Local electropolishing, of welded area only,is the cheapest and optimal surface protection. Contact me for more information. I have been asked to quote fabrication of a chemical processing tank for a custom plating company: I. Thank you very much. Hi Michael. The short answer is 1. The slag is removed from the welds and that's usually it, with any further leaching, etc. I own a company that fabricates conveyors, platforms, and items for the food industry. We never really have a problem with any of our stainless steel, but I have noticed that in a few different rooms at different companies, some stainless steel is rusting.
It may be our stuff, it may be from another company that specializes in stainless. We currently just use scotch brite pads on die grinders, with some minor polishing compound. We have to keep everything food safe so we don't use much in the field. We always try to passivate, but our time frames may not allow that to happen. Most things are just tig welded with no sanding of welds. This allows you to do it yourself safely and with no immersion tank.
There are versions that remove rust as well as passivate that your customers can use on their affected equipment. Most of the time that will start popping up due to bleach or otherwise high chloride cleaners being used. Also unpassivated welds tend to go first, especially in instances of cross contamination with mild steel. Let us know if we can help. John, There can be some ways to solve this problem: 1.
Passivate by spraying or applying passivating gel locally you can deliver the gel and instructions to your customers. During conveyer manufacturing stage, add additional step of electropolishing it. This way you prevent ways ahead rusting problems.
See attached picture of our tests of continuous electropolishing of conveyor line. We produce welded rings made from 0. These are used in coal fired electric plants.
One of the by-products of burning coal is the production of both hydrochloric acid and sulfuric acid. These are produced in small amounts but continuously. We produce these rings from type L stainless steel. We have not been passivating the rings and the welds have been failing. Which will give us better performance, adding the passivation or adding an ecoat of Bis F epoxy? Or should we be doing both?
Hi Howard. The main reason that L exists is because of the well known problem that welding of stainless steel causes a carbon segregation that leads to attack on the welded areas. Thus, if the remainder of the object is not excessively attacked, the first thing I'd suggest is making absolutely sure your plates and welding rods are actually the correct material.
This is a sacrificial welding process using argon gas. It is a highly modified version of standard welding equipment that was developed in house and the details of which I am not permitted to disclose. But there is no welding rod or plate. We fuse the ends of the wires together. So there should be no outside contamination involved. We supply heat to the joining ends and bathe the weld area with argon gas.
I wish I could say more but I am restricted in that regard. We are running tests with L wire coated with epoxy Bis F. This adds quite a bit of cost. Indeed we are seeing costs for the passivating that are similar to the epoxy coating. So are we better served with the epoxy coating or by passivating the parts?
Pre-weld cleaning involves dressing the cut edge and removing all contaminants such as oil, paint, grease, crayon marks, adhesive tapes, etc. The area on both sides of weld should be cleaned before welding by brushing with a clean stainless steel brush and wiped with a solvent moistened cloth.
All moisture must be removed and if a flame is used care must be taken to see that any water a product of combustion does not remain on the surface or in the weld preparation. Liquid petroleum gas particularly creates a large amount of water when burnt. Each welding run must be thoroughly cleaned to remove slag and spatter before proceeding with the next run.
The cleaning method used chipping, brushing, grinding will depend on the welding process, bead shape, etc. Any cleaning equipment should be suitable for stainless steel and kept for that purpose. During welding, a gas purge on the reverse side may be advantageous.
After welding, weld spatter, flux, scale, arc strikes and the overall heat discolouration should be removed. This can involve grinding and polishing, blasting and brushing with a stainless steel wire brush, or use of a descaling solution or paste. The preferred procedure is usually dictated by end use. Grinding and dressing is to be carried out with iron-free brushes,abrasives, etc. Rubber and resin bonded wheels are satisfactory. Wheels should be dressed regularly to prevent them becoming loaded thereby producing objectionable scratches.
In any blasting process steel shot shall not be used. Efficient arc striking is essential in welding all types of stainless steels as indiscriminate arc striking tends to scar or burn the surface of the steel thus providing areas for premature chemical attack.
Care and skill are required to obtain satisfactory weld starts and restarts on continuous seams. As both burn-through on light section material and cold lack of penetration starts on heavier material can easily result from imperfect technique, the suggested procedure is to strike the electrode in the joint approximately mm forward of the actual start point.
Secondly, it enhances and speeds up the oxidation of chromium to form an inert layer, which then protects the underlying component from environmental contaminants.
After grinding, welding, cutting, and any other machining operations have been completed, the passivation processes can begin. Stainless steel itself is resistant to corrosion and rust, but several different processes can introduce contaminants that will inhibit the forming of the protective oxide layer during the fabrication process. You can say goodbye to hours of tedious work cleaning your welds with pickling paste forever once you start using the TIG Brush.
The TIG Brush effectively bypasses the safety procedures and tedious hours of time-consuming work that pickling paste requires while delivering a much cleaner and better finish that will leave your welds looking amazing and contaminant free. You or your team will be able to spend more time welding and preparing components and less time dealing with dangerous pickling paste.
The TIG Brush process is much safer compared to the hazardous process of any pickling paste application. It is time to move away from nitric acid and pickling paste, and look at the future of stainless steel passivation, the TIG Brush by Ensitech. If you would like more information on what we have discussed, feel free to reach out to us. Cougartron weld cleaning machines are designed to initiate and induce the formation of chromium oxide film on stainless steel surfaces and welds.
Thus, you can be sure that rust and other contaminating factors will not reappear after they are successfully eliminated. The heat-affected zone HAZ is an area on the metal surface whose microstructure has been altered under the influence of heat during welding. The change in the microstructure makes the steel weaker and less resistant to corrosion and stress cracking. Proper post-weld treatment cleaning and passivation is the only way to recover the structural stability of steel and prevent further decay.
But to what extent? How much of the surface do you actually need to treat? The entire metal assembly or just the heat-affected zone and the weld?
The best approach is to actively clean and passivate only the part of the surface that was actually affected by the welding process. This in all cases includes the actual weld and the heat-affected zone areas where discoloration and other post-weld imperfections usually appear.
The application of weld cleaning fluids on unaffected areas will not damage them. In any case, you will always reach parts of the metal surface outside the heat-affected zone. However, the point is that these areas do not require focused and active treatment. Although mild, acids often leave a white residue on the surface of the steel after cleaning and passivation.
Removal of these white acid marks is done for two main reasons — lowering the pH value and preserving the attractive appearance of the surface. Since the residue can sometimes become visible only after a couple of days, it is important to neutralize the surface immediately or soon after cleaning and passivation.
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