304H oxide formation
304H oxide formation
(OP)
Recently we had several Superheater overheat failurs on a new bank of tubes. The platens are made from SA213 TP304H. They are less than 2 years old.
The failure is the result of severe exfoliation of the magnetite scale that plugged the tight radius bends and ID transitions. This stuff is very light and fragil.
I understand that this is not a new problem for the rest of the world. And with time a spinel layer will form and we will not have this problem any more.
My question is: Is there some way to prevent the magnetite formation? would passiviation have helped?
The failure is the result of severe exfoliation of the magnetite scale that plugged the tight radius bends and ID transitions. This stuff is very light and fragil.
I understand that this is not a new problem for the rest of the world. And with time a spinel layer will form and we will not have this problem any more.
My question is: Is there some way to prevent the magnetite formation? would passiviation have helped?





RE: 304H oxide formation
RE: 304H oxide formation
This particular incident we had an upset after a very long run. The upset spiked the main steam temp down which we feel is the event which dislodged all of this at once. The thermal expansion difference.
What I would like to know is what processes we could explore to prevent this r=from reoccuring on the next set of elements we make out of 304H.
RE: 304H oxide formation
We have replaced several RH and SH tube assemblies in our Power Boilers with 304H and never had an incident with serious oxide exfoliation that resulted in stress rupture failure downstream of tube bends. We are going on 10 years of operation with no problems. So, I don't see an issue related to how the tube material was supplied as long as it is supplied in accordance with ASME SA 213.
RE: 304H oxide formation
If you have a new section and the boiler runs for a long period after the installation and as a trip. The early layer of oxide comes off all at once. But if you have several small shedding events, you will not have any problem. This stuff is very fine and light. It will not get caught on screens.
But if it all comes off at once, oh boy.
ASME has nothing to do with this.
RE: 304H oxide formation
RE: 304H oxide formation