According to the close arrangement of circles (as shown in the picture), the diameter you want is not a definite number, because you can't tie it into a circle, so there will be small protrusions.
According to the dense packing, your circular tube should be able to wind 6 times (any circle in the figure is the center, 7 blocks use 2 times, and 19 blocks use 3 times). . . ), 9 1 root canal is occupied at this time, and the remaining 9 canals are evenly distributed on the surface, which affects the overall diameter by about 10mm (or divided by 2).
The total diameter of the six steel pipes is 2*6* 10+5= 125mm.
So the diameter you require should be between 125mm and 135mm, because it is not a perfect circle, so it only has a large range.