Improving Global Quality of Life
Improving Global Quality of Life
Improving Global Quality of Life
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9 Needs and challenges <strong>of</strong> major industry sectors for future applications<br />
New methods <strong>of</strong> repair and maintenance including the use <strong>of</strong> composites.<br />
In-line inspection <strong>of</strong> butt fusion welded plastic pipe.<br />
Mechanised welding <strong>of</strong> external and internal joints on mainstream pipelines.<br />
High-pressure water-jet cutting <strong>of</strong> damaged concrete support structures for low cost maintenance<br />
<strong>of</strong> in-service pipelines.<br />
High integrity mechanised welding <strong>of</strong> titanium.<br />
9.12.1 Hot topics<br />
The specific aspects <strong>of</strong> challenges where welding and joining technology transfers are needed and<br />
contribute to meeting the national objectives include the following:<br />
Urgent need for a country to upgrade its water catchment, storage, treatment and distribution and<br />
waste water infrastructure in both urban and rural applications.<br />
Minimisation <strong>of</strong> resource wastage and the risks <strong>of</strong> serious health and supply breakdown due to<br />
failing pipes/distribution.<br />
Maintenance <strong>of</strong> aging infrastructure.<br />
9.13 Advanced steels sector<br />
The use <strong>of</strong> advanced steels with enhanced properties can contribute to the improvement <strong>of</strong> ordinary life in<br />
many aspects. Welding <strong>of</strong> advanced steels in similar and dissimilar configurations poses challenges, however.<br />
For example, High Strength Low Alloy (HSLA) steels with ultimate tensile strengths not less than 780 MPa<br />
were developed by many steel companies, but their welding is faced with the following problems:<br />
Lack <strong>of</strong> knowledge about the metallurgical factors <strong>of</strong> the weld metal necessary to obtain required<br />
mechanical properties.<br />
Requirement <strong>of</strong> preheat at temperatures rising with the base metal strength.<br />
Welding residual stress that increases with the base metal strength and limits the tolerable ultimate<br />
and fatigue strength <strong>of</strong> the weld to levels much lower than the base metal.<br />
9.13.1 Metallurgical challenges<br />
With respect to the metallurgical factor, the acicular ferrite, which forms through γ → α transformation<br />
intragranularly nucleated at oxide inclusions, is generally accepted to be a desirable one with sufficient<br />
ultimate strength and toughness for the weld metal for HSLA steels <strong>of</strong> 580 MPa class or less. The acicular<br />
ferrite, however, is thought to be insufficient to bear the mechanical load required for the steel <strong>of</strong> more<br />
than 780 MPa classes, and so a microstructure harder than the ferrite, like a bainite and martensite (B+M)<br />
microstructure, is expected to be suitable for the weld metal <strong>of</strong> the steel with higher strength.<br />
An important difference between the weld metals <strong>of</strong> acicular ferrite and B+M microstructure is the effect<br />
<strong>of</strong> oxide inclusion that is indispensable for the formation <strong>of</strong> the acicular ferrite as a nucleation site. For the<br />
B+M structure, however, the oxide inclusion is unnecessary for their formation, and has significantly harmful<br />
effects on the toughness at volume fractions introduced during conventional arc welding processes except<br />
for tungsten inert gas (TIG) welding and metal inert gas (MIG) welding. Although TIG and MIG welding can<br />
produce weld metals with much lower oxide contents, they are difficult to carry out at high heat inputs, and<br />
so inferior in the welding productivity to the other arc welding processes.<br />
Through Optimum Use and Innovation <strong>of</strong> Welding and Joining Technologies<br />
<strong>Improving</strong> <strong>Global</strong> <strong>Quality</strong> <strong>of</strong> <strong>Life</strong><br />
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