Why is the expansion joint of desulfurization flue always the first to rot? — — Find out the background of the corrosion first
The flue gas in the desulfurization flue, which sounds quite clean, is actually a "chemical laboratory"-high temperature, high humidity, and sulfur dioxide and sulfur trioxide mixed together. As soon as the flue gas temperature drops, the sulfuric acid dew point reaches, and acid liquid forms directly on the surface of the expansion joint. You said, how can ordinary carbon steel withstand this "acid bath"? In addition, the flue starts and stops frequently, thermal expansion and contraction are repeatedly tossed, corrosion and fatigue go together, and it is strange that the expansion joint does not rot first.
Therefore, the first step for anti-corrosion of desulfurization flue expansion joint is not to buy materials, but to recognize the enemy. There are only two enemies: acid corrosion and temperature stress. Find out, the rear selection, installation and maintenance are the right way.
How to choose anti-corrosion expansion joint? — — Metal lining PTFE, non-metal, rubber PTFE, who is more manufactured?
Selection is the key to anticorrosion of desulfurization flue expansion joint. If you choose the wrong material, you will have to change it in half a year. There are three common schemes on the market, you have to distinguish the occasion.
Metal-lined PTFE expansion joint
To put it bluntly, the metal bellows is lined with a layer of polytetrafluoroethylene (PTFE). Tetrafluoride is almost not afraid of any acid, and the temperature can reach about 200℃. This site'sPTFE-lined hoseAndPTFE compensatorThat's the kind. Advantages: High pressure, corrosion resistance, long life. Disadvantages: Expensive, once the PTFE layer is damaged, the acid liquid directly corrodes the metal. Suitable for occasions with high flue temperature and high pressure.
Non-metallic expansion joint (fabric fiber)
Made of multi-layer fabric + rubber + fluoroplastic composite, such as this station'sNon-metallic expansion joint (fabric fiber expansion joint)AndRectangular non-metallic expansion joint。 Advantages: Good corrosion resistance, can absorb multi-dimensional displacement, light installation. Disadvantages: Low pressure capacity, afraid of sharp objects scratching. Suitable for flues with low pressure, large diameter and not too high temperature.
Rubber PTFE compensator
Mainly rubber, lined with PTFE layer, such asRubber PTFE compensator。 Advantages: Good elasticity, strong sealing, moderate price. Disadvantages: The rubber ages quickly, and it won't work if the temperature exceeds 120℃. Suitable for flue gas pipes with normal temperature and low corrosion.
How to choose? Give you a formula: high temperature and high pressure selection lining PTFE, low temperature and low pressure non-metal, intermediate occasion rubber PTFE. Don't be cheap or over-invest.
Shake your hands when you install, and you have three years less life-these 4 details you must keep an eye on
No matter how good the expansion joint is, it will be in vain if the installation is not standardized. Desulfurization flue expansion joint is anti-corrosion, and the installation link is most prone to errors. The following 4 details, you have to keep an eye on them during construction.
- Do not install the direction of the guide tube in reverse direction— — The function of the guide tube of the expansion joint is to guide the flow direction of the medium and protect the bellows. If the direction is reversed, the flue gas will directly flush the bellows, and the corrosion will be accelerated. Remember that the direction of the guide tube arrow should be consistent with the direction of the medium flow.
- Don't screw down the tie rod nut- -The tie rod nut is used for temporary support during installation, but it must be loosened before operation, otherwise the expansion joint will not be able to expand and contract freely. Refer to the FAQ of this site "Does the screw of the expansion joint need to be disassembled?" The answer is to disassemble. Twisting too tightly is equivalent to welding the expansion joint to death.
- Insulate when welding-When installing expansion joints, flanges or pipes are often welded on site. The high temperature of welding will burn out the PTFE layer or the rubber layer. It must be separated by damp cloth or asbestos board and cooled immediately after welding.
- Reserved pre-stretch amount— — The operating temperature of the desulfurization flue is high, and the expansion joint should be pre-stretched when installed in cold state to compensate for thermal expansion. For the specific value, see the installation instructions provided by the manufacturer. Generally, the stretching amount is half of the total compensation amount.
After installation, remember to check whether the flange bolts are evenly tightened, and don't tighten and loosen, otherwise air leakage and acid leakage.
Look at three points for routine maintenance, don't wait for it to leak before you regret it
Desulfurization flue expansion joint anti-corrosion is not a matter of once and for all. If the daily inspection is in place, small problems will not drag into big accidents. You just have to keep an eye on these three places:
- Look at the surface-Are there any bulges, cracks, or corrosion spots? Non-metallic expansion joints should especially look at whether the outer fabric is aging and brittle, and whether the PTFE layer is blistered.
- Look at displacement— — The expansion joint expands and contracts during normal operation. If the bellows is found to be stuck or deformed, it means that the tie rod is not loosened, or there is a problem with the pipe support and hanger.
- Look at the fasteners-Are the bolts loose? Did the nut rust to death? Especially the bolts on the high-temperature side are easy to loosen by thermal expansion and cold contraction. Screw them again regularly, so don't be troublesome.
When a small area of corrosion is encountered, it can be repaired locally, such as wrapping with PTFE tape. But if it is a large area of perforation, change it quickly, don't wait for the leak to cause a shutdown.
Those years stepped on the pit: choose the wrong material, have to change in half a year
Two days ago, I met a customer, saying that the expansion joint of their desulfurization flue leaked after less than half a year. I asked him what material he used, and he said it was an ordinary metal expansion joint, not lined with PTFE. Tsk, isn't this soaking sauerkraut in an iron pan? Although the concentration of sulfuric acid in desulfurization flue gas is not high, ordinary stainless steel (such as 304) is still corroded due to repeated condensation. Later, they changed the sitePTFE-lined hoseOnly then did the problem solve.
Not enough layers of non-metallic expansion joints. Some factories only use two layers of cloth + one layer of rubber in order to save money, and as a result, they tear after one year of operation. The correct way is to calculate the number of layers according to the design pressure and displacement, at least four layers or more. This site'sNon-metallic expansion jointAll standard products meet the requirements, so don't downgrade them yourself.
In short, desulfurization flue expansion joint anti-corrosion this matter, select the type not to save trouble, install not to be sloppy, maintenance not to be lazy. Three steps are steady, and the expansion joint will last five or six years without any problem.