Dear vs3071, Better to write full name & company. However YES, fuel oil contaminated with heavy metal has independent and cumulative effect on Heater Tube and Heater Performances. It has been studied that as independent entity V2O5 does not cause any corrosion below 590C as V2O5 must be in molten form to cause corrosion reactions. Although pure V2O5 melts at temp. above 600C, other contaminants like sodium and SOx compounds can unite with V2O5 and lowers it's Melting Point considerably. This molten V2O5 forms a slag with Heater Tubes and slag sags and run off and expose fresh heater tube metal skin to further attack. Corrosivity of fuel oil is directly proportional to Burner T and Fuel V%. A tolerable level of "V" in fuel oil is in the concentration of 20 - 150 ppm between 645C - 845C depending on Na / V ratio. So far as resistance to V2O5 is concerned 60Cr-40Ni and 50Cr-50Ni steel found to be very much suitable. Improper Firing conditions can generate local shoot-up of temp. and can enhance localised V2O5 corrosion. Combustion with low excess air reduces chances of V2O5 corrosion and combustion with very low excess air reduces chances of sulfur trioxides formation in fire box and as such the resultant Na-V complexes are less corrosive. In fuel oil ppm level of salts ( NaCl or any salts ) can enhance corrosion rate to manyfold. Sodium ( Na ) combines to form low melting sodium sulphates ( Na2SO4) which acts as catalyst to H2S or SO2 corrosion rates. Higher the Cr content of steel more sulfur conditions can be tolerated. Sulfur in any form is v. much detrimental to Ni and high Ni allyes as in burning "S"" reacts along grain boundaries to form a low melting Ni-NiS mix which causes embrittlement in-service. At T > 645C this Ni-Nis mix melts and penetrates along grain boundaries at faster rate and causes disintegration leading to ruptures. In Oxidising atmosphere NiS converts to Nickel Oxides protecting tube surface but in a reducing atmosphere attack is more. The rate of damage event by independent and in-combination is difficult to quantify in a time frame scale but lot of reasearch and development has been done by API and other Engg. Institutes in this regard. So far as effect of this fuel oil ashes and oxides on heater refractories are concerned if the ash and ash-melts can form eutectics with refractory elements then damage occurs otherwise it can only reduce the emissivity performance of refractory wall. For further guidance on "effect on refractory" it will be wiser to discuss with some refractory manufacturer Lab person. regards and others pl. comment and contribute Debasis Mitra HPL

I am just writing my perceptions. Others may pl. comment/ critics. YES V2O5 has some impact on Refractories also both wall and hearth. Normally V2O5 melts at around 680C but if traces of Sodium gets into it the melting point gets lowered. Corrosion of Metal tubes and REFRACTORIES can occur In Molten and/or semi-molten conditions of V2O5. On freeze V2O5 compunds form hard slag and act as an insulator thus restricting heat transfer and improving refractory efficiency bit and it grows by redeposition untill gravity spalling. But as it has a browny rust colour it can affect emmissivity . I am not sure whether this V2O5 reduce the melting point of Refractories or not . Better to consult a Refractory Engr. / Manufactuere and pl. do write the results in this forum. DM