Before disconnecting a joint in a pipeline, you should be sure no pressure exists in the line. Joints in pipelines must be properly aligned before they are connected, misalignment will cause excessive strain.
USCG Book 11 Question No.989
As shown in the illustration, a section of 4.5 inch standard weight, seamless steel pipe, has a wall thickness of .355". When the pipe is bent 90° the length of the outside 'A-B' will exceed the length of the inside 'C-D' by ____________.
The radius of the outer edge (A-B) of the bend will be greater than the inner radius (C-D) by the inner diameter of the pipe plus twice the wall thickness (ignoring deformation during the bending process).
Since the full 360-degree circumference of the circle would be 2*p*r, one fourth of that (90°) would be 0.5*p*r
Inside diameter of 4-1/2 inch standard (schedule 40) pipe = 4.5
The difference in two radii (4.5+0.355+0.355) = 5.21
The difference in the arc lengths would be 0.5*p*5.21 = 8.184 inches.