The correct answer is D) superheater. Excessive foaming in a steaming boiler can cause damage to the superheater. The superheater is responsible for further heating the steam to a higher temperature and pressure before it enters the engine or turbine. Excessive foaming can lead to wet steam entering the superheater, which can cause erosion and damage to the superheater tubes. The other options are incorrect because: A) The internal feed pipe is not directly affected by foaming. B) The economizer is used to heat the boiler feedwater, not the superheated steam. C) The desuperheater is used to reduce the temperature of the superheated steam, not the superheater itself.