Reducing welding repair requirements in refinery pressure vessel manufacturing: a case study applying six sigma principles

Abstract

High welding intensity is an integral part of the refinery pressure vessel manufacturing process. Weld defects are also responsible for a substantial part of the rework requirements, waste and operating costs associated with such manufacturing. Seeking ways to reduce welding defects and improve the efficiency of the manufacturing process is therefore critical for profitability and fulfills customer expectations of product reliability. A problem-solving project applying six sigma principles, and specifically its define, measure, analysis, improve and control methodology, successfully identified, quantified and reduced weld defects in pressure vessel manufacture for the Machine Sazi Arak Company leading to ongoing process improvement gains. Failure modes and effect analysis and customized experiments were able to quantify the impacts of identified root causes on the slag inclusion, lack of fusion and porosity weld defects. This lead to improvement solutions being successfully tested and implemented. These improvement initiatives significantly reduced the average number of the welding repairs required, increased the sigma level of weld defects by up to 19% reduced welding process costs by up to 350% and increased process yield by 1.12%. Consequently, the profitability and efficiency of pressure vessel manufacture was much improved by adopting the six-sigma problem-solving approach.