There is a tempting answer to this – a number of trips – and it would be dishonest to give one, because the spread between a well-run closed loop and an open pool is not a factor of two, it is closer to an order of magnitude. What is useful instead is knowing what ends a crate, because the end is almost always one of four things.
Fatigue at the stress points
Crates do not wear out evenly. They fail at corners, at handle roots and at the points where the rim meets the wall – the places that flex every time the crate is loaded and unloaded. A crate that looks fine overall can have hairline cracking at a handle root, and that is a crate near its end.
Inspecting for this is quick and it is the single best predictor of a batch failing together. When one crate in a batch shows it, the rest are the same age and will follow within weeks.
Cold plus impact
Polypropylene loses impact strength as temperature falls, and the effect starts well inside chilled-storage range. A crate that shrugs off being dropped at ambient will crack in a cold room. If your crates go into a chiller and are handled there, this is the likely end, and the fix is an impact-modified resin chosen at the time of order. We wrote about this specifically in why PP crates crack in cold storage.
Ultraviolet
Crates left in a yard chalk and embrittle. It is slow and then it is sudden – a crate that looked acceptable last month breaks on the first knock this month. Stabilised grades cost a little more and are worth it if crates spend real time outdoors. If they do not, the additive is money spent for nothing.
Loss, which is not a durability problem
In an open pool, the dominant reason a crate stops making trips is that it stopped coming back. Crates leave on one-way shipments, sit in a grower’s yard over a season, or get taken for something else. This is usually a larger number than breakage, and it is a logistics problem that no resin choice addresses.
It is also the thing to measure first. If your attrition is mostly loss, spending more on a tougher crate is the wrong investment.
Getting your own number
Mark a batch by colour or by a date tag and count returns after a season. That is your trip life, measured under your conditions. Any number a supplier gives you – ours included – is an estimate made without your yard, your cold room and your drivers.
Repair, and the point at which to stop
A cracked crate can sometimes be welded, and for a crate with a clean split away from a load path it is worth doing. What is not worth doing is welding a handle or a corner – both are stress concentrators and a repair there is weaker than the original.
The decision rule we would suggest: repair if the damage is in a flat panel, replace if it is at a corner, a handle root or a stack rim. Following that keeps the fleet predictable, and a predictable fleet is worth more than the crates saved by patching everything.
What we can do
We make PP crates for fruit and vegetables and will specify resin and wall thickness from your loop rather than from a standard. Tell us whether crates are handled cold, whether they sit outside, and whether the loop is closed, and we will tell you honestly what to expect – including when a cheaper crate is the right one to buy.