Reducing the fatigue life of the corrugated hose compensator can greatly increase the single-wave displacement of the corrugated hose, but at the same time, the comprehensive stress of the corrugated hose is also greatly increased, which will have a great influence on the strength and stability of the corrugated hose.
The comprehensive stress and compressive strength of corrugated hose reflect both strength problems.
When the service life of corrugated hose is low, not only the meridional comprehensive stress is high, but also the circumferential stress is high, which makes the corrugated hose quickly enter the plastic deformation, leading to the instability of the corrugated hose.
For the internal pressure corrugated hose, the displacement stress forms plastic hinge at the peaks and troughs of the corrugated hose, and coupled with the pressure stress, the corrugated hose soon produce plane instability.
This is the fundamental reason why the plane instability pressure of corrugated hose with low fatigue life is much lower than that of corrugated hose with high fatigue life under displacement conditions.
From the longitudinal profile of the external pressure corrugated hose, it is equivalent to an arch beam under pressure. When working, the corrugated hose is in a stretch state, which is equivalent to the arch beam reduces the arch height, and its anti-instability ability decreases naturally.
When the single-wave displacement of the corrugated hose is too large, the flat part of the corrugated hose is inclined, which makes the peak diameter of the corrugated hose shrink, but the diameter of the peak ring is fixed. In order to coordinate the deformation, the peak collapse and circumferential instability will occur.
In summary, although no fatigue damage has been found in thermal pipe network applications to date, the design fatigue life of corrugated hose is too low, which can lead to catastrophic results.
Displacement and stability of compensator for double rod type and hinge type, the lateral displacement is realized by the deflection of corrugated hose angle, which causes the middle section to tilt.
When the corrugated hose produce angular displacement, the pressure area on the convex side of the corrugated hose is larger than that on the concave side, resulting in the addition of a transverse force to the compensator, which is easier to produce column instability than the axial type compensator. Obviously, the larger the single wave displacement of corrugated hose, the larger the transverse displacement of compensator, the more easily the column instability.
For material selection for heating pipe network of corrugated hose material, we should consider the possibility of stress corrosion, the influence of the water treatment agent and pipe cleaner on the material, etc. in addition to the working medium, operating temperature and external environment on the basis of combining with corrugated pipe material welding, molding, and the price performance ratio. Choose economic and practical corrugated hose materials.
For the trench laying of the thermal pipe network, when the compensator in the pipeline is of low terrain, rain or accident sewage will soak the corrugated hose, so we should consider the selection of materials with stronger corrosion resistance, such as iron and nickel alloy, high nickel alloy, etc.
Due to the high cost of such materials, when making corrugated hose, we should consider adding a layer of corrosion resistant alloy only on the surface that is in contact with the corrosive medium.
From the failure type and cause analysis of corrugated hose compensator, we can find the plane stability, axial stability and corrosion resistance of bellows are related to their displacement and fatigue life.
Too low fatigue life will degrade the stability and corrosion resistance of corrugated hose. According to the test and use experience, the fatigue life of corrugated hose used for heating engineering should not be less than 1000 times.
Most of the failure of corrugated hose is caused by external environment corrosion, so in the design of compensator structure, it can be considered to isolate the contact between external corrosive medium and corrugated hose.
For external axial type compensator, you can add packing seal device between the outlet ring and the outlet pipe, and its function is equivalent to the sleeve compensator, which can resist the invasion of external corrosion medium, and add a safety barrier to corrugated hose compensator. Even if the corrugated hose is broken, compensator can also play a role of compensation and to avoid corrugated hose failure.
