PSI - Issue 17

C. Medrea et al. / Procedia Structural Integrity 17 (2019) 526–531 C. Medrea, E. Pappa, D.G. Papageorgiou, C. Stergiou / Structural Integrity Procedia 00 (2019) 000 – 000

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boiling point of their constituents (Vollhardt and Schore 2011).

Fig. 1. Schematic illustration of petroleum distillation; (a) Petroleum distillation tower, (b)Petroleum fractions.

From environmental and economic reasons, the process includes the sulfur recovery. Recent legislation imposes to recover at least 99% of the sulfur in refinery gas. The process requires specific steps (sulfur recovery, thermal incineration, sulfur degasification), and is implemented in particular desulphurization units, named Claus type (Gary and Handwerk, 2001). The paper analyses the cracks propagated in a tee pipe, part of a desulphurization unit of a local refinery. The study of various types of failures in the field delivers practical solutions to the specific problems and in some cases result to quality improvement. The section is a part of a larger scale industrial installation and was removed with a saw. The segment required further sectioning in order to be transported for analysis and was furthermore sectioned into three pieces, using a pneumatic hand cutting tool. Recorded history was collected regarding fitting, use, maintenance and manufacturing and the failed part was preliminary examined (Pappa and al. 2018). Chemical analysis was performed using an optical emission spectrometer (OES) and the material used for the fitting manufacturing was verified. The fragments were visually inspected, and macroscopically examined, as received. A photographic archive was created to underline the most significant features. A camera with micro and macro photo-shooting ability was used. The pieces were cleaned by sandblasting in order to remove any superficial signs of hard deposits and dust. Cracks were investigated using liquid penetrants testing. Samples of further sections were selected for destructive testing. Areas where defects detected were macro etched and visually inspected. An equal tee fitting was installed on a desulfurization unit type Claus, part of a local refinery plant. Systematic failures were detected on this part. The installation was manufactured from the maintenance department of the refinery. It is composed from two pipes (thickness 1in. and 6 in. diameter respectively) of Incoloy 800H, with a reinforcing pad welded together using metal wire of ER NiCrNb 3221. The fitting has on the bottom side of the reinforcing pad a leakage hole sealed with a bolt, in order to permit the internal leakage observation of the in-service tee fitting. Superheated inlet steam at 650 o C to 700 o C, and under 13bar pressure is inserted in the pipe from one side (Higher temperature inlet on Fig. 2), and lower temperature inlet steam, between 290 o C and 320 o C, but in higher pressure, of 25bar is inserted from the other side (Lower temperature inlet on Fig. 2). The mixed steam with temperature between 465 o C and 535 o C and pressure between 10bar and 12bar comes out of a common exit 2. Experimental 3. Results and Discussions