Actually, using hot water will cause the pipe to melt. If controlled properly, using hot water judiciously will enable the carver to bend and twist the shank for expressive purposes. The French had known about this for decades but jealously guarded the secret.
Alfred Dunhill learned this secret while smoking in the tub. Blissfully reading the Times while relaxing in the steaming water, he became aware that the weight of the bowl was causing the shank to bend. Realizing the enormous implications, Dunhill is reported to have leapt out of the perfumed water, sagging pipe in hand, yelling, "Egad! So that's how those damned Frenchies do it!". Thus was born the famous 120 "swans neck", well known to have been copied from a Genod design.
True story.
Oh, and hot water won't hurt a pipe. That's an old wives tale.