Adjusting the Boiler Code

Abstract

Technological advances have made it possible to reduce the material design factor in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Today solid-state circuitry is the only power source used in welding equipment. The use of solid-state circuitry has brought a great deal of stability to the electrical characteristics of the arc, and this in turn has resulted in weldments with considerably fewer imperfections. The US government sponsored a study to determine the causes of the failures and to evaluate the metallurgical and other factors that contributed to the fractures. This project studied samples from more than 100 ships, in which serious failures had occurred. This and other concurrent studies around the world led to an understanding of the role of notch toughness in preventing failures in pressure boundary components. The conservativeness of Section I and Section VIII, Division 1, continues to be significant. The change from 4 to 3.5 in the material design factor will not compromise safety. The denominator for determining an allowable stress based on yield strength remains the same, 1.5. The probability of failure of a pressure-containing component due to an overstress condition is small. The change from 4 to 3.5 has had very little impact on that conservative material design factor.