Ethylene Furnace tubes contamination 1

[Cormet]

Colleagues,

Alloy is 35Cr45Ni (no ASTM spec to reference).
1. Furnaces are being erected and it was noticed that some of the tubes have multiple rust spots, typically these results from carbon steel contamination.
I'd like to hear your expert opinions on expected damage mechanisms if carbon contamination is not removed. We think that these rust spots will likely carburized and some carbon will tend to form carbides with chromium. These chromium carbides will affect high temp properties of alloy (ex: creep, carburization resistance).
2. Second issue that was noticed in regards to galvanized scaffolding being used. We believe that if galvanized scaffolding comes in contact with this alloy it will cause LME due to zinc contamination.
is there a field test that ca be used to detect Zn on this alloy?
Regards,
Cormet

















lmE

 

[EdStainless]

The are cast, correct?
The rust spots don't bother me. This will be very superficial.
The Zn could be another thing.
I don't know of an easy detection method.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[Cormet]

EdStainless
Yes, these are centrifugally cast tubes.

 

[Dhurjati Sen]

Dear Cormet,

These tubes are also used in Hydrogen Generation Unit reformer furnaces.

The rust spots are of course carbon contamination. They often form due to poor storage practices in the warehouse.

Zinc contamination is also not an issue, as while performing H scans or inspection of pigtails etc. scaffolding are erected which are either galvanized or painted.

Mid-wall cracking is the common mode of failure of these tubes.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[cap1a79]

I) At first, check if the rust is composed of "carbon" and where the carbon came from?

ii) If they are new tubes, then why the rust was found? Is it poor storage? Any cleaning(for new tube) applied?

Note that generally the rust on carbon steel is iron oxide(ex. Fe2O3) whose color is earthy (ex., red, brown, black.) Carbide phase (ex., Fe3C) is decomposed in case the temperature is elevated. At least, we can say that it is not decomposed or precipitated and moved to other steel in the air.

Regarding LME, note that the mechanism is applicable when "molten zinc" (such as fire case) contacts with "300 series SS". If you ensure the molten zinc does not contact with 300 series SS, the mechanism you have concerned will not be an issue.

Lee SiHyoung,
WorleyParsons Oman Engineering,

 

[EdStainless]

The reason that Zn does not usually cause issues is that the start up is in air, and any traces of Zn will oxidize long before you reach the melting point. This could be an issue if you were in a neutral or reducing environment the first time they were heated

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube