Twelve hundred and forty 4140 piston rods left Yantian on 4 July and reached Rotterdam on 14 August. Forty-one days door to door, nine days longer than the transit we had quoted. On 17 August their incoming inspector opened crate four and found rust.
One hundred and eighteen pieces out of 1,240. Not a light film you can wipe off with a rag. Orange-brown patches along the ground journal, a ring of it where the part sat in the foam nest, and pitting in the corners of the wrench flats that you could catch with a fingernail.
I have packed a lot of parts for sea freight and I still got this wrong. Here is the whole failure, what it cost, and the four changes that stopped it.
The parts
4140 pre-hardened bar, 28 to 32 HRC as received, turned and then ground to Ø32 h6 over a 410 mm length. Journal surface 0.4 µm Ra, two wrench flats milled at the tail end, one Ø8 cross-hole through the head for a retaining pin. Twenty pieces per plywood crate, twelve crates, 1,240 pieces. The PO was priced at USD 38 each, which is a budget estimate for that size and finish in 4140 rather than a market number. Anyone who needs a firm figure sends us the drawing and our team confirms it within one business day.
What we assumed, and why it was wrong
My first call was the film. We buy 50 µm VCI film from a local converter and it has never let us down on shorter routes. I asked for the lot number and the certificate, expecting a bad batch. The film was fine. It was 19 months old, which matters and I will come back to it, but the film was not why those parts rusted.
They rusted because of three decisions we made in the last two hours before the crates were closed.
One: we packed warm parts with water still inside them
The last operation was a wash in an aqueous cleaner followed by a hot-air dry. That dry cycle ran 12 minutes at 70 °C, which is enough for a flat face and not enough for a Ø8 blind cross-hole. The floor that afternoon was 31 °C at 82% relative humidity, which is an ordinary Shenzhen July and exactly the condition where a hole that looks dry is not. VCI film works by saturating a closed headspace with inhibitor vapour. If that headspace already holds water vapour, the inhibitor competes with it and loses. We wrapped 1,240 parts with something close to half a gram of rinse water sealed inside each cross-hole.
Two: the crates were not sealed
We vent crates for customs inspection, 30 mm gaps on two sides, because we have had a crate opened with a crowbar before and the parts inside were damaged worse by the inspection than by the voyage. Those gaps are good for the inspector. They are fatal for vapour-phase protection. VCI needs an enclosed volume to hold concentration, and a vented crate is a chimney. The inhibitor left the box inside the first week, and for the remaining 34 days those parts had nothing protecting them except film where film happened to touch steel, and humid air everywhere else.
Three: the desiccant was sized for the wrong transit time
Our packaging sheet called for four 100 g desiccant bags per crate, which is right for 30 days. Actual transit ran 41 days, including a nine-day dwell in Singapore waiting for a berth. Then add container rain. A steel box on deck swings from 34 °C in the afternoon to 12 °C at night, the air inside gives up its moisture on the ceiling, and it drips onto whatever sits underneath. Four bags were never going to hold that. The calculation should have been done against 45 days with a margin, and it should have been done per cubic metre of crate volume rather than per crate.
What it cost
We sent an inspector to Rotterdam instead of flying the lot back, because return freight would have doubled the loss. Nine pieces carried pits deeper than the 0.02 mm we could remove by re-grinding and were scrapped. The other 109 were stripped, re-ground 0.02 mm under nominal, re-inspected and re-packed at USD 6.40 each. Air freight on the reworked and replacement pieces, 210 kg, came to USD 1,480. The customer’s own sorting time was USD 450 and we paid it. Overtime to pull the rework forward added USD 620. Total USD 3,590 against a PO worth USD 47,120, so about 7.6% of the order, plus a quality record with that customer that took two more shipments to clean up.
The four changes
Every blind hole and cross-hole now gets a 20-second blow-out with dry air at 6 bar, then 15 minutes in a 60 °C oven, then it cools in a covered tray. Nothing gets wrapped warm. The rule is crude and it works: if you can feel heat through your glove, it is not ready to pack.
The VCI film is gone for sea freight. Each crate now takes a heat-sealed aluminized barrier bag with a VCI emitter inside, and the bag is sealed after most of the air is pushed out. The crate vents stay for customs, but they sit outside the bag. The bag is the enclosed volume now. The crate is just the box.
Desiccant is calculated per cubic metre for a stated transit time with a 30% margin, and the number is printed on the packing list. Twelve 100 g units for a 1.2 m³ crate over 45 days is what we run today. A longer route changes the number and somebody has to sign it.
Film and bag stock is FIFO with a 12-month use-by date, kept in a sealed bin rather than on an open shelf beside the wash station. Nineteen months on a humid shelf is not the same product as nineteen months in a sealed bag, and the film that failed us had spent its life in the first condition.
The check that would have caught it
We now pull three pieces from the first packed crate of every sea shipment and run them 72 hours at 40 °C and 90% relative humidity in a small chamber before the container is released. It costs half a day and roughly USD 30 in labour. If the sample rusts, the crate gets re-packed. Four shipments since September, 3,900 pieces, zero rust claims. The new packaging adds USD 0.42 per piece, again a budget estimate, against USD 3,590 of rework on one lot.
If you are buying parts that travel by sea
Ask what the packaging spec assumes for transit days, and ask whether the crate is sealed or vented. Those two answers tell you more about whether your parts will arrive clean than any brand name printed on the rust-preventive. If your supplier cannot state a desiccant quantity and a transit assumption, they are packing by habit and hoping.
The material side of this job sits on our 4140 steel page, and the finish that matters here is under surface grinding. The packaging rules we now work to are written up in packaging for export, and shipping and Incoterms covers who owns the risk once the container closes. If you want the cost side first, the instant quote tool returns a budget estimate from your drawing and our team confirms the real figure within one business day.