Carburization of A-106B Tubes

[dsphillips]

We have a lean oil heating furnace with A-106b tubes. The approximate tube temperature (surface) is 750F. We have a haz-op item on this that says we need to verify that the tubes are not susceptible to carburization. Can someone lead me to a reference chart, or some other text to help me verify this. Thanks.

 

[AEF]

A-106 material is prone to graphitization when exposed to temps > 800F for long periods of time (ASME B31.3 Notes for App. A). As for carburization, I wouldn't expect much at temperatures below 800F.

 

[rustbuster1]

AEF has it!
Carburized surfaces have diffused carbon enrichment at the surface which makes the surface a higher carbon alloy and allows local hardening. This would not occur at 750F.

AEF surmises you mean "graphitization", which is a slow process converting carbon in the pearlite from an iron carbide to the graphitic form of carbon and weakening the steel. This also is so slow at 750F it is a non-issue. You can test for it metallurgically with in-field metallography/replication or by destructive testing of removed samples - welds are usually selected. The main message you should sell is that this normally is not necessary at 750F