Types of refrigeration and air conditioning piping and calculation formula for wall thickness

Types of refrigeration and air conditioning piping and calculation formula for wall thickness Types of refrigeration and air conditioning piping

The types of refrigeration and air-conditioning piping are classified into the first, second, and third types according to the highest operating pressure (design pressure).

Type 1: Design pressure (3.45MPa) equivalent to R22 (including R407C, R404A, R507A)

Type 2: Design pressure equivalent to R410A (4.15MPa)

The third type: (4.7MPa) 5 wall thickness calculation formula

The calculation formula for the required thickness of the copper pipe (TP2M) based on the relationship of the Japanese freezing security regulations is as follows.

t= [(P×OD)/(2σa + 0.8P)] +α (㎜)

t: required wall thickness (㎜)

P: The highest operating pressure (design pressure) (MPa)

OD: Standard outer diameter (㎜)

σa: Basic allowable stress at 125℃ (N/㎜2) ＊σa = 33 (N／㎜2)

α: Corrosion thickness (㎜) * However, it is 0 (㎜) for copper pipes.

Design selection example (TP2M): The following takes O-type (TP2M) copper tube design as an example

① Wall thickness selection of exhaust pipe group of R22 refrigeration system, assuming the outer diameter of the exhaust pipe group is φ19.05, the wall thickness selection method is as follows:

The maximum pressure on the exhaust side of the R22 refrigeration system is 3.45MPa, which is calculated as follows:

Wall thickness t= [(P×OD)/(2σa + 0.8P)] +α (㎜)

　　 = (3.45×19.05)/(2×33+0.8×3.45)+0

　 　=0.9558mm round off, t=1.0mm.

Note: The national standard GB/T1804 stipulates that the wall thickness deviation of φ19.05 copper pipes can be ±0.08mm, so if the supplier uses the wall thickness deviation -0.08mm to produce the tube group in order to save costs, the wall thickness will be It will be selected as 0.92mm, so the calculation result shows that when the design pressure of the pipe group is 3.45MPa, there will be a hidden danger of pipe cracking. At this time, the wall thickness of the copper tube must be appropriately increased to ensure that the tube group will not burst, or the technical requirements clearly specify that the wall thickness of the tube group is within an appropriate deviation, that is, the deviation range is within (-0.4, +0.08) mm, In order to avoid the hidden danger of tube bursting.

In fact, the maximum pressure of a generally designed R22 refrigeration system will not exceed 3.0MPa. With 3.0MPa as the design pressure and φ19.05 as the wall thickness of the high-pressure side copper pipe, the calculation is as follows: wall thickness t= [(P×OD) ／(2σa + 0.8P)] +α (㎜) = (3.0×19.05)/(2×33+0.8×3.0)+0 =0.8355mm rounded t=0.9mm, the wall thickness deviation can be set at (- 0.06, +0.08) mm, if t is 1.0mm, the wall thickness deviation will not be considered in accordance with the national standard GB/T1804.

②R410A refrigeration system exhaust pipe group wall thickness selection, assuming the exhaust pipe group outer diameter φ19.05, the wall thickness selection method is as follows: R410A refrigeration system high pressure side maximum pressure design is 4.15MPa, then its wall thickness is calculated as:

Wall thickness t= [(P×OD)/(2σa + 0.8P)] +α (㎜)

　 　=(4.15×19.05)/(2×33+0.8×4.15)+0

　　 =1.14mm round off t=1.2mm.

This wall thickness according to the national standard GB/T1804 stipulates V-level deviation can also meet the design requirements. If the tube set does not need to be bent, choosing an O-shaped tube with a wall thickness of 1.2mm will increase the cost by 20% compared to choosing an H/2 tube with a wall thickness of 1.0mm. This design is uneconomical. According to the attached table 2, it can be known that when the wall thickness of H/2 (TP2Y) copper pipe is 1.0mm, its pressure resistance can reach 6.684MPa, which meets the design pressure requirements. Therefore, in this case, the wall thickness should be 1.0 mm H/2 (TP2Y) copper pipe. It can also be calculated according to the formula. When the H/2 (TP2Y) copper pipe bears a pressure of 4.15Mpa, the required wall thickness is t=0.584mm. Therefore, the choice of H/2 (TP2Y) copper pipe with a wall thickness of 1.0mm is fully in line with the 4.15Mpa design pressure requirement, but it is a pity that H/2 (TP2Y) copper pipes cannot be bent. Through this example, we can know why some air-conditioning manufacturers’ technical information about R410A multi-line connection, why in the piping selection table, there is "φ19.05 copper pipe if the wall thickness should be 1.1mm (straight pipe) Choose 1.0mm for wall thickness)".

In practical applications, under T1 working conditions, the high pressure pressure of the R410A variable frequency system during operation throughout the year is mostly below 3.65Mpa. Taking 3.65Mpa as the calculation basis, the wall thickness t=1.0mm, but only positive deviation is allowed. At this time, the wall thickness deviation requirement should be indicated in the technical requirements. Considering safety factors, it is best to use the ultimate pressure as the basis for calculation.