Shell and tube heat exchanger in production, tube plate and the tube welding by manual arc welding, weld shape exist varying degrees of defects, such as depression, porosity, slag, the weld shall be the force distribution is not uniform. When used, the tube plate is generally in contact with industrial cooling water, and impurities in industrial cooling water, salt, gas and microorganism can form corrosion of pipe plate and weld. This is what we often say that the electrochemical corrosion. The study shows that the industrial water, whether it is fresh water or sea water, can have all kinds of ions and dissolved oxygen, which changes the concentration of chloride and oxygen, which plays an important role in the corrosion of metal. In addition, the complexity of the metal structure will also affect the corrosion morphology. Therefore, pitting corrosion and crevice corrosion are the main corrosion of tube sheet and tube weld. From the outside, there will be a lot of corrosion products and products of the surface of the tube plate, the distribution of the size of the pit. By using sea water as medium, can generate galvanic corrosion. Chemical corrosion is the medium of corrosion, heat exchanger tube plate contact with a wide variety of chemical media, will be the corrosion of chemical media. In addition, the heat exchanger tube plate and the heat exchange tube will produce a certain double metal corrosion. Some of the tube sheet is still in the erosion of the medium of corrosion. In particular, the fixed tube plate heat exchanger, as a result of temperature stress, the tube plate and the heat exchanger tube connection is very easy to leak, resulting in the failure of the heat exchanger.
In summary, the main factors that affect the corrosion of tube plate are:
(1) the composition and concentration of the medium: the influence of concentration is different, for example, in the hydrochloric acid, the more serious the general concentration is, the more serious the corrosion is. Carbon steel and stainless steel in the concentration of 50% sulfuric acid in the most serious corrosion, and when the concentration increased to more than 60%, but the sharp decline in corrosion;
(2) impurities: harmful impurities, including chloride ions, sulfur ions, cyanide ions, ammonia ions, etc., these impurities in some cases will cause serious corrosion;
(3) temperature: corrosion is a chemical reaction, the temperature of each increase of 10 degrees Celsius, corrosion rate of about 1~3 times, but there are exceptions;
(4) pH value: the smaller the average pH value, the greater the corrosion of metal;
(5) flow rate: in the majority of cases, the greater the flow rate, the greater the corrosion.
At present, the polymer composite material for corrosion protection, which has excellent adhesive properties and temperature resistance, chemical corrosion resistance, the material is 100% solid, no volatile substances, can be used safely in a closed environment and not shrink, especially good corrosion resistance and excellent corrosion resistance of the material, the corrosion leakage of the repair parts, can provide a long-term protective coating.
Tube sheet protection operation process:
1, tools and equipment: drill sandblasting equipment, the protection of canvas or plastic, cork, alcohol or acetone, scraper, a spiral device, garbage bags, flashlight, power supply, rubber gloves, safety helmet, protective glasses, rags, brushes.
Step 1: open the condenser end cap
With hair dryer and blower to dry the pipe surface and inside the water and with a cork plug nozzle and shelter the flanging, to ensure that the sandblasting processing does not damage the nozzle.
Step 2: sandblasting, sandblasting with canvas and other sheltered me, lest ejective sand dirty other devices. When the use of quartz sand blasting sand, it can produce 4 of the surface of the ear and will not produce more dust, to always play the base metal character. After blasting, the cork will be taken out.
Step 3p: solution cleaning: the metal surface impurities and oil cleaning.
Step 4: coated materials: first, polymer repair materials metal repairing material for the condenser tube plate and the inner wall of the pit sites were filled to avoid the water vortex, until it reaches the requirements plane as the standard. Then the polymer fluid protection material is applied evenly to the whole surface. Especially pay attention to the joint of the panel and the pipe to achieve the purpose of sealing and plugging.
Step 5: curing: in accordance with the curing requirements of the material to be cured, after curing can be put into production operation.
Tube sheet,Shell and tube heat exchanger