To consistently achieve low hardnesses in an in-service weld experiencing high cooling with high carbon equivalent is difficult, and even more difficult to achieve when trying to target sour service micro-structures. In-service welding relies on one of two methods to achieve appropriate weld and heat-affected-zone (HAZ) properties in carbon steel. The two main methods are temper-bead welding and heat input technique. This paper explores the temper-bead technique including showing the positive and negative effects of overlapping heat-affected zones as it relates to course-grained and fined-grained heat affected zones. Other work regarding tempering for in-service applications has been completed. Temper-bead welding depends on several variables including amperage ratio, travel speed, electrode diameter, weld-build-up thickness, grinding thickness and preheat.
A series of trials were completed with various welding variables including amperage, travel speed, electrode diameter, preheat, cooling condition, carbon equivalent to demonstrate reduction in HAZ hardness, to the extent that is required to meet 250 HV sour service hardness under severe cooling and high carbon materials. Each trial underwent hardness testing, specifically at the toe of the weld, with 5 hardness spots in accordance with API 1104 Annex B. The images were also analyzed to show heat affected zone depth and the overlap of the coarse-grained heat affected zone by the fine-grained heat affected zone through re-austenization.
The research demonstrates the importance of preheat and specifically the importance of properly overlapping the course-grained (CG) HAZ with a fined-grained (FG) HAZ to produce the required hardness for in-service welding. The paper explores the difference induction preheat and no-preheat has on temper bead welding during simulated in-service welding conditions, and the effect of amperage to affect the penetration geometry of the weld.