Modelling breakdown of industrial thermal insulation during full-scale jet fire exposure

Equipment and piping containing pressurized flammable gases and liquids represent a significant hazard when exposed to jet fires. To prevent escalation, thermal insulation is often combined with a layer of passive fire protection (PFP). Previous small-scale jet fire tests of thermally insulated steel structures indicated that the insulation alone, during exposure to temperatures above 1200 °C, could keep the temperature of the steel below 400 °C for at least 20 min. In the present study, full-scale jet fire exposure was modelled. The set-up included a 6″ pipe, 25 mm air gap, thermal insulation and a weather protective cladding. Thus, the article presents the numerical model including thermal insulation break down, alone or combined with layers of PFP. The modelled results were compared to results from a full-scale jet fire test of a thermally insulated pipe. The agreement between modelling and the full-scale jet fire test was quite good considering the variations along the tested pipe. The modelling does, however, show that small variations in the properties of the thermal insulation can result in major differences when exposed to jet fire conditions. Horizontal shrinkage, creating gaps in the insulation was the prevailing degradation mechanism for temperatures above 1100 °C. Oven testing of 50 mm cubic insulation specimens, proved to be useful for evaluating the thermal insulation behavior and improving the numerical model. Modelling showed that adding a 25 mm layer of PFP just beneath the weather cladding significantly improved the situation. This should be confirmed in a full-scale jet fire test.