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.

Pipe Weld Root Oxidation


This feature can and will occur in the underside (internal surface) of a pipe weld if the atmosphere in the pipe is not displaced and exchanged for an inert atmosphere such as that of Argon or Argon/Nitrogen mix. The "rainbow" coloured appearance of the oxidised surface of the root and HAZ is attributed to the exposure of the steel surface to temperatures above approx. 4000°C. When the stainless steel surface is raised to around this temperature it tends to oxidise (straw colour) in the atmosphere. The degree of oxidation, therefore the degree of colours, will depend on the steel thickness, temperature reached and to an extent the analysis of the material.

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 in the offending areas is damaged by the weld oxide and has a lower corrosion resistance than the remainder of the surface, this oxide damage will also inhibit the formation of a passive film therefore is further susceptible to corrosion attack.


These areas are often pipe but welds in long spools of pipe and of course are inaccessible, the only practical means of reaching and treating these areas is to circulate.

Method: The pipe spool needs to be connected so as to form a closed loop system so cleaners and pickling solutions can be circulated through its entire length. Care has to me made to avoid air pockets and ensure that all the internal pipe surface is contacted with the solutions.

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.