Cyclic Condensation Test Chamber Configuration Per DIN 50018

A test for sulphurous damp

DIN 50018 is a German corrosion standard, known widely as the Kesternich test after the man who shaped it.

It checks how a coated or plated part holds up when condensation forms on it carrying dissolved sulphur dioxide, the acid that hangs in industrial air and city rain.

What the Kesternich name carries

The test was built to copy a real climate: the sulphurous, damp air of industrial regions, where coal smoke and exhaust put sulphur dioxide into the sky and rain brings it down as a weak acid. For a car that means the parts under the body, the brackets and clips and plated fasteners that meet road spray, winter salt, and the sulphur in traffic fumes year after year. The standard reaches back to the decades when sulphur dioxide was the signature pollutant of factory towns, and it still stands in for any place where fuel is burned and the air turns sour.

DIN 50018 packs that slow attack into a few days by making acidic dew form on the part again and again, so a coating that would take winters to fail in the field can be sorted from a sound one inside a working week.

The eight-and-sixteen-hour cycle

A Kesternich cycle runs in two halves across a day. For the first eight hours the chamber holds the air warm and at full saturation with a measured charge of sulphur dioxide sealed inside, and condensation forms on the part, a film of water that takes up the gas and turns into a weak sulphurous acid against the metal. For the next sixteen hours the chamber opens to ventilate, the gas clears, and the part dries in moving air.

That rest half is as much the test as the wet one, since the drying lets oxygen reach the wetted metal and lets the corrosion set before the next charge of acid arrives. A run is counted in these whole cycles, two or five or ten of them, and each one wets the part, lets the acid bite, then dries it and starts again. The damage builds from the swing between acid dew and open air, so a chamber that skips the clean dry phase or never quite saturates in the wet one gives a softer test than the standard means it to be.

Why a car part meets this

DIN 50018 judges the finish on a part rather than the silicon sealed inside it. It works on the outside of an assembled piece: the plating on a fastener, the coating on a bracket, the finish on a connector shell, the surfaces a car exposes to dirty, damp air.

Dosing the sulphur dioxide

The heart of the chamber is the gas charge, and the standard fixes it not as a concentration to chase but as a measured volume of sulphur dioxide poured into a chamber of known size. The common doses are two tenths of a litre, one litre, or two litres of gas for every three hundred litres of chamber space, and the more gas the charge carries the harsher the grade it earns. The gas does almost nothing on its own. The work begins only when it dissolves into the condensation forming on the part and turns that film into a weak sulphurous acid against the metal, so the whole severity of the test rides on how much gas ends up in the water on the surface. That makes the dosing the hard part of the build. Too little gas gives a mild acid that flatters a weak coating into passing; too much pushes the attack past anything the part would ever meet on a road. The chamber has to seal tight enough that the charge does not leak away over the eight wet hours, spread the gas evenly so a part at one end of the rack meets the same acid as a part at the other, and meter the volume it admits closely enough that one run can be compared against the next, since a dose read loosely turns a graded corrosion test into a rough guess no two labs can agree on.

Condensing the acid onto the part

As in any condensation test, the water has to form on the part and not on the walls. The chamber warms its walls and floods the air to saturation, and the part, sitting a touch cooler, draws the dew onto itself. What differs here is what the dew becomes: as it forms it takes up the sulphur dioxide around it and turns acidic on the metal, so the part is washed in a weak acid for the whole wet half of the cycle.

A film that builds and clings is what does the damage; one that sheets off and drips away carries the acid down the drain before it can bite, so the chamber holds the saturation steady and the part only a touch below the dew point to keep the wetting slow.

The warmth that drives the dew

DIN 50018 runs warm rather than hot, holding the wet phase around forty degrees with water standing in the base of the chamber to keep the air at saturation. That gentle warmth matters: it is enough to drive a steady film of condensation and to speed the chemistry of the acid on the metal, while staying close to the temperatures a parked car meets on a humid day.

The chamber heats the water and the walls together, watches the air stay saturated, and leaves the load just cool enough that the dew gathers on the parts and not on the lining.

Lining a box that meets acid

A box that makes acidic dew will corrode itself unless it is built to resist. The inner walls, the rack, the door seal, and the plumbing meet warm sulphurous acid every cycle, so the chamber is lined with glass, with acid-stable plastics, or with coatings chosen to shrug off the attack, and the heater and sensors are shielded or made of materials the acid leaves alone.

A chamber that rusts on the inside both fails early and seeds the test with its own corrosion products, which can settle on the parts and skew the grade, so keeping the box inert is part of keeping the test honest.

Handling the gas safely

Sulphur dioxide is sharp and harmful to breathe, so the chamber stays gas-tight through the wet phase and vents through a scrubber that neutralises the gas before it reaches the room. The sixteen-hour ventilation phase clears the chamber the same way, into the wash and not into the lab.

Holding it even across a loaded rack

A corrosion run rarely holds one part. A rack of fasteners, brackets, and coated coupons fills the chamber, and the grade is fair only if every piece sees the same acid. The chamber has to keep its temperature and saturation uniform so a part at the edge wets like one in the middle, and it has to spread the gas so no corner runs lean. A piece in a warm pocket never quite reaches the dew point, escapes the acid the others get, and comes out looking better than its coating deserves.

Where the acid bites

Acidic dew finds the weak places in a finish. On electroplated steel it eats through a thin or porous layer of zinc or nickel and rusts the base metal under it, raising the red bloom the test grades against. On a painted or powder-coated bracket it creeps under a scratch or a cut edge, lifts the coating into a blister, and undercuts it from the flaw outward.

At a plated contact it corrodes the surface and climbs the resistance until the joint reads high and the signal through it falters. In a seam it draws in by capillary action and holds the acid long after the face has dried, so the corrosion runs on out of sight.

What a soft run hides

A part passed on a chamber that under-dosed the gas or never quite made the dew form does not fail on the bench. It fails as a rusted fastener or a blistered bracket a couple of winters into service, when the road has done what the weak test did not.

Reading the part after the cycles

After the run the part is judged against the standard's scale. The surface is graded for corrosion and rust, a coating is checked for blisters and for how far the attack has crept from a scribe cut, and a plated layer can be measured for loss or sectioned to show how deep the acid reached. The judging is done by eye against reference photographs and by simple measurement, and two labs that ran the same grade should land on the same verdict for the same part.

A part that comes through within the grade earns its pass; one that has rusted or blistered past the limit goes back for a thicker plating, a tougher coating, or a sealed edge before it is run again.

Where it sits among the climate tests

DIN 50018 is one test in a wider corrosion programme, run beside neutral salt spray, cyclic corrosion tests, and the plain cyclic condensation of standards like VDA 230-208. Salt spray attacks with chloride, plain condensation with clean dew, and the Kesternich test with sulphurous acid, and each finds a failure the others miss. A part bound for a car runs several of them, and the SO2 condensation chamber carries the share that copies the acid in dirty air, the slow sulphurous bite that belongs to industrial weather alone.

The box that breathes acid

Other climate chambers work to keep the air clean and the water pure; this one works to foul both on purpose, to charge the dew with acid and pour it onto the part on a clock. DIN 50018 trusts a chamber that can dose the gas by the litre, condense it where it bites, dry the part between rounds, and resist the acid through all of it.

Get the configuration right and the part that comes out within grade is one that will hold its finish through years of sulphurous, salted, rainy roads, while a chamber that doses light or condenses poorly hands out a pass that the first hard winter takes back as rust blooming along an edge the test never wet.