Case Study: ISO Tank Container Rotary Jet Retrofit for Product-Switch Cleaning
A tank container depot retrofitted rotary jet heads for product-switch cleaning, cutting fresh water per unit 60 percent and cycle time 75 percent.
A tank container that returns from a wash with product heel still on its shell does not stay in service long. The next cargo picks up the residue, and the consignor rejects the unit. The depot then pays for a second cycle of 24 minutes and 1.8 cubic metres of fresh water that it never billed.
This case follows a tank container depot that retrofitted rotary jet heads in an enclosed wash bay for product-switch cleaning. The vessels are 20 ft frame tank containers carrying 17,500 to 26,000 litres. Every figure is the generic shape of this class of iso tank cleaning equipment, checked against published bands rather than a plant record.
Case Snapshot
The figures below are the generic shape of this class of retrofit, not a client record.
- Depot duty: 30 to 40 tank containers per bay-day on a 16 hour bay.
- Vessel class: 20 ft frame tank containers, 17,500 to 26,000 litres, representative 24,000 litres.
- Before: manual lance wash, 96 minutes and 4.5 cubic metres of fresh water per unit.
- After: two rotary jet heads at 120 L/min each and 6 bar, with a three-stage counterflow rinse.
A single 24,000 litre vessel presents tens of square metres of wetted steel plus two end heads. Every sizing number in this case hangs off that surface and the bay-day the depot has to hit.
The Challenge
A tank container is a stainless vessel inside an insulated steel frame. It has a top manhole, at least one top valve, and one bottom valve. Cargo moves in and out through hoses at those valves, usually with a pump.
The global fleet reached 848,400 units on 1 January 2024 (ITCO estimate). Each unit switches between cargoes many times a year, and each switch is a cleaning job. Any iso tank cleaning equipment decision at the depot starts with the cargo class, because the residue sets the wash chemistry.
Cargo classes follow the UN portable tank scheme. T11 covers wine and light liquids, and T4 covers non-hazardous oils. T14 covers hazardous chemicals and acids such as hydrochloric acid and zinc chloride. T50 covers LPG and ammonia. Hazard cargo follows IMDG, ADR/RID, and US DOT rules.
Acid-based chemicals run in rubber-lined shells, and the lining changes the wash. A hot caustic dose that suits stainless will attack the lining. The bay sets its wash chemistry to the shell type before it sets the heads.
Before the retrofit, the depot cleaned every unit with a hand lance. Two operators worked a hot water wand inside an open manway. Deep work meant a person entered the vessel to break residue off the floor and the end heads.
The hand lance failed on coverage, impact, and exposure at the same time. A lance is a point device, and an operator has to remember where the jet has been and how long it stayed. On a 24,000 litre vessel no pair of hands covers the interior evenly in one pass.
Impact falls with distance. Reach for the far end head and the jet arrives weak and dispersed. Move close and coverage collapses to a single patch. The measured residue stayed where the low impact coverage could not strip it.
Entry is the failure that ends the argument. Every deep clean meant a person inside a tank that had just held acid or oil residue. No amount of training makes that atmosphere benign.
The depot tried a fixed spray ball before it moved to rotary heads. A ball floods the shell and wets the whole wall at once. It leaves the end heads and every weld band behind a fitting only lightly touched. On a 24,000 litre vessel that shortfall showed up as a failed rinse.
The cost showed up in the daily ledger. The manual routine ran 96 minutes per unit, most of it waiting for heat and dwell. Fresh water ran 4.5 cubic metres per unit on a single pass with no recovery. Roughly 30 percent of units failed the initial rinse check and went back through the bay.
Soil Classes in Product-Switch Service
Product switching is the core problem, and the residues do not share one behaviour. A wine film rinses off with warm water in minutes. An oil film needs heat and a surfactant dose before the jet lands. An acid residue needs a neutralise step before the rinse, because a jet alone spreads it instead of removing it. The bay sets each wash from the class, not from a single house recipe.
| Residue family | Typical cargo class | Where it settles | What removes it |
|---|---|---|---|
| Wine, beer, and light liquid film | T11 | Lower shell and floor | Warm rinse, short dwell |
| Non-hazardous oil and vegetable oil | T4 | Mid wall and end heads | Hot wash with a surfactant dose |
| Acid and chemical residue | T14, rubber-lined shell | End heads and weld bands | Neutralise, then high-impact rinse |
| LPG and ammonia heel | T50 | Full shell after purge | Purge, then wet wash |
The shell material decides the chemistry. Rubber-lined shells serve acid-based chemicals, and a caustic dose that cleans stainless will degrade the lining. The bay reads the class from the unit paperwork and sets the wash before the heads fire.
