Evaluation of Methods to Predict Safe Welding Conditions and Maximum HAZ Hardness in Steel Welding

Abstract

During the last ten years new structural steels of improved weldability have been introduced. In particular, structural steels for the fabrication of offshore structures have been greatly improved in this respect throughout this period. These steels have lean chemical compositions which are generally outside the range for which the existing HAZ hardness criteria and the International Institute of Welding carbon equivalent (CEIIW) formula were originally developed. This paper presents the results from investigations of the weldability of three normalised (Re min 350 MPa) and three quenched and tempered (Re min 500 MPa) offshore structural steels. Weldability testing was conducted to study the relative performance of the different steels and to obtain a comparison between the capability of the different methods to predict safe welding conditions to avoid cold cracking in steel welding. It has become a widespread practice in welding high-strength steels to incorporate maximum HAZ hardness restrictions in fabrication specifications, particularly so in the offshore industry. Maximum HAZ hardness restrictions are often a point of contention between fabricators and their clients due to the difficulties often experienced in meeting these hardness requirements. Problems meeting maximum HAZ hardness requirements have been encountered for applications where maximum hardness HRC 22 or Vickers HV10 260 have been imposed for materials exposed to sour service in oil and gas production, processing and transportation. Many attempts have been made to develop empirical formulas for the estimation of maximum HAZ hardnesses. This paper presents some of the more successful approaches proposed to date and compares their performance.