An Engineer’s Guide to Nondestructive Weld Examination

Abstract

The application of nondestructive examination (NDE) for welding of steel pipe and steel cylinders is a topic that requires forethought and knowledge. Specifically, when to use a certain NDE method, how to determine the frequency of examination, and the acceptance criteria to apply. NDE methods often vary from project to project, and understanding each method will help the engineer determine which process or combination of processes to use for a specific project. These quality assurance checks are useful for confirming weld quality in the final product before it is put into service. A weld that looks great on the outside is often seen as high quality and this is hopefully the case. Unfortunately, surface appearance alone cannot be used to verify good workmanship or internal weld quality. Many pipeline owners operate on limited budgets and need systems that can perform for many years with minimal or no maintenance. Water main and other pipeline ruptures almost always make front page news, which is why following good design practices in combination with the use of secondary checks to verify fabrication quality are important. Most pipe fabrication standards require some NDE, typically in the form of hydrostatic testing and visual inspection. These tests are useful for locating leaks and surface defects, but they will not confirm that a weld has complete joint penetration or that individual weld beads are free from objectionable defects. Additional forms of NDE must be specified by the engineer and are often needed for critical applications and projects that involve field welding to confirm weld quality. This paper will provide an overview of Visual Inspection responsibilities and additional NDE methods specified by engineers. A description of what each NDE method is capable of detecting, its benefits and limitations is also included. Specific NDE methods that will be discussed include: • Radiographic Testing (RT) • Ultrasonic Testing (UT) • Magnetic Particle Testing (MT) • Liquid Penetrant Testing (PT) VISUAL INSPECTION RESPONSIBILITIES The first step is to understand fabricator and contractor responsibilities for welding inspection and quality control. Visual inspection begins at the shop with an examination of incoming materials, checks on joint preparation, root openings, and assessing the quality of alignment and cleanliness. Most pipe fabrication shops adhere Pipelines 2015 250