As a purchaser, you should always verify that the products meet applicable product standards, and to ensure that copper capillary tube you are getting is qualified is obviously an important item.
According to ASTM International and the American Society of Mechanical Engineer(ASME), some of critical requirement established, as following:
1) Dimensional Requirements--Outside diameter, inside diameter, wall thickness, insertion depth
2)Chemistry Requirements--Different tube or fitting products can be made using a number of standard copper alloy compositions.
3)Mechanical Properties--like Tensile and yield strength properties, elongation.
4)Grain Size
5)Hydrogen Embrittlement
6)Cleanliness
The points listed above represent only a portion of copper tube and fitting standards and their requirement, but the most important points we should care about.

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