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 subjected to the same marking. The main feature of the parameter is that it is almost never equal to the external or internal indicator.
Nominal pipe bore is an important indicator
To understand the importance of this criterion, you need to understand why it is needed and what it is.
It is necessary to start with the fact that the most common problem faced by pipeline fitters is the difference in diameter of each pipe, as well as the fittings that are used in conjunction 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 ordinary.
- The third category is reinforced pipes.
Difference in performance
It is also worth noting that the conditional pipe passage is the inner diameter of the product, which is rounded up or down, depending on which standard value is closer.
Some people have a logical question: why not use an external diameter indicator for pipes. Here you need to know that all pipelines, except gas and water, are marked in this way. But these two systems have their own specifics, which is associated with throughput based on the inner diameter. The need for a conditional passage is justified by the following. For example, there is a pipe DN 25, the outer diameter of which is 33.5 mm. The wall of such a product in its thickness may be equal to 2.8, 3.2 or 4 mm. This means that the internal value will also be different and amount to 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 25 mm in diameter. In other words, the conditional pipe pass is an average value that facilitates the selection of suitable structural elements.
What is the conditional pass indicator for?
Nominal diameter is also the nominal diameter. This value exists to describe the system. Here it is used as a characteristic feature during installation, as well as when connecting various parts of the pipeline to each other.
It is worth noting that on domestic valves, for example, installed on pipes, the conditional passage is designated as DU (conditional diameter). However, at present, most manufacturers are switching to a designation system adopted abroad. Instead of DU designation DN (nominal diameter - DN - diametre nominel). If such marking is indicated, then you need to know that the digital value can be in mm or in inches. One inch is 2.54 cm.
Throughput
An important requirement for bandwidth is that during the transition in the system it should increase by an amount that corresponds to a value from 60 to 100%. In order to achieve this indicator, it is necessary to calculate the corresponding graduation of the conditional passage for a gas pipe or water pipe. The maximum throughput will depend on the correct calculation. In other words, we have in mind the averaged design parameter for the clearance. The result must be rounded to the nearest standard value. When laying a piping system, the true level rarely matches the size of the structure. The easiest way to show this is with an example.
The outer diameter of the system is 159 mm. The pipe wall thickness is 8 mm. The true exact value of the inner diameter will be equal to 143 mm. If, for example, the wall thickness index is changed to 5 mm, then the value becomes equal to 149 mm. However, despite the difference in numerical values in these cases, the pipeline system will be marked 150.
Definition of internal dimensions
An important rule should be said right away: the actual indicator of the inner diameter of the pipe 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 outside diameter as a primary 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 figure will almost always differ from the conditional passage is that these systems will be operated in an environment with high pressure, which means that their wall thickness increases to minimize the risk of a breakthrough.
One can give an example of such a discrepancy. The outer diameter of the reinforcement is 273 mm. The actual wall thickness is 9 mm, but with these indicators, the actual indicator of the 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 for documents
As it became clear, the conditional passage (clearance, DU) is the value of the inner diameter of the pipe, taking into account the thickness of its walls. GOST 28338-89 describes all technical requirements, marking and other important parameters, including conditional pipe passage, in full. It is necessary to know this value in order to successfully create a water supply system, gas pipeline, sewage system, etc. in such a way as to have an integral structure that will not have the risk of depressurization.
This fact alone is enough to make it clear: is the most important indicator, which is necessary for arranging a reliable and working system.
Why determine the exact parameter
Some may ask: why carry out calculations to such trifles?
The answer is that knowing the exact size of the inner diameter of the pipe and the conditional passage will allow you to accurately calculate the amount of substance that this pipeline system can supply. To know and be able to calculate these details is an important skill both on an industrial scale and at home.
This skill can be useful if, for example, laying or repairing, or replacing heating pipes leading to a private house, is carried out. In such a situation, it is necessary to accurately measure all the indicators of the diameter, since the quality and uniform distribution of heat over the entire area of the building depend on this.
When arranging all 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 - increase the internal diameter, as well as increase the speed of the coolant. If we talk about the first case, then it is unprofitable, since the cost of the pipe will increase significantly with an increase in DE, which will lead to a significant increase in costs.