Masters Theses

Date of Award

5-2015

Degree Type

Thesis

Degree Name

Master of Science

Major

Materials Science and Engineering

Major Professor

Carl D. Lundin

Committee Members

Carl J. McHargue, Hahn Choo

Abstract

Five materials encompassing various grades of carbon steel were received from retired and ex-service petroleum refinery equipment for root-cause evaluation of High Temperature Hydrogen Attack (HTHA) damage at UTK. These materials were submitted by three contributors: Irving Oil Refinery (IOR #1110-2), Valero (#67 & #1252134), and Phillips 66 (#555-S1 & #555-S2) on behalf of American Petroleum Institute (API). These materials originated from various flange-to-pipe welded components that were exposed in hydrogen pressure environment at elevated temperatures (> 640°F and >70 psia).

A singular crack originating at the flange inside surface just outside of the visible HAZ was observed in IOR #1110-2 and Valero #67, respectively. Cracking in IOR #1110-2 was 1/4” long in the circumferential direction and ~3/8” deep (3/4 of the flange wall) in the sample received at UTK. A singular crack 5/8” long in the flange circumferential direction and 3/4 deep was found only in one quadrant in the flange base metal just outside of the visible HAZ. However, the cracks in these components (IOR #1110-2 and Valero #67) were different from traditionally accepted HTHA morphology, i.e. no decarburization, no residual methane, and no evidence of cavitation were observed adjacent to crack areas. Cracking in these two components showed a mixture of intergranular and transgranular cracking morphology. No evidence of cracking or microstructural damage was observed in Valero #1252134.

The Phillips 66 component, #555-S1 showed the evidence of the beginning stage of HTHA damage with grain boundary microfissures in the flange base metal just outside of the visible heat-affected zone (HAZ); no apparent decarburization was observed adjacent to microfissures. The presence of methane cavities were observed along pearlite/ferrite and ferrite/ferrite boundaries. A residual methane content of 28 ppm was measured in the damaged region of P66 #555-S1 (from the most damaged area). No evidence of fissuring or decarburization was observed in the second component received from P66 #555-S2. The results showed two of the components exhibited nontraditional form of HTHA damage, two components did not exhibit any damage, and one component from Phillips 66 exhibited traditional HTHA damage.

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