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Carbon steel pipe,Seamless steel pipe,Welded steel pipe

38 Terms for Pipes and Fittings (1)


01. Nominal diameter (DN):

The nominal diameter of the pipe in the thermoplastic pipe system, indicating the size of the inner diameter and outer diameter of the pipe or its approximate value.

02. Circumferential bending stiffness / Circumferential stiffness:

A measure of the ability of the pipe to resist circumferential deformation. It can be determined by test methods or calculation methods, with units of N/m2 or KN/m2.

03. Elastic diameter deformation rate:

The ratio of the value of the vertical elastic deformation of the pipe diameter under the external pressure load to the central axis diameter of the pipe wall section before loading. It is expressed as a percentage and determined by the flattening test.

04. Out-of-roundness:

The difference between the maximum outer diameter and the minimum outer diameter measured at the same cross section of the pipe.

05. Standard dimension ratio (SDR):

The ratio of the nominal outer diameter of the pipe to the nominal wall thickness. SDR=DN / en.

06. Maximum operating pressure (MOP):

The maximum effective pressure of the fluid allowed to be used continuously in the pipeline system, in MPa.

07. Nominal wall thickness en:

The specified value of the pipe wall thickness, in mm.

08. Total use (design) factor C:

A total factor with a value greater than 1, which takes into account the use conditions and the properties of components such as fittings in the pipeline system that are not reflected in the predicted lower limit.

09. Predicted hydrostatic strength lower confidence limit (σLPL):

When the confidence level is 97.5%, the lower limit of the predicted value of hydrostatic strength corresponding to temperature T and time t, σLPL=σ(T, T,0.975), in MPa.

10. Minimum required strength (MRS):

The stress value obtained by rounding the value of the 20℃, 50-year confidence lower limit σLPL down to the nearest priority number according to the R10 or R20 series, in MPa. When σLPL is less than 10MPa, it is rounded according to the R10 series. When σLPL is greater than or equal to 10MPa, it is rounded according to the R20 series.

11. Design stress σs:

The allowable stress under the specified application conditions, MRS divided by the coefficient C, rounded to the next smaller value in the priority number R20 series, that is, σs=[MRS] / C.

12. Allowable deviation / limit deviation:

The deviation between the allowable limit value and the specified value. The difference between the maximum allowable value and the specified value is called the upper deviation, and the deviation between the minimum allowable value and the specified value is called the lower deviation.

13. Tolerance:

The deviation allowed by the specified value is expressed as the difference between the maximum allowable value and the minimum allowable value. Equal to the difference between the upper and lower deviations.

14. Outside diameter at any point:

The outside diameter measured through the cross section of any point of the pipe, in mm.

15. Average diameter:

The diameter corresponding to the center circle of the pipe wall section. The average diameter is equal to the difference between the average outer diameter and the average wall thickness, or the sum of the average inner diameter and the average wall thickness, and the unit is mm.