meaning of pipeline bending

Yes. The bend will expand when hot, and contract when cool.

Bending the pipeline, thermal expansioin... not quite sure what are you asking.

But bending process does not need to be "thermal condition" that is affirmative. It's cold processing by bending machine directly, varieties of bending machine, vertical curving, horizontal curving, punching curving, and so on so forth, can you specify your question more detailed?

Are you referring to a horse-shoe loop type bending. Or a loop made locally during erection stage with 4 bends. This is for thermal expansion and is known as an "expansion loop" for pipe is metal & metal tend to expand when heated.