Stainless Steel Contamination

Perhaps you are experiencing Metal-Metal solution such as Material Scientists study.

Next time, may be you should follow the rule of healthy and healthful cooking: Always wash your knife after every use before using it to cut another edible.

It's not clear what exact is the problem, are you getting rust on ground surface or rusting at the point of weld?

What kind of welding are you doing?

What is the welding material?

Are you welding SS with some other material?

Are you doing grinding after welding?

Thanks for responding - we getting rust on the ground surface - someone made comment that the S/steel is contaminated by the carbon and mildsteel from grinding disc that cause the rust at the ground surfaces, grinding is needed to V the joint to be welded on 10 mm Stainless their is signs of rust next to weld but seen more on the grinding marks

You are referring to corrosion of SS equipment due to surface contamination by carbon steels during fabrication. Corrosion of SS at sites of iron contamination is all too common in fabrication shops processing both materials. One way to avoid iron contamination of SS is to have dedicated facilities for fabricating SS equipment. Brushes, grinding wheels, etc. should not be ferrous based. SS equipment can also be cleaned/passivated after fabrication with solutions designed to remove iron contamination.

Protection to stainless isprovided by having high hardness alloy mixed with low hardness phase. High hardness is chrome rich alloy and during grinding if it is not uniform the grind area will show the rust because of loss of high chrome phase in the matrix.

Hello, there is nothing worse than having stainless welds to start rusting. There could be several reasons this is occurring but these are the most common. I find it occurs more due to wire brushes than grinding disks but I have seen it from using a contaminated file to clean up the weld after complete as well. The rust is only on the surface and can be easily brushed of with a non contaminated wire brush. I have seen a rusting problem occur when stainless steel is stored in mild steel pipe racks too but this would not be just in welding areas. if you passivate the welds after completion this problem should go away on it's on.

1)If you buff the weld with a carbon brush. If you buff or grind the weld with a brush that has been used on carbon steel.

2)If you use a cheap wire brush that is not truly stainless steel through out. We had this happen one time and after investigating I found the wire in the brush was only plated with stainless steel. Most of the wire brushes I have seen are made from 302 type stainless wire for some reason which I assumed was cost.

3) If you use the improper welding electrode such as a 309 and the welder overheats the weld and HAZ when welding. With stainless steel welding it is all about color of the finished weld, if you are getting a dark grey or blackish color in the finished 309 electrode weld it could cause the weld to rust due to the extra ferrite content of th e electrode.

pipewelder

You mentioned welding induced rust as well. We deal alot with duplex stainless product and when we weld the stainless must be heat anealed to regain or retain its corrosion resistance. Although I am not a metalurgist I do know that stainless that reaches 1200 - 1800 Degrees Farenheit will lose some of its corosion resistance and should be taken to 2200 degrees for an hour and quenched. I beleive it has something to do with normalizing the nitrogen content of the surface material.

One rule we use around the shop is to keep the stainless and mild steel separated along with the tools that are used to work on it. I have seen this weld rusting problem hundreds of times in the 30 years I have fooled with pipe welding. It has nearly always been from some green helper or an idiot who just don't care buffing a weld with an improper wire brush.

Duplex stainless can be very tricky to weld correctly. One of the main things to watch when welding duplex is the inter-pass temperature. If you get it too hot then you will not have the ferrite and non ferrite combination needed to make the weld metal match the base metal metallurgy. One good thing about duplex is the fact that it can handle vibration like carbon steel and still have the anti corrosion capabilities of stainless. I have one digester that is made entirely from duplex and it is the "cats meow" of digester building material IMO.

pipewelder

My experience from stainless castings is that the iron from the grinding wheels is the problem We ground thousands of welds in most grades of stainless including duplex and had no problem. We used no ferrous wheels or brushes and we used nyon slings for casting movement to avoid carbon steel chain.

We did not experience any rust from chromium depletion caused by grinding. But we did have rust spots appear on the surface of castings stored outside for long periods in large Eastern US cities. Turned out to be from iron in air pollution.

YES.

Very strongly agree with posts 6, 7, 8, and 11. I have seen stainless steel toll booths show signs of rust from iron dust contamination from passing scrrap metal trucks (south-side Chicago, industrial pollution also). I've dealt with a large weld shop fabricater who has gone to the extreme of having separate buildings for SS and mild steel fabrication, and NOTHING passes between the two buildings.

i agree with all comments

is it possible or good to weld ms to ss pipe when there is no consideration of corrossion. if, yes which welding rods i suppose to use?

what i have to do to buff the ss tank

please guide me

Hello, You should use a E309 stick electrode or a ER309 TIG wire. Do the same prep as you would with any other welding. If you are TIG welding you will notice the stainless steel side will melt quicker and at lower amps than the carbon steel side so be careful and make sure the carbon is melting before progressing with the weld. You will have to set the machine hot enough to melt the carbon so the trick is to keep the heat on the carbon steel side or the stainless will tend to melt away. I am sure this is the case with stick welding also but you may not see this occur as much because of the nature of the flux on the electrode to turn to slag and cover up somewhat the weld. I would use stainless steel wire brush to buff the weld with. You may get a little problem of the weld rusting unless you are very careful not to buff the carbon with the same brush as you buff the stainless steel side. I have installed many of stainless steel nozzles in carbon steel tanks without any problems. One thing that can occur is galvanic corrosion between the dissimilar metals but this seems to occur more when the liquid level line is in the same area as the bimetal weld seem such as when replacing tank shell sections.

pipewelder

PLEASE THIS IS NOT A PROFESSIONAL ANSWER. THIS IS FOR THE INFORMATION PURPOSES ONLY. I AM FROM SRI LANKA.MY HOSE IS SITUATED ABOUT 1.5 KM AWAY FROM THE SEA BEACH. I HAVE IN MY HOUSE A STAINLESS STEEL STAIR CASE HAND RAIL STRUCTRE.IT IS GETTING RUSTED AT SOME POINTS IF IT IS NOT USED. I HAVE ASKED SEVERAL PEOPLE AND THEY TOLD ME THEY HAVE USED INDIAN RODS AND MALAYSIAN STUFF WANT GET RUSTED. I AM POLIHING THIS TWICE A MONTH USING BRASSO AND CAR POLISH.

From experience of 40 years in Nuclear Submarines to Tall oil,Distillation,and Resin chemical plants.You do not use grinder wheels,brushes,scrapers or chipping hammers of lesser grade material than the one you are using them on,without possible contamination.We often used 317 or better in the chemical plant.302,304,316,317,along with even more exotic metals and welding supplies were all carefully marked,segregated and stored apart to prevent mistakes and cross contamination.

You did not mention your grade of SS.My Stainless Steel firearms would rust with salt water or human sweat.alfred

"Handling or fabricating stainless steel on equipment, using tools also used for non-stainless steels should be avoided. Working in 'mixed-metal' fabrication shops, without taking segregation and cleaning precautions can result in contamination"

this is taken from

Iron contamination and rust staining on stainless steel

http://www.bssa.org.uk/topics.php?article=55

S

corrosion protection