Stainless  Restora​tion 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.

Smut Staining

Identification

Appears as a grey or brown mottled stain across the surface, more often on cold rolled sheet stainless steel. Can be across a whole surface or in isolated patches.

Possible Detriment

The surface will look stained. There is evidence that these regions are lower in corrosion resistance that the remainder of the surface.

Solution

This phenomena is more common in sensitive steels surfaces such as those of cold rolled type. The cause is a build-up of iron (Fe² ions) at the acid/metal interface. The pickling process dissolves iron from the surface and if allowed to remain close to the surface can build-up to a level where it is not oxidised to Fe3 ions which are necessary in the formation of the passive film.

If the Fe² ions are allowed to remain and not oxidised to Fe3 ions they will appear as dark areas "under" the surface.Another way of reducing the level of smutting is to conduct a slower pickle over a longer time with a weaker solution. Avesta 215 spray pickle gel is ideal for such occasions.

Method: This problem can occur whether immersion bath pickling or Spray gel pickling.

Note: in immersion bath situations it is advisable to agitate the solution to wash the Fe² iron away, and in the case of a manual pickling operation with spray gel (Avesta 204 or 215 for example) it is sometimes possible to see the suspect areas as dark brown areas in this case it is advisable to spray the suspected areas, and indeed the whole surface if possible, with Desmut 5 - See product section

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.