The shadow map is common to every class. Every nozzle boss, brace, and valve throat on the inside of a tank container hides a band of residue behind it. A static device floods those zones and leaves them. A device that concentrates impact and returns to the same band does not.
The Enclosed Wash Bay
A depot yard is an open space, so rain, dust, and wind all reach a wash in progress. An enclosed bay removes that variable. The retrofit enclosed the pad, added an overhead gantry, and fixed the heads above the vessel.
The bay holds the vessel, the heads, the sump, and the recovery loop under one roof. Air handling keeps the working space clear, and the sump captures every litre that leaves the shell. Nothing runs to the yard drain.
Two rotary jet heads mount on the gantry. Each head turns on the cleaning liquid itself, so no motor or wiring enters the vessel. That matters for hazardous cargo, because a fluid-driven head carries no ignition source into the tank.
The bay runs one unit at a time on a fixed sequence. The vessel rolls in, the heads drop into the manways, and the cycle runs from a panel. One attendant manages the load, the sequence, and the rinse check.
The bay also fixes the drain path. Wash water leaves the shell into a sump on the low side, and the sump feeds the recovery loop rather than the yard. A sloped floor and a curb keep the pad dry between cycles. That detail matters at a depot that runs 30 to 40 units a day, because a wet pad slows every turn.
The Solution
Two rotary jet heads replaced the hand lance. Each head is fluid-driven: the cleaning liquid turns it through a repeating two-axis pattern while the jets scrub. The jets return to the same band many times inside one dwell window instead of wetting it once.
The heads were sized from published bands. The working flow window for this class is 10 to 150 L/min at 3 to 15 bar. Two heads at 120 L/min each sit inside that band, and the pattern repeats on a fixed cycle.
Rotary heads were chosen over static devices because the duty is impact, not flooding. A rotating spray ball runs at 2 to 5 bar and 10 to 60 L/min. It spreads wetting over 1.5 to 3 m of radius but adds almost no impact. A rotary jet takes over where the soil needs scrubbing, typically from 3 m diameter upward.
The rinse loop closed with counterflow. Instead of running fresh water once through, the bay runs three counterflow stages. The cleanest water meets the vessel last, and each stage overflows into the dirtier stage before it. Fresh makeup enters at the final stage only.
The cycle runs from a panel on a fixed sequence. Pre-rinse, hot wash, counterflow rinse, and drain follow in order, so two units never share a wash by accident. Rotary heads are the tank washing nozzles that carry the impact here. What depots call tank washin heads are the same devices in everyday speech. The attendant loads the vessel, checks the class, and starts the cycle.
Where a lighter duty is enough, the bay uses a spiral nozzle in the pre-rinse header and a flat-fan pair on the hatch throat. The full tank cleaning product range covers the wet end of the bay. The head selection logic follows published practice for rotary jet head tank cleaning, and the vessel class context sits with tank and vessel cleaning applications. The full method for this vessel class is set out in our guide to iso tank cleaning.
The Engineering
Five pieces of arithmetic carried the design. Each one is checkable with a flow meter, a pressure gauge, and a temperature probe.
Head duty and hydraulic power. Power at a jet is flow times pressure. With flow in litres per minute and pressure in bar, the working form is kW = Q times P divided by 612.
A single head at 120 L/min and 6 bar gives 120 times 6 divided by 612 = 720 / 612 = 1.18 kW. Two heads running together draw 240 times 6 divided by 612 = 1,440 / 612 = 2.35 kW at the nozzles. That is the pump duty behind the filtration, and it sets the motor size once pump efficiency is applied. The orifice equation behind these figures is worked in the nozzle flow rate calculation guide.
Pattern time and cycle. Pattern time runs 30 to 60 seconds per metre of the cleaning dimension. For a horizontal vessel the governing dimension is the shell length, about 5.3 m. At 45 s per metre that is 5.3 times 45 = 238 seconds, about 4 minutes of pattern time.
Add 20 percent for the two end heads: 4.0 times 1.2 = 4.8 minutes. The wash phase runs at about twice the pattern time to fold in chemical dwell: 2 times 4.8 = 9.6, about 10 minutes. With a 4 minute pre-rinse, a 10 minute wash, an 8 minute rinse, and a 2 minute drain, the cycle sums to 24 minutes. The phase total is 4 + 10 + 8 + 2 = 24.
