11149 Damaged Long Seam Weld on an Outlet Elbow outside Hot Box of an Ethane Cracking Furnace

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Product Number: 51300-11149-SG

ISBN: 2011 11149 CP

Author: Jeffrey Xie, Marek Crawford, David Eisenhawer, Chris Sturdy, Mark Maxwell, Lorrie Davies and Les Ben

Publication Date: 2011

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A long seam weld located on the inside radius of a 90° elbow coming out of a hotbox of an ethane cracking furnace, was found to be damaged at the end of 2008. The damage was in the form of cavities. Metal dusting and erosion were determined to be the root causes for the damage. Erosion played an important role in forming crevices for coke deposit, initiating carburization, and subsequently metal dusting.

The damage was restricted totally to the long seam weld. There was no visible damage found on two nearby circumferential welds. The major difference in these welds was the material used for the root passes. The root pass of the long seam weld was made using alloy AWS ERNiCr-3, and that of the circumferential weld was made using alloy AWS ENiCrCoMo-1. Particles enriched with molybdenum (Mo) and Silicon (Si) were found accumulated at the weld surface. These particles formed a protective layer to resist erosion and carburization, resulting in additional protection for the circumferential weld. The root pass of the long seam weld, however, was potentially less protective due to the lower chromium content and lack of a Mo/Si-rich layer underneath the surface oxides. It is thus recommended that the root pass of the long seam weld be replaced with alloy AWS ENiCrCoMo-1 or other filler metals with higher chromium contents for better resistance to process environment.

Key words: Metal dusting, carburization, erosion, weld, oxides, alloy AWS ERNiCr-3, alloy AWS ENiCrCoMo-1, and alloy UNS N08810