Why can't the cooler line be separated from the metal expansion joint? Key Points of Model Selection and Practical Suggestions

Why can't the cooler line be separated from the metal expansion joint? Key Points of Model Selection and Practical Suggestions

The temperature difference between the inlet and outlet of their heat exchanger is almost 70 degrees, and the pipe is hard to carry without a compensator. As a result, the pipe nozzle is torn and the flange leaks, and it costs 100,000 yuan to shut down for maintenance. How much does it cost to buy a few metal expansion joints? That's enough to buy a dozen sets. This guy told me later that if he knew earlier, he would have installed expansion joints honestly.

This kind of thing is too common in cooler systems. The temperature difference between the inlet and outlet of the heat exchanger is always dozens of degrees. How much is the force of thermal expansion and contraction of the pipeline? A DN300 carbon steel pipe can generate an axial thrust of more than ten tons when the temperature difference is 70℃. Without the compensator, the nozzle weld and flange bolt can't hold it. So what exactly does the metal expansion joint do in the cooler? Not only to absorb axial displacement, but also to deal with lateral deflection and pipeline vibration. To put it bluntly, it is to leave an "expansion joint" for the pipeline, so that thermal expansion and contraction have a place to go.

1. Don't just look at the caliber when selecting the model-one of the three numbers of temperature, pressure and displacement will not work

Many purchasers come to ask for prices with the pipe diameter. I said you should give me three numbers first: maximum working temperature, design pressure and maximum displacement. I can't recommend you a specific model even if one is missing. For example, if the cooler outlet temperature is high (for example, the steam side outlet is above 150℃), then you have to go upHigh temperature axial expansion jointThe corrugated pipe must be made of heat-resistant stainless steel or heat insulation layer. While large diameter and low pressure circulating water system, withSleeve type pipe expansion jointOrStraight pipe pressure balanced expansion jointMore reliable-sleeve type is cheap and durable, and pressure balance type can eliminate blind plate force, which is suitable for large pipe diameter.

In addition, the function of the guide tube must not be ignored. It is mounted on the inner wall of the bellows, which can guide the medium to flow smoothly and prevent the high-speed fluid from directly washing the bellows. I have seen a case where there was sediment in the circulating water, and the bellows were worn out in half a year without the deflector. So ask whether the medium contains particles and what the flow rate is, which determines whether to add a guide tube.

2. The most common mistakes made at the installation site: the tie rod nut is not removed in place and the pre-stretching direction is reversed

Installing expansion joints is the same as installing equipment, you have to read the instructions. The most typical mistake is to tighten the tie rod nut as a fixing bolt. The tie rod of the expansion joint is to prevent the bellows from accidentally deforming during transportation and installation. After installation in place, the nut must be loosened so that the bellows can expand and contract freely. How to tune it? Refer to the article "How to Adjust the Tie Rod Nut of Expansion Joint" in our station, which is very clear-first loosen the locking nuts at both ends, then adjust the adjustment nuts to the design stroke, and finally don't forget to pre-stretch or pre-compress.

When it comes to pre-stretching, there are many people who have reversed the direction. The cooler pipeline is generally heated and expanded, so the expansion joint needs to be pre-stretched, and the stretching amount is equal to half of the thermal displacement amount. If it is pre-compressed, the tube will destroy the bellows as soon as it gets heated. Another, the stiffness calculation of bellows should be well informed. The stiffness is too large to absorb the displacement; The stiffness is too small, and the internal pressure will bulge. You have to ask the manufacturer for this thingStiffness and Calculation Formula of BellowsDon't blindly estimate yourself.

Third, the metal expansion joint for the cooler, should I choose the general type or the double hinge type?

It depends on the direction of the pipe and the layout of the fixed brackets. Straight pipe sections, spacious, withUniversal corrugated expansion jointThat's right. It's cheap and easy to use. However, if the pipeline has many turns, limited space, or needs to absorb large lateral displacements, then you have to go upCompound hinge transverse expansion joint。 The hinged expansion joint can only bend in one plane, but it can absorb a large transverse displacement, and is especially suitable for the bend section at the inlet and outlet of the cooler.

The space is really overcrowded?External pressure single axial expansion jointOrCurved tube pressure balance type expansion joint

And don't forget to use it with non-metallic expansion joints. For example, in the low temperature section (below 100°C), useNon-metallic expansion joint (fabric fiber expansion joint)Is cheap, corrosion resistant and absorbs vibration well. The medium contains corrosive substances (acid, alkali, brine), withRubber PTFE compensatorOrPTFE-lined hose。 The combination of metal and rubber PTFE compensators can cope with a variety of harsh working conditions.