Regarding the ball passage test

Coils generally have a large diameter, and low requirements are placed on pressure drop; it is sufficient to control the welding process of the pipe butt joints, and ball testing is usually not carried out. If the pipe diameter is small and high resistance drop requirements exist, a ball passing test shall be carried out in accordance with GB/T151.

I haven’t heard that coiling is required; it’s mainly for the welded heat exchange tubes.

The purpose of conducting a ball test is mainly to ensure that the flow cross-sectional area of the pipe is greater than the allowable minimum flow area. The reduction in the flow cross-section of pipes is mainly caused by forming processes (such as bending) and welding, which increases the flow resistance of the medium. Whether a ball-passing test is required depends mainly on whether the reduction in the flow cross-section caused by shaping and welding might have an unacceptable impact on the flow properties of the medium. The following are the relevant requirements for conducting a ball-passing test on boiler tubes, for reference. 1) For pipes with a nominal outer diameter of 60 mm or less, a ball test should be conducted after bending. 2) The inner diameter at the butt weld joint of the pipe shall not be less than the value specified in Table 5. Nominal inner diameter of pipe Di: Di≤25, 25＜Di≤40, 40＜Di≤55, Di＞55. Inner diameter at weld joint: ≥0.75Di, ≥0.80Di, ≥0.85Di, ≥0.90Di

This depends on whether there is splicing, as a small diameter of the elbow may cause it to collapse; in either of these cases, if it affects the fluid flowing inside the pipe, a ball test should be conducted.