Comprehensive Study of the Influence of Different Aging Scenarios on the Fire Protective Behavior of an Epoxy Based Intumescent Coating

Passive fire protection systems are widely used by the oil, gas, and chemical industries to protect steel against fire. However, there are concerns that the performance of these systems in a fire may be deteriorated because of weathering. Different weathering causes can modify fire performances of coatings, such as UV exposure, moisture, temperature, and immersion in a corrosive environment such as seawater. In this study, an intumescent fire retardant epoxy based coating containing ammonium polyphosphate (APP), melamine, and titanium dioxide was chosen as a model system. Primed steel plates covered with a 1500 mu m thickness coating were exposed to different accelerated aging conditions: 80% moisture atmosphere at 70 degrees C for 2 months and a static immersion bath with and without NaCl (5 g/L) at 20 degrees C for 1 month. The formulations were then tested under hydrocarbon fire conditions using a small scale furnace test developed in our lab. Immersion in distilled water for 1 month shows a slight decrease of the protective properties: On coating extreme surface, APP turns into polyphosphoric acid, which, combined with the mechanical erosion effect of water, is dissolved/detached in water. The coatings immersed for 1 month in the salted water bath show very poor protection of the steel plate, and no intumescence is observed. Sodium and chloride migrate very rapidly into the matrix. The sodium reacts with the polyphosphates to substitute ammonium species, preventing the release of ammonia during burning and thus the char swelling. As the sodium polyphosphate created is much more soluble than the ammonium polyphosphate, it dissolves rapidly inside the matrix and reduces the quantity of phosphorus. Melamine corrosion is also accelerated by the presence of chlorides. The chemical structure of the char is as a consequence different: NASICON (Na-O-P-Ti species) are created during burning, whereas only titanium pyrophosphate is created when the reference coating is burnt.