Abstract:
The repair welding of main steam pipelines, which involves the welding of new material onto
service-exposed material, are investigated. This paper investigates the literature and
experimental work surrounding this subject. The introduction provides a background to the
applicable welding technology. In section two the heat-affected zone is discussed with
emphasis on the residual stresses that develop in this zone. The mechanical properties of the
heat-affected zone are also investigated. This includes the tensile, toughness and hardness
properties as well as inspecting the relevant microstructures. The effect of post weld heat
treatment on these properties is also investigated. Section three investigates the
phenomenon of creep. Not only is this important due to the high temperatures at which these
pipelines operate, but creep is also associated with some failures of these weld during post
weld heat treatment. The creep properties of the heat-affected zone are investigated in detail
with the use of weld simulation. Sections four and five detail reasons for weld failure after
welding due to hydrogen and reheat cracking. Hydrogen cracking is investigated with the use
of slow strain rate tensile tests during cathodical charging the specimen with hydrogen. The
phenomenon of reheat cracking is investigated with the use of high temperature tensile tests
as well as a novel approach in which the stress relief of a welded joint is simulated while
measuring crack growth and stress relieved.
