Creep crack growth of seam-welded P22 and P91 pipes with artificial defects. Part I. Experimental study and post-test metallography

• Published in: International journal of pressure vessels and piping 2001-11, Vol.78 (11), p.819-826
• Main Authors: Le Mat Hamata, N, Shibli, I.A
• Format: Article
• Language: English
• Subjects: Applied sciences; Cavitations; Creep and fatigue crack growth; Exact sciences and technology; Fractures; Mechanical engineering. Machine design; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; P22; P91; Seam-welded pipe; Steel design; Steel tanks and pressure vessels; boiler manufacturing
• ISSN: 0308-0161; 1879-3541
• DOI: 10.1016/S0308-0161(01)00096-5

This paper describes the experimental work conducted on creep and fatigue crack growth behaviour in axially-notched, seam-welded pipes. The key objective of this work is to examine how the results from feature tests compare with standard laboratory specimen data using different European high temperature assessment methods, the final aim being to contribute towards the development and validation of a unified European procedure for estimating crack growth behaviour and remaining life of high temperature components. Within the context of this work, two steels P22 (2 1/4Cr1Mo) and P91 (9Cr1MoVNb) were studied at 565 and 625 °C, respectively. Two pipes were tested for each material; one pipe was subjected to a constant gas pressure (SP) and the other was tested under low cyclic pressure (CP) (10 −4 Hz). Each pipe contained three axially machined notches, one in the heat affected zone (HAZ) and two in the base metal. The direct current (DC) potential drop (PD) technique was successfully applied to monitor crack growth during the tests. In both steels, the defect situated in the HAZ exhibited a higher crack growth rate, confirming that the HAZ is more vulnerable to crack initiation and propagation than the parent metal. Post-test metallography analysis showed that creep cavitation damage is the main mechanism governing the crack propagation. In the case of the cyclic tests for which the selected frequency was close to, or slightly higher than, the frequencies encountered in high temperature plants, metallographic observations showed no noticeable effect of cyclic loading in terms of transgranular crack growth. The data analysis of the experimental data obtained in this work are presented in Part II of this paper [Creep Crack Growth of Seam-welded P22 and P91 Pipes with Artificial defects—Part II. Data analysis. Second International HIDA Conference, Advances in Defects Assessment in High Temperature Plant, MPA, Stuttgart, Germany, 4–6 October, 2000].