B FIGURE 4. Troubleshooting algorithm for internal fouling Internal fouling may be caused by coke formation or other material sediments (usually minerals salts dissolved in crude oil). Follow the questions below to be able to differentiate between the two phenomena. Low process-fluid flowrate is one of the main causes of internal fouling. Low flowrate can cause high skin temperature and coke buildup as a result of pyrolysis can occur. Did you experience low flowrate in one or multiple passes of your heater? No Go to Point DC Consider coke buildup with high probability. Solve the problem according to the instructions given in the burner troubleshooting guide found in Ref. 2. The fouling is 90% caused by mineral sediments. Yes Did you experience any fire-side (external side) hotspot problems (mentioned in Figure 3) like over firing or flame impingement for long periods of time? No Yes Is your fired heater in atmospheric crude distillation preheater service or is it located downstream of a de-salter? No Fouling is 90% caused by mineral sediments or even small particles carried out by fluid stream into the furnace tubes. Yes Did the fouling happened right after overhaul or upstream equipment's malfunction? No Yes If your furnace is in heavy fluid service, like vacuum-distillation-tower charge heater or visbreaker service or any vaporizing heavy feed service, consider your fouling problem as coke buildup. Caution: Coke buildup in gas reactive services like olefin plant furnaces is beyond the scope of this algorithm, look at the proper references. Follow spalling with steam procedure according to vendors instructions. Is your problem solved? Yes DC Follow spalling and decoking with steam and air procedure according to the vendor's instructions. Is your problem solved? No Consider removing and replacing the tubes with supervision of inspection department. End troubleshooting procedure. Yes If the problem is not caused by human error, then in most cases, a malfunctionhttp://www.Chemengonline.Com