Selection and installation of hose fittings

The metal hose joint consists of a metal tube body, a stainless steel wire mesh sleeve and a joint. In the ship pipeline system, it is mainly applied to the connection between the pipeline and the equipment where the pipeline medium is oil or fresh water, which can compensate a certain relative displacement and reduce the effect of vibration and noise. However, if the selection is not proper, not only can not achieve the effect of vibration isolation and noise reduction, but will cause pipeline leakage and even equipment failure due to the damage of the metal hose.
The selection of metal hose mainly includes the correct selection of parameters such as diameter, connection type, working pressure, temperature correction, minimum bending radius and hose length. The diameter, connection type and working pressure directly depend on the requirements of the pipeline system, generally there will be no problem, it is worth mentioning that when choosing the hose design pressure (should be greater than the system working pressure), it should not be too high, because with the pressure capacity of the hose, its bending capacity is greatly reduced. The temperature correction and minimum bending radius are fixed for the product and are given by the manufacturer. The problem we often have is the selection of the length of the metal hose, the hose is too long will cause instability, increase the flow resistance, and additional mechanical damage and vibration problems, the hose is too short may not achieve the purpose of compensation, vibration reduction and noise elimination, but also cause excessive bending stress, affecting the life. The following only describes the selection of hose lengths in two typical cases commonly used in Marine piping.
1) Axial displacement compensation
We often think that since it is a hose joint, it must be free to expand and bend, but in fact, the metal hose itself cannot be stretched axially, but the appropriate metal hose length can be selected by calculating the axial compensation amount.

2) Relative torsion occurs at both ends of the metal hose during installation. Mainly in the metal hose ends for the flange connection form, in the ship installation site, often due to installation errors, so that the connected two ends of the flange holes can not be aligned, and offset, and think that the hose joint can withstand torsion displacement compensation, but in fact, the metal hose itself can not compensate for this torsion displacement, the result is that the metal hose is twisted off. The pipeline is leaking. In this case, a metal hose with a loose sleeve flange connection can be used to connect.
3) There is a large radial deviation at both ends of the metal hose during installation. Although the metal hose itself can compensate for the transverse displacement, if there is a large relative radial displacement at both ends of the installation, it will reduce the actual compensable amount in the direction, which may cause the compensation amount required in the direction of use is greater than the actual compensable amount of the hose in this direction, so that the metal hose fatigue damage and damage.