Typically, expansion bellows are provided in a widely spread piping structure to reduce the stress caused by the thermal expansions in one section of the piping structure on the other section of the same structure when both the structures are anchored at their respective locations.

A centrifugal pump with a critical rotating component inside its body is firmly anchored at its foundation. The rotor balance and shaft alliance are critical for pump's reliable performance. These could be affected badly due to the thermal expansions of the piping structure connected to it, if not addressed properly. I believe the designers provide expansion bellows at both the suction and discharge side piping as a common practice.

I have seen many high temperature condensate pumps with the expansion bellows, but I couldn't recollect seeing expansion bellows near chilled water pumps, though the same theory is applicable to chilled water pumps also. This may be due to the low variation in temperature for chilled water system compared to the variation in temperature for the hot water system. It could be also due to the short pipeline lengths since the circulating pumps are located closer to the chillers.