All the models in the range use a high carbon steel body as standard, and when required the complete machine can be custom built in 304 stainless steel. This difference lies in corrosion resistance and nowhere else. Explaining it clearly is more useful than adding one more line of material data to a quotation, because much of the corrosion judgement made on site is in fact an environmental judgement that has gone wrong.
What the two steels do in the environment
High carbon steel is adequate in an ordinary indoor environment and the surface condition stays stable over time. The problem appears in damp, salt spray or corrosive environments: corrosion starts at the weak points of the paint film, gradually blisters and flakes, and once the corrosion products are carried into the interior of the machine with the oil flow they bring new difficulties to the filtration section and the valves. In such an environment, building the complete machine in 304 stainless steel holds the surface condition noticeably better, and that is where its real value lies.
Coastal high salt spray, work areas that are washed down regularly, and places where corrosive media are stored are situations where it is worth working the numbers out properly. When the machine runs continuously for long periods rather than being used occasionally, the difference in material is magnified by time, and the custom build only looks worthwhile once it is spread over years of operation.
The other side has to be counted as well: indoors, dry, with an oil that carries no corrosive constituents of its own, and with a machine that does not run all year, high carbon steel performs steadily, and the price difference that the custom build brings does not buy a corresponding extension of service life. In such cases it is more sensible to spend the budget elsewhere, for example on a spare set of filter elements or on complete measuring equipment.
The material solves the corrosion question and nothing else
This has to be said clearly: changing to 304 does not make the filtration accuracy higher and does not make the degassing more complete. The filtration accuracy of ≤1 μm is determined by the element specification and the number of filtration stages, the water content of ≤3 ppm depends on the working condition of the vacuum system and on the level of temperature control, and the breakdown voltage of ≥65 kV and NAS 1638 class 5 depend on the oil itself and on the treatment process. These indicators have nothing to do with the steel the body is made of.
Using the material to solve a question of performance gets the direction wrong. To improve the degassing what has to be changed is the working condition of the vacuum system, the temperature range and the pretreatment of the oil; to improve the cleanliness what has to be changed is the number of filtration stages and the accuracy of the elements. Confirming these two kinds of objective separately from the material selection is what keeps three things from being run together at acceptance.
Three things to confirm before deciding
| Condition of use | How high carbon steel behaves | What 304 stainless steel changes | What still has to be confirmed separately |
|---|---|---|---|
| Dry, ventilated indoor | The surface condition stays stable | Equally stable | Whether the cost of the custom build is necessary |
| Coastal, high salt spray | Corrosion gradually appears | The surface condition is held better | The protection of the electrical parts is checked separately |
| Damp, washed down regularly | Corrosion develops faster | Behaves better | The drainage and sealing conditions |
| The oil itself contains water and salt | The tank and pipework are affected | Greater corrosion resistance | The filtration and degassing figures do not change because of it |
Confirm the whole machine conditions before custom building
- First establish whether the corrosion comes from the environment or from the oil, because the measures differ
- A material upgrade changes none of the processing indicators; the indicators are checked separately
- When custom building, confirm the dimensions, the weight and the connection form at the same time
- The protection rating of the electrical cabinet is checked separately and does not rise automatically with the body material
304 answers whether the equipment will corrode, not how well it processes the oil; confirming the two separately is what keeps one investment from being expected to deliver the other result, and what keeps the account from being muddled at acceptance.