I have a 6.000l oil reservoir with 18 x 1000W electrical heating elements in the reservoir. The temperature of the elements is 300°C. I think this temperature is much to high and we will change the way of heating the oil (Shell Omala 220 SP2).
Oil analysis: PQ index = 2 (low) and spectrometical analysis (ICP): 1 ppm Fe. Viscosity = 86 cSt!! due to thermical cracking 300°C I think.
Analysis of the hard material around the heating elements (photo): 15.000ppm Fe, PQ index = 1170.
Is there a reason why the ferro magnetic elements like iron agglomerate around these elements?