Types of metal expansion joints and the working principle of each type

The answer from an expert, posted on the forum, in the hope of helping some people. 1. Expansion joints are divided into two main categories: first, those with restraining rods that can absorb the force of blind flanges ； Second, the free type ； 2. The single-type free style can only absorb axial displacement; it has blind plate force, and the pipeline requires a fixing frame. The double-type free style can absorb both axial and lateral displacements, but it also has blind plate force ； 3. Restrictive type: The compound tie rods used in the chemical industry are common; they can absorb lateral displacement and do not generate blind plate force. 4. Simple hinges (which absorb angular displacement in one plane) and simple universal hinges (which can absorb angular displacement in any plane) are capable of absorbing only angular displacement, allowing rotation around a certain angle; they are widely used in the oil refining industry. Single or single universal hinges generally appear in groups; the classic configuration consists of an L-shaped pipe fitted with three single hinges. The large tie rod absorbs lateral displacement by essentially converting it into angular displacement absorbed by a single set of waves. 5. Compound hinges and compound universal hinges, which absorb lateral displacement ； 6. There are straight (pressure-bearing) pipe types, bypass pressure-balancing types (pressure-exposed), and curved pipe pressure-balancing types. The internal pressure type is prone to instability under conditions with a high number of wave patterns and large absorption amounts; the bypass pressure-balancing type is more commonly used in flare pipelines (its advantage is the absence of blind plate forces). However, the latest flare pipeline standards, SH3009-2013, require natural compensation, and the downside of this is that it increases the required floor space. 7. Curved tube pressure-balancing type, which absorbs axial and lateral displacements. It is used at corners to balance the force of blind plates, and is commonly applied to rotating equipment. The classic one is the flue gas outlet of oil refining. 8. The external pressure single-type axial expansion joint is designed primarily because too many wave numbers cannot be used under internal pressure, as too many wave numbers can lead to instability; thus, this type of expansion joint allows external pressure to help prevent such instability. 9. When installing, each expansion joint manufacturer provides an installation manual. The restraining tie rods are colored differently from the transportation protection devices. The nuts of the transport tie rods are painted yellow; those that are not painted yellow must not be moved. 10. The manufacturer should apply paint in accordance with specifications; the transportation protection struts need to be removed before pressure testing, while the restraining struts must undergo internal pressure testing along with the pipes. 11. Free-type expansion joints should be used in conjunction with pipe fixing points; when the internal pressure reaches 1 MPA, the force at the pipe fixing brackets is approximately 30 tons. Considering that the hydrostatic test pressure is 1.5 times the normal design pressure, it can reach 2-3 times for high-temperature pipes. The force at the fixed point also increases. In that case, the fixing bracket has to be made very large, and it becomes difficult to meet the requirements from a civil engineering perspective; at such times, the designer should suggest using tie rods for transportation in order to balance the force exerted by the blind flange. Or the pressure reduction standard for hydrostatic testing. The design unit should clarify these special requirements. 12. In chemical plants, there are more pressure-balancing types with straight pipes and multi-link rod types. Straight-tube pressure-balanced two sets of working waves, one set of constant waves. The two working waves are compressed, and the planar wave is compressed. The length of the pull rod remains unchanged. The length of the tie rod from the left to the center, as well as that of the tie rod from the right to the center, remains unchanged. 13. Finally, I recommend a book titled Design and Application of Expansion Joints, authored by Niu Yuhua. There is a detailed description in the book.