Improving Global Quality of Life
Improving Global Quality of Life
Improving Global Quality of Life
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An example <strong>of</strong> the value <strong>of</strong> welding to a small economy is shown by this example from New Zealand (NZ)<br />
(population 4.4 million) undertaken by an industry-based research organisation the NZ Heavy Engineering<br />
Research Association (HERA).<br />
The study has produced some interesting results, such as:<br />
An estimated 6,500 people’s work involves welding, and a further 800 people are involved as<br />
welding supervisors, engineers, or inspectors.<br />
The value added <strong>of</strong> welding and joining technology in 2007 was estimated as NZ$813 million.<br />
In 2008, around 4,000 tonnes <strong>of</strong> welding consumables (imported and locally manufactured for the<br />
local market) with an estimated total value <strong>of</strong> NZ$15 million was available on the NZ market.<br />
3.5 Failures <strong>of</strong> welded structures<br />
Structural performance <strong>of</strong> the welded components strongly depends on the local joint quality. The<br />
welded structures are <strong>of</strong>ten fabricated to satisfy conflicting requirements (low cost and weight, long life<br />
and performance, limits <strong>of</strong> the technology) <strong>of</strong> material/design/technology. Additionally, welded or joined<br />
components inherently contain micro- and macro heterogeneities and stresses at the joint areas, which may<br />
contribute to the failures <strong>of</strong> the components. Prevention <strong>of</strong> failures and ensuring long and safe life <strong>of</strong> welded<br />
structures (such as <strong>of</strong>fshore platforms, pipelines, steel constructions, bridges etc.) also depends on the<br />
effectiveness <strong>of</strong> the corrosion protection. Fatigue is a serious problem (see Figure 3.3) for welded structures<br />
subjected to repeated or fluctuating loading in service. Advanced design and flaw assessment guidelines<br />
are now available, however, to prevent failure <strong>of</strong> a component and ensure structural safety. Regarding the<br />
corrosion resistance <strong>of</strong> welded structures, the current guidelines and standards are predominantly related<br />
to base materials. This provides future challenges and tasks to adopt the respective practices to welded<br />
components. Furthermore, there is a need to describe the effects <strong>of</strong> the various weld microstructures and<br />
residual stresses on the resistance <strong>of</strong> components against corrosion damage and cracking.<br />
Figure 3.3 Fatigue crack propagation<br />
in laser welded aerospace Al-alloy<br />
(Reproduced courtesy: GKSS, M. Kocak)<br />
Failures <strong>of</strong> the welded components are usually due to the deterioration <strong>of</strong> the material/weld properties<br />
(development <strong>of</strong> a crack or local damage under fatigue, creep, corrosion or their combinations etc.) and/<br />
or an increase in loading and/or localised external damage and/or change in function <strong>of</strong> the component.<br />
A satisfactory life-cycle <strong>of</strong> the welded structures requires a correct assessment <strong>of</strong> the stress levels and cycles<br />
as well as correct determination <strong>of</strong> the weld joint local properties. When weld joint failures are experienced<br />
in service (due to fatigue), it is <strong>of</strong>ten in cases where the acting stress levels (and overloads) are not known<br />
or have increased during the service life by far more than was foreseen at the design and fabrication stages.<br />
Strength mismatch (see Figure 3.4) between weld deposit and base metal as well as weld width (2H) play<br />
significant roles on crack tip deformation and failure behaviour <strong>of</strong> welds with respect to residual strength.<br />
This feature has now been taken into account in new codes and standards dealing with structural integrity<br />
assessment <strong>of</strong> welded structures.<br />
14 <strong>Improving</strong> <strong>Global</strong> <strong>Quality</strong> <strong>of</strong> <strong>Life</strong> Through Optimum Use and Innovation <strong>of</strong> Welding and Joining Technologies