Stainless  Restora‚Äčtion Ltd

Metal Finishing and Surface Engineering Technologies

SRL Technical Library

PICKLING AND PASSIVATION TROUBLESHOOTING  During, following or indeed before the cleaning operation all sorts of strange things can occur as a result of the chemicals used. Our technical library gives a variety of examples that SRL has encountered along its way. This list is by no means complete - these pages will be continually updated as we/you experience other strange phenomena.

Over Pickling

Identification

This can manifest itself in a number of ways from slight over pickling to severe over pickling such as that shown in the picture.  "Frosting" of the welds is one sign of over pickling. This is often seen in TIG weld deposits. MMA, MIG and FCW weld deposits are not so sensitive to frosting. 

Over pickling is difficult to achieve when using manual pickle paste which is brushed onto the weld zone since a thin film is applied and once that acid film is spent then the pickling process slows and eventually stops. In the case of immersion pickling then it is a different matter since fresh acid is continually washed against the surface and therefore pickling (corrosion) is rapid.

It is important to note that a dirty bath i.e. one laden with high Fe (iron) deposits will have a detrimental effect on the stainless steel surface and increase the risk of isolated accelerated corrosion attack and over pickling.

Possible Detriment

Apart from the fact that the surface will look unsightly and indeed, if a food/pharmaceutical bearing surface it will look unhygienic.  It is obvious that once a weld has  decayed then the mechanical properties of that weld may have been compromised and lead to design failure.

Solution

If the welds have completely dissolved away as those in the picture then needless to say you will have to cut and repair.

If the general (whole) surface of the steel has become over pickled then the only remedy is to mechanically polish the offending pits and crevices out and to "bottom" out the steel to a sound base once again, free from crevices/pits/voids/etc, which will give rise to corrosion attack.

Method: It is difficult to over pickle a surface, but if you wish to take the safe option a manual pickling operation such as brush application or indeed spray gel application can be used.

Products  Available

Pickling Products

Cleaning Products

Technical Notes

It is important to follow the instruction given for each individual product used and the advice given in the "product application data sheets" available on line in the product section of SRL Chemical and Analytical Services Ltd.

Information given in this page may be subject to alteration without notice.

Care has been taken to ensure that the contents of this publication are accurate but SRL Site Services Ltd do not accept responsibility for errors or for information that is found to be misleading.

Suggestions for, or descriptions of, the end use or application of products or methods of working are for information only and the company accept no liability in respect thereof.

Before using products supplied or manufactured by the company the customer should be satisfied of their suitability.

If further assistance is required, we have access to extensive research facilities, we will often be willing to help.

Stainless Restoration Ltd, Adamsons Industrial Estate, Hyde SK14 1EE

Stainless Restoration Ltd offer an Electropolishing service to the stainless steel fabrication/manufacturing industry at its newly refurbished fully automated Electropolishing plant at Hyde Manchester.