Why is temporary restraint needed for expansion joints before pressure testing?

Because the test pressure is higher than the design pressure, the purge flow rate is higher than the flow rate of the working medium.

Let’s start by explaining what an expansion joint is. An expansion joint is also commonly referred to as a telescopic joint or a bellows compensator. It is a compensation device that makes use of the elastic deformation of its bellows elements in order to absorb the dimensional changes that occur in pipelines, conduits, or containers due to factors such as thermal expansion and contraction; it constitutes a type of compensation element. It can absorb axial, lateral, and angular displacements, and is used to address thermal and mechanical displacements in pipes, equipment, and systems, as well as to absorb vibrations and reduce noise. In production, expansion joints installed on pipes must be selected based on the specific manufacturing processes; their compressive strength must be lower than that of the pipes, otherwise they will not fulfill their intended function. When conducting pressure tests on systems, the pressure applied must be close to the maximum pressure that the pipes can withstand, which is much higher than the operating pressure during normal production. As a result, the expansion joints are prone to damage under such pressure. To protect them, it is necessary to apply temporary constraints to the expansion joints during pressure tests

It is true that the test pressure is much higher than the operating pressure, but to what extent does adding constraints help improve the pressure-bearing capacity of expansion joints? If it can’t withstand the pressure, it’s safer to simply disconnect it from the system. But the specifications state that temporary constraints should be added; I think there must be some other reason. What was said on the 5th floor makes sense, but I still don’t quite understand what specific reasons or mechanisms caused the water pump to be moved. This post was last edited by zhanong on 2008-1-19 12:25.]

Under internal pressure, bellows expansion joints generate a significant pressure thrust (Fp = P*A, where P is the internal pressure)； A is the effective area of the bellows, and A is approximately 1.2 to 1.5 times the cross-sectional area of the pipe ； For example, in a DN1000 hot water pipeline with a design pressure of 1.6 MPa, if the test pressure is 1.5 times the design pressure, that is 2.4 MPa, then Fp equals 271 tons of force, and the direction of this force is outward along the axis of the bellows expansion joint. Without any constraints, this force will act on the fixed bracket. Fixed supports are generally designed based on the design pressure, and they cannot withstand the thrust generated by the test pressure. If no temporary restraints (or reinforcing brackets) are used, the result is that the fixing brackets are pushed over or deformed, while the bellows expansion joint is stretched and rendered unusable. A better approach is to first install and weld the entire pipeline, and then complete the pressure testing. Cut off another section of pipe according to the length of the bellows expansion joint, and install the bellows expansion joint at the cut site (the bellows expansion joint has generally undergone a pressure test at 1.5 times the design pressure before leaving the factory); this practice is widely used in practice. It should be noted that the bellows expansion joints mentioned above refer to those that do not come equipped with their own restraining devices. For bellows expansion joints equipped with their own restraining devices, such as those of the large tie rod transverse type, hinge type, pressure balance type, etc., it is not necessary to install temporary restraints during pressure testing. Feel free to contact us at ssong_zhiguo@126.com

Simply put, temporary restraint is applied to the expansion joints only during pipeline pressure testing. The main purpose of this is to prevent the expansion joints from expanding beyond their allowable limits as a result of pressure, which could cause them to stretch and deform. Expansion joints are quite expensive; each one usually costs several hundred to over a thousand dollars. I remember once, during the pressure testing of a heat transfer oil pipeline, the quality of the welding used for the temporary restraint devices was poor, leading to the failure of those devices during testing. As a result, the expansion joints were stretched so much that they could not return to their original shape and had to be discarded.

Coming to obtain the scriptures:lol:lol:lol

Is the restraining device intended for the expansion joint or to protect the pipeline? After reading everyone’s replies, it seems that temporary restraining devices are meant for the expansion joint itself, rather than for anything outside of it.

It’s still for the pipeline, essentially, right?

It is necessary; if there are constraints on u, the expansion joint will deform severely and get damaged during pressure testing