PSI - Issue 77

Jan Kec et al. / Procedia Structural Integrity 77 (2026) 264–271

266

A Elongation Δ K Stress intensity factor range F Force LLD Load line displacement

2. Investigated Material and Experimental Methods A pipe segment of X52NE hot-rolled steel with an outer diameter of 323.9 mm, wall thickness of 11 mm, and length of 1,000 mm was used for sample preparation. The pipe featured a longitudinal high-frequency welded (HFW) seam. Chemical composition analysis was conducted using an optical emission spectrometer (SPECTROMAXx), with results matching ISO 3183 requirements (Table 1). The base material exhibited a fine-grained ferrite-pearlite microstructure (avg. grain size: 9.29 µm, Fig. 1a). In the area surrounding the weld line, it can be observed that the microstructure is aligned in the direction of the slag formation. The 100 µm-wide weld centerline was defect-free with partial decarburization (Fig. 1b). Mechanical properties (Table 2) confirmed compliance with ISO 3183, with the weld centerline showing higher tensile strength (610 MPa) and CVN impact energy (123 J at 0°C) compared to the base material (570 MPa, 91 J).

Table 1. Chemical composition of investigated X52NE pipeline steel

Element content [wt. %]

C

Si

Mn

V Nb

Ti

P

S

Base material

0.17 0.19 1.36 0.01 0.05 0.02 0.014 0.007

Required chemical composition of X52NE steel according to ISO 3183

max. 0.22

max. 0.45

max. 1.40

max. 0.01

max. 0.05

max. 0.04

max. 0.025

max. 0.015

Table 2 Mechanical properties of investigated X52NE pipeline steel Direction of specimens

CVN impact energy at 0°C [J]

R m [MPa]

A [%]

R t0.5 [MPa]

Base material Weld centre line

437

570 26.2

91

-

610

-

123

360 - 510

460 - 760

min. 20

Required mechanical properties of X52NE steel according to ISO 3183

min. 27

(a)

(b)

Fig. 1. Microstructure of (a) base metal; (b) weld centerline.