How to choose marine flue telescopic expansion joint? Explain from material to installation at one time
How harsh is the working environment of a marine flue? High-temperature exhaust gas (the exhaust temperature of the main and auxiliary engines is easily 400-600℃, and it can reach 650℃ in extreme cases), chloride ion corrosion in the seawater splashing area, multi-directional displacement caused by the deformation of the hull structure, and continuous vibration and thermal expansion and contraction-these factors are superimposed together, and the ordinary pipeline compensation scheme can't bear it at all. Expansion joints (also called corrugated compensators) are the vital gates of flue systems, but many people are planted in the first step: they don't know what displacement the flue should compensate for.
Are you mainly axial telescoping, or is lateral swing the majority? What is the upper temperature limit? Is the system positive or negative? These parameters directly determine what you should useHigh temperature axial expansion joint, orNon-metallic expansion joint。 Let's not flip through the sample book as soon as we get up. Let's find out the working conditions first.
Metal Expansion Joints vs Non-Metal Expansion Joints, Who Is Better for Marine Flues?
Metallic (such as those commonly used in the power station industryCorrugated expansion joint、High temperature axial expansion joint) High pressure resistance, long life, with a design life of 10-15 years, but there is an Achilles' heel-fear of chloride ion corrosion in seawater. And guess what? Two days ago, I met a shipowner with a flue temperature of 650℃. I chose a high-temperature axial metal expansion joint and added an outer sheath. As a result, the corrosion problem of the seawater splashing area was ignored, and it leaked in two years. If I had changed my thinking, usingRectangular non-metallic expansion joint(i.e.Fabric fiber expansion joint) FitDesulfurization flue gas baffle doorPartition, cheaper and durable. Non-metal has good corrosion resistance, vibration reduction and can absorb multi-dimensional displacement, but there is an upper limit of pressure and temperature resistance (generally no more than 1000℃ and tens of kPa), so it is the optimal solution in large diameter and low pressure applications.
Many people think that non-metallic expansion joints are "low-end goods". In fact, non-metals are the mainstream for marine rectangular flues (especially wet flues after desulfurization). Metal expansion joint is difficult to install large diameter rectangular flue, and welding deformation and stress concentration are pits. The non-metallic fabric layer can automatically adapt to the deformation of the hull. Do you think it is fragrant?
You can't just look at samples when selecting, but the core parameters have to be dead
Temperature, pressure, caliber, displacement-these four are hard indicators. Take the flue of marine main and auxiliary engines as an example. The common temperature is 400-600℃, and the pressure is from several kPa to tens of kPa, but the displacement is very complicated: hull deformation plus thermal expansion may require ±50mm in axial direction and ±20mm in transverse direction. At this time, it is often not enough to rely on one expansion joint alone, so it has to be used in combination. Such as usingStraight pipe pressure balanced expansion jointSpecially absorbs axial displacement, and then matchesCompound hinge transverse expansion jointHandles angular swings. Note: Never forgetexpansion joint guide tube！ The function of the guide tube is to protect the bellows from high-speed smoke, and the marine flue must be added, otherwise it will wear out in half a year-that thing is worn out, and the bellows is directly exposed to the exhaust gas, so it is a matter of time before air leaks.
In addition, if the flue needs frequent maintenance and isolation, packaging and purchasing can be considered simultaneously during model selectionDouble-sealed single-axis circular baffle doorOrManual plug-in insulation door。 The double seal structure can prevent smoke from flowing back, and there is no need to stop the machine when repairing the expansion joint, thus saving major problems.
What are the pits for installation and routine maintenance?
Look firstHow to adjust the tie rod nut of expansion joint— — The tie rod is locked when it leaves the factory, and the nut must be loosened to leave a compensation margin after installation. Many people missed this step, and as a result, the bellows could not expand and contract freely, and was forcibly cracked. Exit! In additionArrow direction of expansion jointIt refers to the flow direction of the medium. Don't install it backwards. If it reverses the direction of the guide tube, it will become internal pressure and external blowing, which will not work at all.
The fabric layer of non-metallic expansion joint is easy to accumulate dust, especially the flue gas of diesel engine contains oil and carbon, and the skin surface will be scaled over time. It is recommended to check regularly and cooperate withManual plug-in insulation doorDo partition overhaul. If the system requires automatic control,Electric plug-in insulation doorAlso standard. And,Desulfurization flue gas baffle doorUsually, zero leakage is required. When buying this thing and expansion joints in packages, confirm the seal grade and drive mode.
Common faults and what to do?
Leaks are the number one fault. Most of the reasons are that the tie rod is not adjusted properly during installation, which causes the bellows to twist, or the non-metallic skin to age. Mismatched bellows stiffness can also cause problems-too stiff to absorb displacement, too small and easy to destabilize. ThenService life of expansion jointHow long, exactly? The design life of metal bellows is 10-15 years, but it is greatly affected by the actual working conditions: frequent hot and cold cycles and seawater corrosion will break the life span. If you are not sure if you should replace it, check the bellows with the naked eye for cracks, deformation, or delamination of the non-metallic layer. A lot of other people askDo you need to remove the screw of the expansion joint？ Note: Only the transport screw needs to be disassembled, and the positioning screw does not need to be disassembled after adjustment-it will lose its limiting function when disassembled, and the expansion joint is easy to be damaged by excessive displacement.
Don't just look at the price when choosing a model. A ship has been operating normally for 20 years, and the labor and lost work cost of repairing the expansion joint once in the middle is enough for you to change three sets of high-quality products. Find a reliable supplier, give all the working conditions parameters, and let professional people do professional things, which is much more reliable than thinking about it yourself.