Main factors affecting corrosion of tubesheet
In the last article, we introduced tubesheet. At the same time, I would like to introduce several factors that affect tubesheet corrosion. Some customers have consulted with me about tubesheet corrosion issue, so I will explain the reasons in detail today.
In the manufacture of tubular heat exchanger, manual arc welding is usually used to weld tubesheet and tubesheet. There are some defects in the weld shape, such as depression, pore, slag inclusion and so on, and the stress distribution of the weld is not uniform. When used, the tubesheet part is usually in contact with industrial cooling water, and the impurities, salts, gases and microorganisms in industrial cooling water will constitute corrosion to tubesheet and weld. This is what we often call electrochemical corrosion. In addition, the complexity of metal structure also affects the corrosion morphology. Therefore, pitting corrosion and crevice corrosion are the main corrosion types in the welds of tube sheets and tubes. From the appearance, there will be many corrosion products and deposits on the surface of tubesheet, with pits of different sizes. When seawater is used as medium, galvanic corrosion will also occur.
In summary, the main factors affecting the corrosion of tubesheet are as follows:
(1) Medium composition and concentration: The influence of concentration is different, for example, in hydrochloric acid, the greater the general concentration, the more serious the corrosion. Carbon steel and stainless steel are most seriously corroded in sulfuric acid with a concentration of about 50%, but when the concentration increases to more than 60%, the corrosion decreases sharply.
(2) Impurities: Harmful impurities include chloride ions, sulfur ions, cyanide ions, ammonia ions, etc., which can cause serious corrosion in some cases;
(3) Temperature: Corrosion is a chemical reaction. The corrosion rate increases about 1-3 times with the increase of temperature by 10 C, but there are some exceptions.
(4) pH value: the smaller the general pH value, the greater the corrosion of metals;
(5) Flow rate: In most cases, the greater the flow rate, the greater the corrosion.
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