The acetic acid pipeline in the chemical plant is the most important process pipeline in the chemical plant. The original design of the acetic acid pipeline in a chemical plant is made of acid-resistant stainless steel (316L). After several years of operation, the acetic acid pipeline in the oxidation section is corroded seriously, and many pipelines are corroded It affects normal production and even causes accidental parking. The leaked acetic acid gradually corrodes nearby steel structures and equipment, seriously pollutes the environment, and poses a serious threat to personal safety.
After analyzing the causes of pipeline corrosion, it was found that the concentration of acetic acid in the chemical plant was as high as 99.5%. After the acetic acid molecules in the acetic acid pipeline were heated, the temperature increased and the activity increased, which caused serious corrosion to acid-resistant stainless steel pipes. There are some pipelines. Although the concentration of acetic acid is low, due to the small amount of hydrobromic acid (HBr), the pipeline is still severely corroded. The wall thickness of the pipeline is thinned seriously, which poses a hidden danger to the safe production of chemical plants. Therefore, since 1997, the 316L acid-resistant stainless steel pipes of the chemical plant have been gradually replaced with titanium pipes. The operation effect has been very good for more than 4 years after the replacement, which has created a safe, stable, long, full and excellent operation of the chemical plant. good conditions. This article mainly describes the production, installation process and technical essentials of titanium tubes.
After the arrival of the titanium tube, the owner, the person in charge of the construction, the construction worker, the quality inspector, and the welding technician should be organized to inspect the material, specifications, quantity, quality, and quality certification documents of the pipe and valve parts. The pipe must have a factory certificate and quality certificate. And the outer diameter and wall thickness should be measured one by one, and the outer diameter, wall thickness and ellipticity must meet the specifications. The inner and outer surfaces should be smooth and clean, free of defects such as pinholes, cracks, folds, and excessive corrosion.
Titanium tubes should be placed according to the same requirements during transportation. In the lifting process, nylon or synthetic fiber slings should be used. If steel wire ropes and shackles are used, they shall not be in direct contact with the pipeline, and rubber or asbestos products shall be used for isolation.
Titanium tube with good material, the caliber is smaller, it is best to go to the lathe to make the bevel, the lathe speed should be slow, and pay attention to cooling. For larger calibers (above DN100), it is advisable to use a polisher to polish the groove. The speed should be slow during operation, and should be done in several times, and pay attention to cooling. When approaching the requirements, use a fine tooth file to remove the contaminated layer until the groove requirements are met. The surface of the groove should be smooth, free of cracks and heavy skin, and thoroughly remove burrs, ballast and oxides. The angle of the groove should meet the requirements of the welding process. After the processing of the groove, pickle and clean within 50mm on both sides of the groove. Then seal it with plastic cloth and mark it well. When grinding and cutting are used, the operation should be performed in other places that meet the requirements. After the groove processing meets the requirements, it will be moved to a prefabricated special place.
Titanium tube construction often encounters small holes such as decondensation, discharge, and instrument source parts. It is difficult to open holes by conventional methods. Before welding the titanium tube, draw the size of the hole and the detailed and accurate position of the hole on the corresponding titanium tube. Use a lathe to drill many small holes along the centerline of the edge of the hole, the denser the better. After all drilling is completed, tap the center arc plate of the hole with a copper hammer to make it detach, and then use a special tool such as a fine tooth round file to process the hole to meet the requirements. 3 Titanium tube welding process.
Impurities such as oil stains and oxide films on the surface of the titanium tube will cause harm to the welding, and must be cleaned before welding. All welding surfaces and the surface of the parent material on each side of the weldment should be cleaned with a non-inducing wire brush within a range of at least 50 nrn The oxide film on the surface of the layered titanium tube needs to be removed before cleaning the base material with acetone. The welding wire must also be cleaned. The processed weldments and welding wire should be paired and welded immediately. If the placement time exceeds 2h, the above process must be cleaned again. At the same time, the operator must wear clean gloves during the welding process. The welding environment should be clean and the wind direction and wind power are appropriate to reduce the dust in the air to protect the sides of the groove and the welding wire.
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