Volume turnover check. One relation cross-checks the cycle. Turnovers follow N = Q times t divided by V, where Q is flow, t is time, and V is vessel volume in litres.
A single turnover of 24,000 litres at a combined 240 L/min would take 24,000 / 240 = 100 minutes. A 10 minute wet clock is 0.1 of a turnover. That gap is the point: jet cleaning works on repeated impact, not on displacing the vessel volume.
Orifice wear. Orifices grow with abrasion, and flow rises with the square of diameter at constant pressure. A diameter growth of x percent raises flow by about (1 + x/100) squared minus 1.
At 10 percent growth, (1.10) squared minus 1 = 1.21 minus 1 = 0.21, so 21 percent more water. The pump then moves 240 times 1.21 = 290.4 L/min. Hydraulic power climbs from 2.35 to 2.35 times 1.21 = 2.84 kW.
The bay uses an 8 to 10 percent diameter growth band as its rebuild trigger. A rise in head flow at constant pressure shows the wear before the pattern fails. The high pressure orifice selection guide covers those bands.
The pump set is sized on the two heads together, not on one. A 240 L/min duty at 6 bar is the 2.35 kW of jet power computed above. The motor is chosen above that figure once pump efficiency is applied. A duplex strainer at 100 to 200 microns sits upstream of the heads. Differential pressure gauges and a changeover valve let the attendant clean one basket while the other keeps the bay running.
Counterflow Rinse and Water Reuse
Counterflow reuse set the water figure. The bay runs three counterflow stages, each applying 1.5 cubic metres of rinse liquor per unit. Run once through, that is 3 times 1.5 = 4.5 cubic metres.
With recovery reclaiming about 80 percent of each stage overflow into the stage before it, fresh makeup falls to the final stage. That is 1.5 cubic metres plus about 0.3 cubic metres of blowdown and losses, or 1.8 cubic metres per unit. The cut on the rinse is (4.5 minus 1.8) / 4.5 = 2.7 / 4.5 = 60 percent. At 30 units a day the daily draw falls from 30 times 4.5 = 135 cubic metres to 30 times 1.8 = 54 cubic metres. The saving lands on both fresh water and the heat that fresh water once carried.
Heating load. The hot loop holds 60 C, and makeup returns at 10 C from mains. With flow in litres per hour and a lift in degrees Celsius, the working form is kW = flow times delta T divided by 860.
At a metered makeup of 3,375 L/h and a lift of 50 C, the load is 196.2 kW. The form is 3,375 times 50 / 860 = 168,750 / 860 = 196.2. Read it the other way and the daily figure ties: 30 units at 1.8 cubic metres each is 54 cubic metres of makeup, and 54,000 litres spread over the 16 hour bay is exactly the 3,375 L/h the meter shows. The heater is the largest single energy load in the bay. It sits well above the 2.35 kW of jet power, which is why the recovery loop pays in heat as much as in water.
Warm water does more than carry heat. Water at 60 C has roughly half the viscosity of water at 10 C. A warm jet therefore cuts and spreads through a draining film differently. That is why the hot step runs ahead of the final rinse, not instead of it.
The Results
No plant audit figures appear below. These are working outcomes for this class of retrofit, built from the arithmetic above and kept inside published bands.
| Metric per unit | Before (manual lance) | After (rotary jet) | Basis |
|---|---|---|---|
| Cycle minutes | 96 | 24 | Phase sum |
| Fresh water per unit | 4.5 cubic metres | 1.8 cubic metres | Once-through versus counterflow makeup |
| Fresh water at 30 units a day | 135 cubic metres | 54 cubic metres | 30 times the per-unit figure |
| Units per bay-day | 10 | 40 | 960 minute bay-day divided by cycle |
| Labor per unit | 3.2 worker-hours | 0.4 worker-hour | Two operators versus one attendant |
| Entry events per unit | 1 | 0 | No manual entry in the new cycle |
| Initial-pass rinse failures | 30 percent | 6 percent | Rinse check |
The rinse failure rate deserves the last word, because it multiplies everything else. A failed unit re-enters the bay for a second 24 minute cycle and a second draw of fresh water. At 30 units a bay-day, moving from a 30 percent to a 6 percent failure rate removes about seven rewash cycles a day. Not one extra litre is spent on the working pass to buy that gain.
