Use of a sealing material which is a multifilament or spun yarn coated with a joint sealing composition to seal a joint in a pipe system in which system a fluid having corrosion inhibitors such as diammonium dimolybdate or benzotriazole; and/or sludge removers; and/or an alcohol such as propane diol, or ethylene glycol; and/or a hydrocarbon such as diesel, including biodiesel, fuel oil, or hydraulic oil; and/or steam at a temperature of at least 180oC and a pressure of at least 10 bar (1000kPa); is to be passed through the sealed joint. It is surprising that the sealing materials of the invention can maintain a sealed joint despite exposure to such materials.