Color issues with stainless steel storage tanks
Thread Content
Today, a colleague suddenly asked me why paint is applied in some areas of stainless steel pipes. As shown in the picture, why is this? It seems that one is 304 and the other is 316. Are there any standards to follow in this regard?
The flange is likely not made of stainless steel, so it needs to be painted.
There are many stainless steel painted products abroad, especially in Japan. But it is still rare for one flange to be brushed while another is not. I wonder if it could be due to galvanic corrosion? Electrochemical corrosion can occur, in particular, between flanges made of different steel types. But it seems that there isn’t such a large potential difference between 304 and 316. I don’t understand it; those who are knowledgeable please give me some guidance.
This red one should be a carbon steel high-neck butt-weld flange, with a stainless steel lining inside and on the sealing surface.
Is it a butt weld between a carbon steel long-neck flange and a stainless steel short sleeve, with the short sleeve also being butted to the head? Can stainless steel and carbon steel be welded directly together?
I saw it once before, in products designed for low temperatures; the stainless steel used in such products is usually not painted. After painting, due to the large temperature changes when liquid enters and exits the product, the paint tends to peel off easily. However, in some cases painting is still done, and that is because there are certain applications where painting is required in combination with stainless steel. Paint is applied for aesthetic reasons as well, sometimes using a color that matches the surrounding surface. But the requirements for paint are higher.
To control galvanic corrosion, insulating gaskets should be placed on both sides of the bolts, and the bolt shafts can be coated or fitted with insulating sleeves; plain paint is ineffective. As can be seen from the diagram, it should be as mentioned on the 4th floor, with a carbon steel lining used to save costs. In my opinion, painting the outer surface of stainless steel is mainly done to take into account environmental factors, such as locations near the sea or areas where chlorine leaks occur, in order to prevent corrosion by chloride ions in the air. I’ve never encountered one that was painted just because it looked good.
The flange that was painted is clearly a stainless steel lined weld flange, with leak detection holes on it as well
Could it be galvanic corrosion? A potential difference between some dissimilar steels can cause electrochemical corrosion.
This guy really looked closely; I agree!
“\"Paint is applied to certain parts of the stainless steel pipes,\" probably to use color to identify the medium inside the pipes. In the rooftop photos, why are the fasteners on the flange painted? Threads should generally not be painted.