Is ductile iron objectionable for use in a pump bowl pumping flammable hydrocarbons ??
My perception is that ductile iron is deligated to somewhat non-hazardous applications such as water or water based fluids.
In general: Yes. The ductile iron itself is not critical. Whether or not it is resistant against chemical attack is something different and depends upon the hydrocarbons and upon the ductile iron that is used. What must be considered is the question whether there is a possible danger that sparks can occur during pumping. Is there any metal (steel) part inside the pump which can hit against the ductile iron housing and create a spark?
I believe it's a safety precaution in the event of a fire. If the ductile iron gets really hot and then hit with water, it could crack and give the fire one more fuel source.
If you have a hydrocarbon processing facility with a serious enough fire to really heat up that pump, I'd tend to think that there are bigger issues at hand but I can see where they're coming from.
Ductile Iron is not allowed in Refinery services on flammable Hydrocarbon (See API 610 10th - Annex G. The suitable selection is Carbon Steel (A216 WCB)as a minimum