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Through Optimum Use and Innovation of Welding and Joining Technologies
Improving Global Quality of Life
most critical flaw type during fabrication most of such tests are targeted to define welding and respective
heat treatment procedures for crack avoidance. For this, numbers of test procedures have been developed
to assess the hot and cold cracking behaviour of welds. Significant progress has been achieved by the IIW to
compare the various procedures in Round Robins and to provide respective specifications, guidelines and
standards. Hence, numbers of heat treatment procedures for cold crack free welding of structural steels have
been specified and standardised. Design aspects have been taken less into account during establishment of
the respective test procedures.
As a major design aspect, an evaluation of
shrinkage restraint
of welds is gaining attention among the IIW
community now, because this parameter is significantly affecting the local and global stresses and strains in
a joint. Through the pioneering IIWwork, procedures developed in the seventies have provided quantitative
evaluation of the shrinkage restraint. These procedures have been improved in recent years and with the
advancements in numerical modelling, more insight has been gained on how the shrinkage restraint affects
the stresses and strains as well as respective cracking of joints.
In recent years, significant improvements have been made in the testing procedures of the welds for
determination of the tensile properties (local and global). The use of micro-scale specimens, for example,
micro-flat tensile specimens (0.5 mm thick and 2.0 mm wide) have been developed to establish the very
small weld volumes and HAZ gradients. The use of the micro-indentation technique has also been developed
to test extremely small zones of weld joints.
Fracture toughness
using Charpy-V or fracture mechanics (CTOD or J-integral) test methods have been well-
established for structural weldments. There exists ongoing discussions on the consequence and essence
of higher constraint specimens (deeply notched three point SENB specimen) versus weld (single edge
notched tension, SENT) specimens tested under tension (lower constraint) particularly for design and
qualification of the girth welds in pipes.
Testing under cyclic loading
for S-N behaviour is well established to be used in fabrication and design stages
as well as for design of welded structures. Furthermore, IIWhas developed unique
Fatigue Design Guidelines
including improvement techniques
over many years and nowadays used by industry for design of welded
components. With respect to fatigue crack propagation (FCP) test procedures, the community still uses
testing standards developed for base materials. Here, there exists need for further development of FCP
testing procedures taking into account the special features of the welds including narrow EB and laser beam
welds, dissimilar joints etc.
Fatigue testing, for instance, has been improved towards amore consistent evaluation of welds in comparison
to barely testing of base materials. Also, corrosion testing of welds is meanwhile carried out in more realistic
environments.
Significant progress has been made in testing of
component-like welded specimens
and/or
complex
welded components
under different loading conditions (uni-axial or multi-axial) as well as under the
environmental conditions (e.g corrosive or sub-zero temperatures). These tests (in limited number) are
usually accompanied with numerical simulations to predict or verify predictions of service performance.
Obviously these tests contain the effects of welding residual stresses, as exist under the testing conditions
of interest. Nevertheless, suitable test procedures have to be developed to simulate more complex, but
respectively realistic conditions to gain more insight into the service behaviour of welded components in
combination with modelling efforts.
As further perspectives, sensorics and micro-electronics will increasingly be applied to both, materials
related testing and, in particular, to the testing of welded/joined components. Also on-line monitoring and
in-situ investigations (including structural health monitoring, SHM) during fabrication and service of welded
structures will gain importance.
4
Needs and challenges in welding and joining technologies
