How to calculate the installation quota of metal expansion joints? Key Points Old Budgeters Won't Tell You
To be honest, many budgeters and even project managers who have just entered the industry have a big head when they encounter the installation quota of metal expansion joints. Obviously, there is a model number marked on the drawing, but the installation fee returned by inquiry can be several times different. What's the difference? Let's talk about it today.
Structural form: the first hard index, twice the difference in working hours is normal
The first hard indicator that affects the installation quota is the structural form of the expansion joint. For example, a general corrugated expansion joint (that is, our most common single axial type) and a double hinged transverse expansion joint can twice the installation time. Why? The former only twists two flanges, while the latter has to adjust the pull rod, diagonal angle, and even build temporary brackets in a small space.
For example, the large-diameter thick-walled expansion joint weighs hundreds of kilograms, so the crane shift fee has to be included, right? There are also high-temperature axial expansion joints, which must be pre-stretched or pre-compressed before installation-this process is called "cold tightening" in the quota, and the labor cost is calculated separately. So don't just look at the nominal diameter, the structural form is the first step in setting the quota.
Working conditions: Power stations and cement plants are not the same price at all
The second terrible thing is the working environment. Corrugated expansion joints used in power station industry and metal corrugated expansion joints in cement industry look similar, but the installation quota is very different. Generally, the power station has a steel frame platform, which is convenient to hoist. However, the cement plant is full of dust, so welders have to wear dust masks, and the work efficiency is at least 20% off.
More extremely, the metal expansion joint behind the desulfurization flue gas baffle door contains sulfur and humidity in the medium. During installation, the flange surface has to be treated with special anti-corrosion treatment, and the sealing gasket must be acid-resistant-this is all included in the material fee, and the unit price of auxiliary materials in the quota has to be raised. There are also directly buried (fully buried) expansion joints, which have to dig trenches, make sand cushions and restore the pavement. This part of civil engineering is often not included in the installation fee, and as a result, the settlement is strife. Therefore, before setting the installation quota, first find out the on-site working conditions.
Labor, materials and machinery: the quota is three pieces, and none of them can be missed
To be more detailed, the installation quota itself consists of three pieces: labor, materials and machinery. The labor cost is based on the unit price of regional fixed working days, but the installation of expansion joints usually requires the cooperation of fitters, welders and lifters. How many can a three-person team do a day? Take the general-purpose corrugated expansion joint of DN400 as an example. Under normal working conditions (no cold tightening and no special treatment), the skilled team can install four sets a day. But if you come across something with a flanged sealing slot like a double-sealed single-axis circular baffle door, it will take an extra half hour to clean up the debris in the slot.
The majority of materials are gaskets and bolts-don't underestimate this. There are dozens of metal-wound gaskets for high-pressure pipelines, and those with inner rings have to be used in high-temperature situations. Bolts are also divided into common carbon steel and stainless steel, and the preloading torque is different. Do you want to spread the rental fee of torque wrench? Machinery costs are most easily overlooked: electric welding machines, argon arc welding machines, and even large expansion joints have to use hydraulic wrenches, and these shift costs are a lot in a day.
Two common pits: tie rod nut and guide tube direction
Is the expansion joint tie rod nut removed or not? Many on-site maps save trouble, and they ignite directly with the transportation rod. As a result, the bellows is unstable. In fact, according to the specification, the tie rod nut should be loosened or adjusted to the designed position after installation in place-this process is called "reset", and the quota is generally separate, but many people skip it directly.
There is also the direction of the guide tube-the specific function of the expansion joint guide tube is to guide the flow direction of the medium and protect the bellows. If it is installed backwards, it will not only have no protective effect, but also cause vibration. And guess what? It's more laborious to rework than to install a new one at a time. These hidden processes are not listed in the budget, and in the end, they are all carried by the construction party themselves.
Back to the beginning: How exactly does it count? Don't set up quota subheads
How to calculate the installation quota of metal expansion joints? My advice is, don't stick with the sub-item in the local quota, that one is too thick. It is best to get specific models (such as high-temperature axial expansion joints and compound straight pipe bypass pressure balance expansion joints), let the manufacturer give an installation instruction, list the special processes item by item according to the comparison, and then adjust the artificial coefficient according to the actual site.
If you are unsure of the project at hand, ask our technical support directly. We have a database of installation hours for various working conditions of power stations, cement and desulfurization, and a phone call can help you pull out the quota details. After all, the budget saved was net profit.