Stress Corrosion Cracking of 316 Stainless Steel Pipe-Flange Joint in a Continuous Catalyst Reformer (CCR)

Monday, September 13, 2021: 11:40 AM
241 (America's Center)
Dr. Suresh Divi , Stress Engineering Services, Houston, TX
Continuous Catalytic Reforming (CCR) is a chemical process that converts petroleum refinery naphtha distilled from low-octane oil into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline.

A 3-inch stainless steel pipe-flange joint in a continuous catalyst reformer (CCR) unit experienced a leak due to initiation of pinholes next to the weld section. The pipe carried hot re-generation gas and it operated over a wide temperature regime.

The inside surface areas that were examined appear to have corroded throughout the length of the 316 stainless steel pipe and flange. Chloride was consistently detected in the corrosion product, near and away from weld locations.

Pitting corrosion of the ID surface and thermal fluctuations acted as the precursor to form a stress concentration region. Multiple cracks emanating at the ID appear broad, similar to thermal fatigue; however, the absence of oxide filled cracks and the presence of branched crack tips support the SCC mechanism with possible contribution from thermal fluctuations.

Key words: Continuous Catalytic reforming (CCR), Stress Corrosion Cracking, 316 Stainless Steel