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