It's also called welded metal expansion joint. Where is the 30% difference in quotation?
Two days ago, I ran into a cement plant project purchase, and came to me with three quotations. The same caliber and pressure, the cheapest and the most expensive are almost 30% different. He thought he had picked up a bargain, so I looked at the technical agreement and directly persuaded him to withdraw.
What's Behind the Spread? Welds are treated differently. Whether the longitudinal seam of the bellows is fully welded by argon arc welding or spot welding, whether the flaw detection is done or not, and whether the welding material matches the base metal, these links can't be seen at all by looking at the appearance alone. It is a matter of time before inferior welds crack under cyclic stress. Once the bellows cracks, the whole pipe is equal to being cut off. There is also the material of corrugated pipe, is the label 316L or the actual 304? Have you done fatigue test and hydraulic test before leaving the factory? Every saved process is changed by the life of the pipeline.
Parameter report is not complete, no matter how cheap it is, I dare not use it
Find out the working conditions first and then find the manufacturer. This sentence has been said countless times, but when it comes to the inquiry link, many people even report an approximate value of the medium temperature. Four numbers cannot be avoided in the selection of welding metal expansion joints: medium temperature, design pressure, displacement amount and nominal diameter. If one of these four parameters is missing, manufacturers can only rely on guessing. What are the consequences of relying on guessing? The number of bellows layers is too small, and it will be fatigued and fractured within a few months of operation; The thickness of the guide tube is selected thin, and the high-speed medium blows through directly.
What's more troublesome is that some working conditions are not standard working conditions in themselves. For example, the main steam pipeline of the power station has a temperature of about 600℃ and a pressure of more than ten MPa. Just put a general-purpose corrugated expansion joint on it, and the high-temperature durable strength of the corrugated pipe material can't bear it at all. At this time, the special design of the power station industry has to be used. For example, in the kiln head and tail of the cement industry, the dust is large, the temperature fluctuates violently, and the dust accumulates in the corrugated valley. Every time it expands and contracts, it is abrasive, and the life of ordinary expansion joints is directly cut in half. In this case, you have to let the manufacturer re-check according to the industry working conditions, instead of taking the sample book and turning over the model number and reporting it to you.
What do you think of the manufacturer's strength? Look for these hard goods
Many purchasing habits look at the workshop area and number of employees of manufacturers. To be honest, it is of little significance. There are three things that can really reflect the strength of welded metal expansion joint manufacturers: whether there is non-destructive testing equipment (at least X-ray or ultrasonic testing ability, not only appearance inspection); Whether the bellows is formed by hydraulic integral forming or coil plate welding-the latter has too many welds, and the risk of leakage doubles up; There are also any actual supply cases in power stations, cement and petrochemical industries, and whether there are several nameable enterprises in Party A's list.
Don't underestimate the molding process. The fatigue life gap between hydroforming and roll forming is 30% ~50% for bellows with the same thickness and material. Some small factories do not have molding equipment, so they directly purchase the semi-finished products of corrugated pipes and weld them back. The residual stress of welding is not eliminated, and it is a time bomb when loaded.
There are tricks hidden in the quotation, check item by item before payment
Quotations, laymen look at the price, experts look at the remarks. Many manufacturers will make a fuss in small print: the material column reads 316L, and the structure type is "axial type", but what you need in your working conditions is to absorb lateral displacement, which is not the same thing at all.
- Sneakily replace the 316L bellows with 304, save the material cost, and the quotation will drop.
- The direct buried (fully buried) expansion joint is marked as a general corrugated expansion joint, and the direct buried working condition is connected with ordinary products, so the external pressure and earth pressure are not counted at all.
- The structures of external pressure single axial expansion joint and double hinge transverse expansion joint are confused, and the single product is used to compensate the multidirectional displacement.
After receiving the quotation, check the material, structure and compensation amount one by one, which is better than anything else.
Installation and after-sales are more important than factory delivery
Let's say that the weld metal expansion joint is installed wrong, and the manufacturer can't save it no matter how good it is. If the flow direction arrow is installed backwards, the guide tube can't protect the bellows, and the medium directly washes the inner wall of the corrugation, which will wear out in a few months. The tie rod nut is locked when it leaves the factory, and it has to be adjusted to the working position after installation. Many people forget this step, resulting in the expansion joint completely losing its compensation ability.
So when asking the manufacturer, don't just ask how much the product costs, but ask clearly: Who will guide the installation? What are the timing and conditions for removing the tie rod? How to go about the payment process for leakage during the warranty period? Some manufacturers have a warranty of 12 months, some have a warranty of 18 months, and some promise that "during the warranty period, the bellows will be replaced directly and the disassembly and assembly costs will be borne"-the confidence and confidence of these three are completely different.
Don't listen to the sales blowing samples, go to the workshop to see the weld films
Words like "We have ISO certification" and "We are members of so-and-so association" can be written when printed on the sample. But you ask the sales to adjust the weld radiographic inspection negatives of the latest batch of products, and the ones that can be taken out happily are those that have really been inspected for quality.
Similarly, ask "Do you do hydraulic test and fatigue life sampling before you leave the factory?" You can judge a lot of things by listening to the pause and hesitation in the answer. Welding metal expansion joint is not a standard part, and it is not done by screwing on the assembly line. It carries the safety of the whole pipeline. When it comes to picking a manufacturer, efforts should be made before signing the contract, rather than waiting for the pipeline to crack before pursuing accountability for compensation.