Reading the Numbers Against Published Ranges
Every sizing figure sits inside a band published for this equipment class.
Head flow of 120 L/min per head sits inside the 10 to 150 L/min window at 3 to 15 bar. The 3 m class boundary applies here. This vessel is 2.4 m in diameter, so two heads cover it well. The valve bosses still shadow small bands, and the second head reaches them.
Pattern time of 45 seconds per metre sits inside the 30 to 60 second band. A cycle of 24 minutes sits inside the published 15 to 30 minute budget for a 3 to 6 m tank, including rinse and drain.
The counterflow cut of 60 percent sits beside the closest published precedent, an oilfield wash bay that moved fresh water from 4.5 to 1.5 cubic metres per vessel, a 67 percent cut. The figure here lands below that precedent because its final-stage blowdown is larger. The heating load of 196.2 kW is a working figure for the metered makeup, not a plant record.
One boundary is geometric. Above about 13.7 m diameter a single fluid-driven head runs out of reach, and machine-class units with independent drives take over. This vessel sits far below that line, so a fluid-driven head is the right class.
The recovery figure is the one most sensitive to service discipline. A clogged strainer or a lazy blowdown both push fresh makeup back up. The bay meters makeup per unit and logs it, so the counterflow gain is visible on a daily sheet rather than assumed.
Verification and Quality Checks
Verification is a rinse check, not an opinion. The bay runs a conductivity or visual check on the final rinse and releases the unit only when it clears. A failed check sends the unit back through a full cycle.
Hazard classes add steps. A T14 acid unit needs the neutralise step logged before the wash begins. A T50 unit needs a documented purge before any wet work. Hazard cargo follows IMDG, ADR/RID, and US DOT rules, and the depot files the wash record with the unit.
Nozzle identity and flow are checked against published standards. ISO 10625 tip colour coding gives the bay a common language for tip identification. ANSI/ASAE S386 sets the flow tolerance a replacement tip must hold.
The record matters as much as the wash. A unit that passes with a logged cycle and a logged rinse check leaves the depot with evidence, and evidence keeps a unit moving.
Why This Matters
The transferable asset is the method, not the hardware list. A wash bay for tank containers runs on the same five numbers. They are head flow at pressure, pattern time against the cleaning dimension, and the recovery split. The heating load and the wear band that triggers a rebuild complete the set. Any iso tank cleaning equipment study that skips one of the five will surprise somebody during commissioning.
A rotary head concentrates and repeats, while a static device floods and leaves shadows. A railcar wash boom retrofit ran the same shadow logic on tank car exteriors. A conveyor belt spray wash retrofit shows the same recovery discipline on a moving line.
A retained hand lance still has a place for a hatch throat or an awkward weld band. It should finish a unit the heads have mostly cleaned, not carry the job.
The method scales across vessel classes. A small tank wash nozzle on the pre-rinse header and a rotating tank washing nozzle on the final rinse both sit inside the same sequence. That sequence is vent, heat, impact, recover, and verify.
Tank container cleaning at a depot is schedule-driven, so the method has to survive a busy day. A tank washing system built on that fixed order behaves predictably. A bay that behaves predictably is a bay you can staff, permit, and audit.
The same five numbers size a single bay or a fleet depot. Head flow picks the pump, pattern time picks the cycle, and the recovery split picks the tank farm. The wear band picks the maintenance calendar. Get those right and the retrofit is a wiring job, not a rebuild. Tank washing equipment chosen on that basis holds its duty across a whole fleet.
The decision checklist that came out of this bay is short enough to laminate.
- Vent and hold before wash; keep people out of the vessel.
- Size head flow at pressure from the published band, not from a nameplate.
- Set pattern time against the cleaning dimension, with heat ahead of impact.
- Close the rinse loop with counterflow and meter fresh makeup per unit.
- Rebuild heads on a wear band measured as flow rise at constant pressure.
- Verify every unit with a rinse check before it leaves the bay.
The Final Call
BoreJet supplies nozzles and does the sizing arithmetic behind them for this class of iso tank cleaning equipment. That covers head flow at pressure, pattern time, the recovery split, and the heating load.
Send the vessel volume, the residue class, and the metered water figure through the contact page. The response comes back with head count, orifice sizes, and a rinse sequence that fits your throughput.
Your Duty May Differ
Send the Vessel Drawing and the Pump Curve.
We size the head class, the count and the operating point for your tank, not a catalogue guess. A coverage test on the actual vessel beats any estimate.