First, the premise of ranking: first distinguish the "categories" of metal expansion joints clearly
The ranking of metal expansion joints looks simple, but it is actually deep. If you search for "Metal Expansion Joint Ranking" on the Internet, the list will probably be ranked according to sales volume or brand awareness-but what does this thing have to do with your working conditions?
Also called metal expansion joint, general-purpose corrugated expansion joint, high-temperature axial expansion joint, directly buried (fully buried) expansion joint, pressure balance expansion joint... their technical parameters can be several orders of magnitude different. For an intuitive example: the design temperature of the corrugated expansion joint used in the power station industry can sometimes soar above 600℃, and the pressure level goes to PN40; However, most of the metal corrugated expansion joints in the cement industry are below 300℃ and under low pressure. If you use the general-purpose type as a high-temperature axial type, isn't that finding leaks?
So don't just stare at the rankings as soon as you get up. Start by figuring out your pipe medium, temperature, pressure, displacement type – axial, lateral, or angular? For example, the compound hinge transverse expansion joint specializes in large transverse displacement, and the curved tube pressure balance expansion joint specializes in large axial displacement plus pressure balance requirements. The ranking logic is completely different for different categories.
Second, the "ranking" often asked by customers is actually looking for cost performance-but cost performance does not only depend on price
Two days ago, I met a customer, and when he opened his mouth, he wanted to "rank first" a certain brand of general purpose, saying that it was cheap. As a result, it was used on desulfurization flue gas pipelines, and it leaked in half a year-because the corrosion allowance and lining were not considered. You say it was wrong or not? Metal expansion joint ranking cannot be separated from media and temperature.
For this thing, many people only stare at the purchase price. However, what really affects the cost are stiffness (affecting the thrust of the pipeline, and the bracket has to be thickened when the thrust is large), fatigue life (the national standard requires at least 1,000 times, but some products crack after 300 times under actual working conditions), and the design of the guide tube (the specific function of the guide tube is simply to reduce the fluid washing of the bellows, and the thickness is less than three months to wear out). These hard parameters will not be told to you on the ranking list.
3. Comparison of several hard indicators from product information
Since you want to row, you have to have a row dimension. Say a few core parameters:
- Stiffness:The stiffness directly determines the thrust of the pipe against the fixed bracket. Under the same compensation, the smaller the stiffness, the smaller the thrust, but the fatigue life may decrease. Got to balance.
- Temperature Resistance Grade:Ordinary carbon steel (≤350℃) → stainless steel (≤550℃) → superalloy (≥600℃). For example, the external pressure single axial expansion joint is usually made of stainless steel, but the double hinge expansion joint used in air-cooled island vacuum pipeline has to be made of low-temperature resistant materials, so don't get confused.
- Compensation Direction:Axial, transverse, angular. The lateral expansion of compound hinges saves energy and absorbs large lateral displacements, but is not good at axial compensation; Curved tube pressure balance expansion joints, on the contrary, are suitable for large axial displacement and can balance pressure and thrust.
Which ranks higher? Depends on your pipe layout. For example, steam pipeline, with large axial displacement, is suitable to use straight pipe pressure balance expansion joint; Smoke exhaust pipe, with many lateral displacements, consider the lateral type of double hinge. There is no almighty "first place".
4. Don't ignore the accessories: pull rod, guide tube, baffle door
Some manufacturers keep the price of expansion joints very low, but cut corners in the thickness of the guide tube, or the material of the tie rod adjustment nut is galvanized steel instead of stainless steel. And guess what? Not long after installation, the nut stuck, the guide tube was punched through by the medium, and the whole system had to be shut down for maintenance.
The ranking of metal expansion joints should be integrated with supporting quality. For example, when the flue gas baffle door and the expansion joint are used in combination, the sealing performance directly affects the overall performance of the system. The actuator life and sealing surface material (double seal design or single seal) of electric plug-in insulation door have to be looked at as a whole. There is also a manual plug-in type insulation door. Although the structure is simple, the operation torque will cause stuck…These details will not be written in the ranking list.
Before signing the contract, let the supplier write clearly the material grade and thickness of the guide tube of the accessories. Don't save that little money, the cost of replacing a set of baffle doors later is much more expensive than buying the expansion joint itself.
5. Real case: domestic substitution for import, cost reduction by 30%
The original design of a power plant used an imported brand of metal expansion joint, which ranked high indeed, but the delivery time was 8 months, and the price was ridiculously high. Later, it was replaced with a domestic straight pipe pressure balance expansion joint, and its performance was fully up to standard: under the same working conditions, the fatigue life was 1,200 times (the national standard was 1,000 times), and the stiffness error was controlled within ±5%. The cost dropped by 30% directly.
Ranking is not a superstition, it is a match. If you insist on using non-metallic expansion joints (fabric fiber expansion joints) on high-temperature oil pipes, there will definitely be a problem-people's fabric fiber expansion joints are for flue gas pipes, and the design temperature generally does not exceed 400℃, and the oil pipe temperature may be higher, and the oil permeability is strong, so the fabric fibers will be swollen and failed. Similarly, the rubber compensator is not suitable for high-temperature acid gas environment, so it is necessary to use PTFE-lined metal hose or PTFE compensator.
Therefore, before selecting, take a piece of paper to list clearly: medium type, temperature range, pressure grade, displacement direction and quantity, environmental corrosiveness. Then find the corresponding categories from the product list of this site-general corrugated expansion joint, high-temperature axial expansion joint, directly buried (fully buried) expansion joint, compound straight pipe bypass pressure balance expansion joint and so on. Don't be led by the "ranking".