Fabricating Rotary Kiln Shells

Generally materials are specified as "minimum" requirements. Seldom does a customer decline to get something better. As most rotary kilns are refractory lined, and it is the refractory that wears out faster, causing the shorter "kiln" life (refractory is often replaced on a periodic basis), there likely would be little difference in overall "life" of using SA 516-70 versus SA 516-60. I would recommend you look at what is most readily available. In general I believe the mills tend to make more Grade 70 than Grade 60 because it is in higher demand. Therefore, you might end up paying a premium to use Grade 60 (lower structural/mechanical properties) instead of Grade 70.

There is no problem to use ASTM A516 Grade 70 instead of ASTM A516 Grade 60 (where Grade 60 means Tensile Strength 60-80 ksi and Grade 70 means Tensile Strength 70-90 ksi) for your design of rotary kiln if you apply and use the same designed thickness.

I faced this situation many many times while I do my designs for pressure vessels (subjected to internal and/or external pressures), and I prefer to use Grade 70 instead of Grade 60, because of its higher strength which -per ASME code design calculations- leads to thinner vessel wall.