Abstract
It is well known in the hot rolled steel making business that nonmetallic inclusions play critical role in defining steel performance. The objective of this paper is to study laminations that were detected via Phased Array UT system in X60MS Class-C High Frequency Welded Pipe intended for offshore application. The linear intermittent laminations appear along the pipe and adjacent to the weld seam from both sides at a width of 30 to 40 mm with various depths. Technical review was carried out on 5 available pipes, pertaining to the same heat of the original pipe identified earlier with lamination, through model experiments; both on the laboratory and on the industrial scale. At the beginning, depth and distribution of detected laminations were analyzed by manual UT mapping using normal beam probe. Metallurgical analysis via Energy Dispersive X-ray (EDX) was carried out on three samples to determine the chemical composition as well as the morphology of the lamination. The type of inclusion which turned out to be type B (Alumina-Al2O3) inclusion was identified by evaluating EDX results using Method A per ASTM E45. As it is a pure material based incident, failure analysis was carried out by the steel maker to identify the associated root causes from process control prospective and the appropriate preventive measures to avoid reoccurrence. Eventually, the applied quality control measures during manufacturing process of HFW pipes, represented in the deployment of UT systems, were reviewed to identify the reason behind missing such important defect before pipes are being shipped to the client.
