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Pickling & Passivation, start-up of a pickling bath

{ 12 februari, 2020 }

This procedure describes the start-up of a pickling bath for stainless steel parts.  For this set-up an initial order was placed of 2000 Ltrs. Pickling Batch Concentrate.

Start-up of the bath


a bath was used with a content of 400 Ltrs.  The bath was filled as follows :

  • 200 Ltrs tap water
  • 200 Ltrs Pickling Bath Concentrate

Temperature of the bath :

  • After filling the bath : Temp of 23°C
  • After 1hour : Temp of 20°C
  • After 12hrs : Temp of 17°C
  • After 36hrs : Temp of 13°C

Pickling Time of Stainless Steel 304 & 316 is between 60 and 90 minutes at room temperature of around 20°C.

Per 10°C less the pickling time will double up
Per 10°C more the pickling time will be half

For this reason it is important to monitor the temperature of the bath on a regular base.

Next to the improvised Pickling bath also a small rinsing bath was improvised.  This rinsing bath is to have a first simple rinsing once the parts come out of the pickling bath.

At start the rinsing bath, filled with normal tap water, has a neutral pH (7) as normal tap water is used.

The parts contain residue of the Pickling product and the pH will decrease.

Once a pH of 3,5 to 3 is reached, it is recommended to renew the rinsing bath with fresh tap water

Submerging the parts


The parts need to be completely clean before they can go in the bath.  “Hang” the parts in the bath using cords.  It is important that the pieces don’t touch the bottom of the bath or each other.

The parts have to be in the bath min. 60 to 90 minutes at a temperature of around 20°C.

The parts already have a very nice surface after rinsing in the bath.
However on the weld we can clearly see the black remaining.

This is iron that came to the surface due to the pickling product but which is still ‘stitched’ to the surface pretty hard.

Rinsing with high pressure


After the rinsing in the bath it is very important to rinse thoroughly with high pressure (min. 150 bar).

There are 2 reasons:

  • To rinse/neutralize the acidity completely of the pickling bath
  • To remove all remaining iron from the surface




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