Reference no: EM132366870 , Length: word count:2250

Introduction to Materials Welding and Joining Assignment-

QUESTION 1: Dragline excavators are used in the opencast mining of coal to remove and stack topsoil. The boom of such an excavator consists of long tubular carbon steel pipes (with wall thicknesses of approximately 20 mm for the main members and 10 mm for the cross members) welded to form a lattice structure (see Figure 1 below). These welds are prone to fatigue failure due to flexing of the boom during service and require frequent repair welding to ensure uninterrupted production. Major repairs are performed every three months during a scheduled outage during which the boom is lowered to the ground (as shown in Figure 2), allowing easy access to the cracks for rewelding. These major repairs cannot be performed more frequently due to the high production losses experienced and the difficult and time consuming rigging process required to lift the boom. Any cracks detected during the frequent nondestructive inspections between major overhaul operations are ground out and removed completely, before being rewelded using GTAW (for the root pass) and MMAW (to fill the remaining gap) with E7018 electrodes. Repairs are usually done at night (to reduce production losses) and in some cases require the welders to be suspended in harnasses up to 60 m above ground. Wind is a major problem during welding. Repair welds performed under these difficult conditions often last only 2 weeks. You are appointed as a consultant to review the current welding procedure and recommend changes that will extend the life of the welds. Answer the following questions:

1.1 Review the current repair welding procedure (i.e. GTAW root, MMAW filler passes with E7018 electrodes) and discuss whether this procedure may contribute to the rapid failure of the repair welds.

1.2 Suggest an alternative process that will address some or all of these problems and extend the life of the welds. Motivate your answer.

QUESTION 2: Fusion welding often causes distortion of the component being welded. Distortion is undesirable and can have an adverse effect on the ability of the component to serve its intended purpose. Prepare a short literature review article (maximum of 2000 words) addressing the current theories related to the following aspects of welding and distortion:

How does distortion develop during fusion welding of metallic components?

What forms of distortion are found in welded components?

What adverse effects can distortion have on the performance of a welded component?

How can distortion be avoided during welding or rectified after completion of the weld?

Format and referencing - You are expected to review and cite relevant reference material from a range of credible sources including reference books, peer reviewed journals and online resources. Please refer to the subject outline for more information on referencing systems.

Note - Words Count for Ques1: 750 and Words Count for Ques2: 1500. Please add the references at the bottom.