Which of the following terms refers to the lowest part of a pipe's inner diameter?

The term that refers to the lowest part of a pipe's inner diameter is known as the Bottom of Pipe (B.O.P.). This designation is critical in pipe installation and construction as it helps in determining how the pipe will rest on a support or foundation. The B.O.P. serves as a reference point for measuring elevations and is particularly important when ensuring proper drainage and alignment in plumbing and piping systems.

In contrast, the other terms listed serve different purposes in the industry. The Center Line (C.L.) indicates the mid-point along the length of a pipe, which is useful for symmetry and alignment but does not denote the lowest point of the inner diameter. The term Slip On (S.O.) refers to a type of flange or fitting that slides onto the pipe and has no relation to measurements of diameter depth. Field Weld (F.W.) pertains to welding processes that occur on-site rather than in a controlled shop environment, which is also unrelated to the inner diameter of a pipe. Understanding these distinctions can enhance clarity and precision in piping projects.