The integrity and the lifetime management of different engineering structures and structural elements is one of the important technical-economic problems nowadays. The purpose of the paper is to present the role of the external and internal reinforcing on the structural integrity of industrial and transporting steel pipelines, based on experimental investigations. External and internal reinforcement technologies were developed using carbon fibre reinforced polymer matrix composite (CFR PMC) and glass fibre reinforced polymer matrix composite (GFR PMC), respectively. Fatigue and burst tests were performed on large pipeline sections containing natural and artificial metal loss defects, seam and girth welds including weld defects ("NOT PASSED" quality). Burst tests were executed after fatigue tests, using 100.000 cycles. Different corrosion defects were tested as natural defects, and longitudinal and circumferential gouges as well as holes and through holes were investigated as artificial defects. Both unreinforced and reinforced pipeline sections were examined. The applicability of the hybrid structure (steel + polymer matrix composite) was demonstrated by means of the experimental results.