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Steel De-scaling

Steel de-scaling removes scale buildup on mild and hot rolled steel

Steel de-scaling is accomplished by two different applications. If the purpose is to remove process-scale on a steel coil, for instance, an immersion system is the usual approach. The second application is steel de-scaling a mild steel washer. Normally, one uses the equipment of the washer to help descale it.

In the first application, immersion steel de-scaling is known as acid pickling. Vanchem Performance Chemicals’ product, VANCHEM RSH, can be used for acid pickling in an immersion system. Vanchem recommends a concentration of 15-25% v/v, at ambient temperature. The immersion time depends on the level of scale.

This application will de-scale both gas-metal-arc-welding (GMAW) and (MIG) welding flux from welded joints. Welded joints have been traditionally hard to paint because they need to be pickled beforehand. The parts in question must first be cleaned with an alkaline cleaner and rinsed, then pickled in VANCHEM RSH solution. The pickling removes weld flux debris, which is not removed in general alkaline cleaning.

The second application, steel de-scaling industrial washers, is utilized to remove built-up scale formed by hard water deposits, and other scales, including organic precipitates. The VANCHEM RSH contains an effective inhibitor providing maximum protection against acid attack. The procedure outlined below is general and can be used for any industrial washer.

Washer Steel De-scaling Procedure:

  • Drain and flush stage. Remove all sludge, soil, fallen parts etc., before filling with water.

  • If the walls of the washer have large amounts of scale built-up, aim nozzles directly at wall to remove scale.

  • Turn washer exhaust fans on, and leave on for the entire operation.

  • Fill tank ½ to ¾ full with city water. Add enough VANCHEM RSH to give a 10-30% solution depending on the amount of scale. Concentrations less than 10% v/v will require longer circulation times, and may not remove all the scale present.

  • Caution should be exercised when pumping RSH from the drum into the tank. Secure discharge hose with wire or tie wraps. You will require an acid resistant pump when transferring RSH.

  • All bag filters should be removed from canisters, if applicable.

  • Add heat to at least the operating temperature. At higher temperatures, less foam and faster cleaning times will result.

  • With lower concentrations and lower temperatures, foam may occur. Use our DEFOAMER 18 when this occurs.

  • Because of the corrosive nature of the VANCHEM RSH fumes, be sure to isolate the stage with plastic tarps or poly-wrap. This can be done by covering the entrance and exit doorways of the stage.

  • Another way to achieve the same effect if the stage is in the middle of the washer is fill adjacent tanks with water and circulate water to act as a water curtain. The water will scrub acid fumes from the air and prevent fumes from escaping into the plant. The water in the adjacent tanks will likely need to be neutralized once the steel de-scaling operation is completed.

  • Remove all metal parts and equipment stored in the area. Move to another location well away from the steel de-scaling operation.

  • We recommend that steel de-scaling be done during plant down times and not during production, the acid fumes may bother people working in the area.

  • Ventilate area well with fans, open windows, open doors, etc. We recommend that shipping doors and exit doors be opened to allow lots of fresh air into and out of the plant during steel de-scaling.

  • Circulate for 2-10 hours depending on amount of scale and cleanliness desired.

  • Evaluate inside of washer after 2 hours. Caution should be exercised to avoid skin contact with overhead drips…wear proper personal protection equipment.

  • Continue circulation and inspection until desired cleanliness is achieved.

  • Neutralize acid with caustic if required. Use the same safety precautions when pumping caustic. A rough rule of thumb to follow; a third to a half drum of 50% sodium hydroxide (caustic) for every drum of RSH. The exact amount of caustic will depend on the amount of dissolved scale in the acid solution.

  • Pump out neutralized acid. Fill with city water and circulate, neutralize as required. When the pH of the water matches that of the incoming city water, dump and refill again. Be sure to have a high-pressure hose available for washing down all the walls and tank.

  • Recharge with Vanchem production material and realign nozzles.

For more information, contact Vanchem at our corporate headquarters in Burlington Ontario.

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