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.

Insufficient Water Rinse

Pickling Insufficient Water Rinse

Identification - Tea Staining

This is a very common problem and is attributed to insufficient rinse down of the surface following a pickling operation.It is important to note that the powerful etching process at work during pickling can only be described as an accelerated corrosion process. Uniform levels of stock is dissolved (etched) from the surface during the contact time. As a result large amounts of metal salts are released into the chemical pickling solution and will be removed during wash down, however, a large amount of salts will be deposited on the surfaces as Cr, Ni, and Fe salts other by products will be present depending on the steel grade and the make - up of the acid, Fluoride salts will be present also.You can imaging that a typical 300 series (316L) grade of steel has an analysis of 17%Cr - 12%Ni - 3%Mo and Fe balance. From this information we can see that the biggest element (salt) to be produced will be iron (Fe), somewhere in the order of 70% of the metals being pulled of the surface will be iron. If this by product is not rinsed from the surface properly then brown rusting (iron oxide) will occur within days or even hours. This staining is also known as "tea" staining.

Possible Detriment

 Apart from the fact that the surface will look unsightly and indeed, if a food/pharmaceutical bearing surface it will look unhygienic.The product will detach itself from the surface very easily and will readily contaminate any product that will pass over its surface; therefore it must be removed before the fabrication enters into service.The surface of the steel is also contaminated and will not form a passive film therefore is susceptible to corrosion attack

Solution

This product is only lightly adhered to the surface and can be removed with a quality cleaner such as the Enerjex 410 The area needs to be HP washed down with plenty of clean water to remove all product. A re-pickle is not required.

Method: Cover the entire fabrication with Enerjex 410 listed in the product section. If the fabrication is large and the offending area to clean is small then the area can be wiped down with Enerjex 410. Once the offending chemical stain is removed the area needs to be HP washed or wiped down with Enerjex 610 and then clean water.

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.