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Removal of "blueing" on SAF 2507 welds

We are processing SAF 2507 for a desalination plant and are experiencing difficulty in removal of the Blue arround the heat affected zone of the weld. So far we have used the standard system of passivation which is based on 3%hf and 10%nitric using a spray on wash off. This reduces the effect but we require to remove it due to potential corrosion issues when the sea water meets the heat effected zone. Any suggestions we would be interested to hear.

Mark Fuller
Fabricating shop manager - Newcastle, NSW, Australia
June 23, 2008

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First of two simultaneous responses -- June 24, 2008

Mark,

As you has noticed the blue is around the heated area of the weld, where you find some blue in color. It should be remaindered that the area not only appears in blue, but bears heat-induced stress as well. It is real that the corrosion resistance reduces is great contributed by stress. If you realized that fact, it is suggested you may line up as nnealing parts followed by welding, then chemical ¡°blue¡± removing followed passivating, in which the parts will have optimized corrosion resistance against sea water.

Jun Zhang
- Cincinnati ,Ohio

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Second of two simultaneous responses -- June 25, 2008

Hi Mark

You could look at electrolytic weld cleaners. They are used to remove heat scale and will passivate the stainless steel after welding . Much the same principle as electropolishing of stainless steel only this is done with a portable rectifier and a brush or wand which has been soaked in a recommended solution. If you do a search on the web you should find out more information about this.

I hope this is of help.

Regards,

Paul Inskip
Melbourne, Victoria, Australia

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July 1, 2008

There are three basic methods for removing the weld discoloration of the heat affected zone on stainless steel.

1) Mechanical removal, grinding or blasting, etc.
2) Pickling, usually a nitric-based paste product
3) The electrochemical method mentioned above by Paul Inskip

All three have advantages and disadvantages depending on the application and what equipment is available to you.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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Guys

Thanks for you answers.

We have tryed the electropolishing machines - unfortunately the main problem is the internal weld surface which the machine head's cannot reach.

So far our only solution is to totally immerse the pipe in 3-6%hf and 10-20%Nitric - we are fabricators not chemical handlers and the amount of acid required - 3000ltrs is scary - any other suggestions would be welcome.

Mark Fuller
- Newcastle, NSW, Australia
July 6, 2008