Shock-absorbing metal expansion joint, which pipe vibration problems can be solved?
Two days ago, I met a customer who said that the steam pipe in their workshop shook like a sieve as soon as it was turned on, and the flange gasket was changed twice every three months. In this case, the shock-absorbing metal expansion joint is the preferred option. However, many people simply understand the expansion joint as "installing it and finishing it". In fact, there are many doors here.
First, the medium pressure pulsation and fluid impact, and second, the stress generated by thermal expansion and contraction has nowhere to be released. The shock-absorbing metal expansion joint absorbs displacement through the flexible deformation of the bellows, and at the same time uses structural damping to consume vibration energy-to put it bluntly, it is not only an "expansion joint", but also a vibration buffer. The products in this station, such as general-purpose corrugated expansion joints and high-temperature axial expansion joints, are all doing this work. However, different structures should be selected for different working conditions: the temperature difference of steam pipeline is large, so the high-temperature axial type with guide tube should be selected; If the vibration frequency of the inlet and outlet of the fan is high, it is necessary to consider the double hinge type or the straight pipe pressure balance type.
Which components are playing a role in shock absorption?
The bellows is the core — its crests and valleys act like springs, transforming the expansion, contraction and vibration of a rigid pipe into its own elastic deformation. However, bellows alone is not enough. The role of tie rods and nuts is critical: tie rods can constrain excessive axial displacement, prevent bellows instability, and balance pressure and thrust at the same time. In the common question and answer, someone asked "How to adjust the tie rod nut of the expansion joint". In fact, it must be pre-tightened or loosened according to the design requirements during installation, otherwise the shock absorption effect will be greatly reduced. There is also a guide tube, which not only reduces the scouring of the bellows by the medium, but also improves the flow state and reduces the vibration caused by vortex current.
Although the flue gas baffle door and circular baffle door of this station do not directly absorb shocks, they can greatly reduce the impact of pipeline vibration on the baffle sealing surface when used with expansion joints in the flue gas system. And guess what? Many customers come up and ask "is there a general one?" The fact is that there is no general one at all, and they can only be matched by parameters.
Common pits in type selection
The most common mistake to make when selecting a model is to take a model and want to take all working conditions. For example, the air duct in the cement industry has high temperature and dust, and ordinary rubber compensators can't bear it. You have to choose the metal corrugated expansion joint in the cement industry, and you have to consider the wear-resistant lining. Another example is the desulfurization system of power plants. The flue gas is wet and contains sulfur. Rubber PTFE compensators or PTFE-lined metal hoses are more suitable-but if you use it on high-temperature steam pipes, it will be finished in minutes.
Therefore, when choosing a shock-absorbing metal expansion joint, first find out three things: medium temperature, pressure and displacement direction (axial, transverse or angular displacement). In the product list of this site, the external pressure single axial type is suitable for high frequency and small displacement, the compound hinge type can absorb large transverse displacement, and the double hinge expansion joint of air-cooled island vacuum pipeline is specialized in treating vacuum pipeline vibration.
Technical work in installation
Some say that the direction of the expansion joint arrow is the direction of the airflow? Wrong, that arrow generally identifies the flow direction or installation direction of the medium, which depends on the product manual. Others asked "Does the screw of the expansion joint need to be removed"-if it is a transport screw, it must be removed after installation, otherwise the bellows will not work properly; If it is a permanent pull rod, just adjust it in place and lock it. Then there are the expansion joints of directly buried pipelines. Like the directly buried expansion joints of this station, we must pay attention to anti-corrosion and backfilling compaction during installation, otherwise the ground subsidence will apply additional stress and the shock absorption performance will be wasted.
Fixed brackets and guide brackets must be installed on both sides of the expansion joint, otherwise the thermal displacement of the pipeline will be fully pressed on the expansion joint, and the bellows will be deformed in the slightest case or torn in the worst case.
Practical cases: power station, air-cooled island, dust removal pipeline
The temperature of the main steam pipe is as high as 540℃, the pressure is more than ten MPa, and the ordinary expansion joint is fatigued and cracked in a few months. With high-temperature axial type with guide tube, the bellows material is upgraded to Inconel 625, and the design life can be more than 10 years. Then there is the vacuum pipeline of the air-cooled island, which has negative internal pressure and vibration from the exhaust pulsation of the turbine. The traditional axial type is easy to become unstable. The double-hinge expansion joint of the vacuum pipeline of the air-cooled island is just right, and the double-hinge structure allows large angular displacement, and it also has a vacuum sealing ring.
The manual plug-in plate type insulation door is used on the dust removal pipeline with the expansion joint. When the insulation door is closed, the air flow suddenly changes the direction, and the expansion energy saves and absorbs the shock wave, so as to protect the valve from falling. What do these cases say? Shock-absorbing metal expansion joints are not panacea, but if you choose the right one, it is the "shock absorber + insurance company" of the pipeline system.
Don't think about getting it in place in one step, first find out the working condition parameters, and then match the product model. In the product list of this site, external pressure single axial type, double hinge type, high temperature axial type, straight pipe pressure balance type... each has its home field. Choose the right one and the vibration is gone, it's as simple as that.