Abstract: Cryogenic fluids are used to remove contaminants such as hard scale deposits from heating and/or heat transfer equipment. The fluid may be cryogenically cooled to achieve a liquid phase and/or a mixture of liquid and gas phases. The fluid may also be pressurized. The mixture does not include a solid phase. A particle injection port is not required. The cryogenic fluid contacting the surface of a scale or other contaminant that has built-up during service of heating or heat exchanging equipment causes a near instantaneous contraction at the scale surface. Cracks form at the scale surface contacted by the cryogenic fluid. These cracks extend through the scale thickness to the underlying material of the equipment of the heating and/or heat exchanging component. The fractured surface scale separates by spalling or de-cohesion from the underlying equipment structure and is moved off the surface by the action of the exiting cryogenic fluid.