Impact of Welding Defects on Integrity of Equipment & Piping

Introduction

Welding is one of the most important techniques in the fabrication industries to join metals in different geometries and sizes with cost-effective and reliable assembly. There are several types of welding processes used in the petrochemical industry that have been around for many decades and new methods developed in recent years. Basically, these processes vary in setup, essential variables and non-essential variables, such as shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW), etc. Each welding process has characteristics that affect its quality performance and the soundness of the weld. For example, a weld acceptable for one application, such as for a tank, may not meet the acceptance criteria for pressure vessels per applicable international codes. Welding imperfections such as cracks, porosity, lack of fusion, incomplete penetration, and spatter could be due to various causes, such as poor workmanship, design issues, incorrect material, improper weld procedure specifications, and/or an unfavorable environment. The impact of each defect varies from acceptable to not acceptable, and must be either repaired or cut-out.  

Therefore, it is important to ensure the quality and reliability of welds in equipment prior to placing it into service using nondestructive testing (NDT) methods and ensuring compliance with the requirements of international standards. Moreover, piping systems should be hydrotested to ensure the integrity and strength of the entire system. Some welding defects, however, can only be discovered while the facility is in operation, such as crack initiation. These defects will require engineering assessment, such as Fitness-for-Service, to determine the proper remedial action.