Weldability and weld joint failures

S&than& Vol.20, Part 1, February 1995,pp. 213 232.@ Printed in India. Weldability and weld joint failures M N CHANDRASEKHARA1AH Welding Research Institute, Bharat Heavy Electricals Ltd, Tiruchirappalli 620 014, India Abstract. Welding plays a prominent role in the fabrication and erection of structures and components in the industry. Weld failures when they do occur, either during fabrication or service, involve considerable rework, apart from production, time and material losses. Hence, it is essential to adopt appropriate welding procedures depending on the material, weld configuration and the service requirement. In addition, the weldability of the material should be established with adequate laboratory tests in order to minimise the tendency towards hot and cold cracking susceptibilities. The mechanisms of such cracking and the tests to be undertaken to evaluate the cracking susceptibility are enumerated in this paper along with a brief report on weld failures and criteria to be adopted for their repair. Keywords. Weld failures; weld repair; weldability; cold cracking; hot cracking. 1. Introduction Weiding plays a significant role in the fabrication, erection and commissioning of plants and machinery for power, petroleum, chemical, steel and other industrial sectors. With the improvement in steel-making technology and the availability of better and cleaner steel grades with higher strength-to-weight ratios, the capacity, efficiency and availability of plants and machinery are continuously increasing. The advent of better design capabilities+ using complex structural analysis with finite element and other methods, has enabled optimisation of section thickness with reduced factor of safety and considerable savings in material and fabrication costs. Manual metal arc welding is being replaced by better, automated and sophisticated welding technologies which reduce the fabrication and erection time considerably and also give better and consistent quality of welds. The effect of these technological advances is that the pressure parts and other components are now exposed to severe temperature, pressure and environmental conditions for prolonged periods of time which may, sometimes, lead to unforeseen and catastrophic failures. The weldments and heat affected zones (HAZ), which are structurally non-integral with the base metal, are more prone to such failures. Apart from the cost and time required for the weld repair of such components, the plant outage leads to considerable financial los:~es. Hence, it is important to understand the factors responsible for such 213

Weldability and weld joint failures

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weld failures

weld repair

weldability

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