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

528

3

(Common outlet on Fig. 2). The system was isolated with glass wool and aluminum foils of 45cm thickness. Consequently, the installation, and especially the mixing area, is subjected unevenly to high temperature and pressure of two different pressure and temperature steams.

Fig. 2. The failed area of the tee fitting just after removed from the unit.

Chemical analysis was performed on two areas; on mixing area, with high cracks concentration (area No 1), and on the lower temperature inlet steam’s side (area No 2). As shown on Table 1, the chemical analysis revealed that the tee fitting was manufactured from Incoloy 800H, and the material was in compliance with standards (ASTM B407, 1996).

Table 1. Chemical composition of the steel compared with the standard composition [% p.wt.].

Chemical elements Area No 1 Area No 2

C

Cr

Ni

Co

Ti

Si

Mn

Al

Cu

S

0.061 0.063 0.05- 0.10

19.32 19.22 19.0 23.0

31.32 31.33

0.057 0.056

0.428 0.428 0.15 0.60

0.412 0.409

0.78 0.77 Max 0,15

0.453 0.453 0.15 0.60

0.129 0.128

0.0005 0.0005

Max 2.00

Max 1.00

Max 0.75

Max 0.015

Incoloy 800H

30-35

The Incoloy 800H is a nickel-iron-chromium alloy having high chemical and mechanical properties. It is a common piping material, designed to maintain high-temperature strength and to resist to oxidation, corrosion and carburization (Stainalloy 2019). It is usually selected for manufacturing of furnaces’ components and equipment, petrochemical furnace cracker tubes, pigtails and headers, and sheathing for electrical heating elements (Van der Geer and al. 2010). Consequently, the particular pipe is a high-cost engineering part manufactured from a material suitable for the specific applications. The visual inspection on the external area revealed a circumferential crack on the welding zone, between the reinforcing pad and the tee’s pipeline, on the inlet side (high temperature steam). The crack covers more than 50% of the circumference (arrows on Figs. 3a), and also propagated by 50 mm in one of the two longitudinal welds (arrows on Fig. 3b). Furthermore, cracks were developed on the welding zone between process pipes (Fig. 3c).

Fig. 3. (a) Images showing the circumferential crack on the welding area between reinforcing pad and the rest pipeline.