Old boiler material

[GonzaloMartinez]

Hello everyone,

During a inspection by replica technique in a 40 year old boiler, we got to these micrographs. The first one belongs to the corrugated furnace (seems like no microstructural degradation) and the second to a ring located in the mouth of the furnace. The client provided us a sample of this material for chemical composition analysis and metalography. The results of chemistry where 0.0381 C, 0.310 Mn, <0.0100 Si, 0.0431 P, 0.0202 S. Not other elements in significant quantities. Metalography shows mainly the same microstructure in the entire thickness of the plate (1/2"), looks like ferritic matrix with massive carbides (third micrograph). Finally the question, should that material be used in a boiler furnace? could have something to do with the time of fabrication? (1975)

Thank you!

 

[mrfailure]

You should look in the ASME Boiler and Pressure Vessel Code, especially regarding material properties. Carbon steels with this chemistry can be perfectly acceptable provided they are within maximum allowable operating temperature and pressure.

 

[metengr]

I doubt the microstructure of the furnace ring was supplied in this condition from construction. The most likely degradation is spheroidization damage based on service conditions. In these situation, you evaluate the component and decide if failure will result in a forced outage or collateral damage or risk of personnel injury. If so, you should replace the degraded material, if not, you leave it in service and at some point plan to replace the ring material.

 

[GonzaloMartinez]

Thank you for your answers. Mentengr, I thought it could be something related to material provision because the rest of the material from the corrugated furnace (next replica taken 5" far from this ring, welded joint in between) shows ferrite-pearlite microstructure without degradation. I found some similar micrographs in the ASM Metals Handbook, Volume 9, belonging to a 0.06 C steel in the annealed condition. That made me doubt about this case.

 

[metengr]

GonzaloMartinez;
Thanks for the follow-up information. The description of the ring sounds vague to me as the mouth of the furnace. If this is the case, I would still think that radiant heat or flue gas impingement even only 5" away can result in spheroidization damage after 40 years of service especially on unprotected surfaces. Was there refractory on this ring material?

 

[GonzaloMartinez]

Sorry, I couldn´t find the words to explain it, maybe with a picture. The red arrow indicates this "ring" that I´m refering to, and yes, it has refractory in the same disposition as the picture. What you are suggesting makes sense to me.