recycled content you need from the supplier.

In the EU, Regulation (EU) 2025/40 sets a minimum of 35% recycled content for plastic packaging outside the contact-sensitive categories, from 1 January 2030 or later. Ask PET strap suppliers how recycled content is stated, measured and verified.

Step 7: roll out line by line

Convert one line, review it after a full cycle of normal shipments, then move to the next. Update work instructions, purchase specifications and spare-part lists at each step, and remove obsolete steel items from the reorder list only when the last steel line has changed.

Keep both systems specified

For lines moving to PET, the PET strap and sheet metal clip pages list the dimensions to agree; for lines staying on steel, the steel strapping seal page does the same. Describe the load, the current system and the proposed change through the enquiry page. Strength values remain on request.