People who deal with the pipeline know that the conditional passage of the pipe is a parameter that marks water and gas pipelines. In addition, steel pipes and fittings are subject to the same marking. The main feature of the parameter is that it is almost never equal to the external or internal indicator.
The conditional passage of the pipe is an important indicator
To understand the importance of this criterion, you need to understand why it is needed and what it is.
To start with, the most common problem pipe installers face is the difference in diameter between each pipe and the fittings that are paired with it. The thing is that pipes for gas or water can be divided into three groups depending on their strength.
- The first category is the lungs.
- The second category is commons.
- The third category is reinforced pipes.
Difference in performance
It is also worth noting that the nominal diameter of the pipe is the inner diameter of the product, whichrounded up or down, whichever comes closest to the standard value.
Some people have a logical question: why not use an external diameter indicator for pipes. Here you need to know that all pipelines, except for gas and water, are marked in this way. But these two systems have their own specifics, which are related to the throughput, based precisely on the internal diameter. The need for a conditional pass is justified as follows. For example, there is a pipe DU 25, the outer diameter of which is 33.5 mm. The wall of such a product in its thickness can be equal to 2, 8, 3, 2 or 4 mm. This means that the internal value will also be different and be 27.9, 27.1 and 25.5 mm, respectively. However, it is immediately important to note that all three types of construction will be fully compatible with pipe threads, the diameter of which is 25 mm. In other words, the nominal diameter of the pipe is an average value that facilitates the selection of suitable structural elements.
Why is the conditional pass indicator needed
Nominal passage is also a nominal diameter. This value exists to describe the system. Here it is used as a characterizing feature during installation, as well as when connecting various parts of the pipeline to each other.
It is worth noting that on domestic shut-off valves, for example, installed on pipes, the nominal passage is designated as DN (nominal diameter). However, at present, most manufacturersswitch to the designation system adopted abroad. Instead of DN, the designation DN (nominal diameter - DN - diametre nominel). If such a marking is indicated, then you need to know that the digital value can be in mm or inches. One inch equals 2.54 cm.
Throughput
An important requirement for throughput is that it must increase by an amount that corresponds to a value between 60 and 100% as the system transitions. In order to achieve this indicator, it is necessary to calculate the appropriate nominal bore graduation for a gas pipe or a water pipe. The maximum throughput will depend on the correct calculation. In other words, this refers to the average design parameter for clearance. The result must be rounded to the nearest standard value. When laying a piping system, the true level rarely corresponds to the size of the structure. The easiest way to show this is with an example.
The outside diameter of the system is 159mm. The wall thickness of the pipe is 8 mm. The true exact value of the inner diameter will be 143 mm. If, for example, you change the wall thickness to 5 mm, then the value becomes 149 mm. However, despite the difference in numerical values in these cases, the piping system will be marked 150.
Determination of internal dimensions
Immediately it is worth saying an important rule: the actual indicator of the inner diameterpipes will directly depend on the actual values of the wall thickness of the product. This is important, since all remaining dimensions for gas and water systems will be determined in accordance with it. Other systems use the outer diameter as the main indicator. It is also important to understand that steel materials are used here, which means that their size will always be constant. The reason that the actual value will almost always differ from the nominal diameter is that these systems will operate in a pressurized environment, which means that their wall thickness is increased to minimize the risk of a breakthrough.
An example of such a discrepancy can be given. The outer diameter of the reinforcement is 273 mm. The actual wall thickness is 9 mm, but with such indicators, the actual inner diameter is 255 mm. What is the nominal diameter of the pipe in this case? It is equal to 250 mm - this is the nearest standard value.
Setting parameters according to documents
As it has already become clear, the nominal bore (clearance, DN) is the value of the inner diameter of the pipe, taking into account the thickness of its walls. All technical requirements, marking and other important parameters, including the conditional passage of the pipe, GOST 28338-89 describes in full. Knowing this value is necessary in order to successfully create a system of water supply, gas pipeline, sewerage, etc. in such a way as to have an integral design that will not have the risk of depressurization.
This fact alone becomes enough to make it clear: remote control is the most important indicator that is necessary for arranging a reliable and working system.
Why define the exact parameter
Some may ask: why do calculations down to such trifles?
The answer is that knowing the exact size of the inner diameter of the pipe and nominal size will allow you to accurately calculate the volume of substance that this piping system can deliver. Knowing and being able to calculate these details is an important skill both on an industrial scale and at home.
This skill can come in handy if, for example, you are laying or repairing or replacing heating pipes leading to a private house. In such a situation, it is necessary to thoroughly accurately measure all diameter indicators, since the quality and uniform distribution of heat over the entire building area depends on this.
When arranging the same heating, you will also have to figure out what the heat flow is and how to increase it. There are two ways to do this - an increase in the inner diameter, as well as an increase in the speed of the coolant. If we talk about the first case, then it is unprofitable, since the cost of the pipe with an increase in the remote control will increase greatly, which will lead to a significant increase in costs.
