The excessive weld reinforcement at the weld toe is prone to causing stress corrosion cracking. The stress concentration in butt joints is primarily induced by the weld reinforcement. Specifically, the stress at the weld toe, where the weld meets the base metal, is the highest.
The magnitude of the stress concentration factor depends on the weld reinforcement height (h), the angle (θ) at the weld toe, and the corner radius (r). As the weld reinforcement height (h) increases, the angle (θ) enlarges, and the radius (r) decreases, leading to an increase in the stress concentration factor.
A larger weld reinforcement height intensifies the stress concentration, which paradoxically reduces the strength of the welded joint. By removing excess weld reinforcement after welding, as long as it does not fall below the level of the parent material, stress concentration can be reduced, and in some cases, the strength of the welded joint can even be improved.
High external weld reinforcement is detrimental to corrosion protection. When epoxy resin-impregnated glass cloth is used for corrosion protection, a high external weld reinforcement can make it difficult to securely compress the weld toe. Additionally, a taller weld requires a thicker corrosion protection layer, as the thickness of the protective layer is measured from the peak of the external weld, thereby increasing the cost of corrosion protection.
During spiral submerged arc welding, an external weld with a "humpback" shape often occurs, further complicating the quality assurance of corrosion protection. Therefore, it is crucial to adjust the spatial position of the welding head and welding parameters to reduce or eliminate the "humpback" shape of the external weld.
High external weld reinforcement affects the pipe shape after hydrotesting and expanding. In the case of straight seam submerged arc welded pipes, during hydrotesting and expanding, the pipe is enclosed by two external molds, one on each side, whose dimensions match the expanding size of the steel pipe's inner cavity. Consequently, excessive weld reinforcement results in greater shear stress on the weld during expanding, causing the phenomenon of "small straight edges" on both sides of the weld.
However, experience has shown that when the external weld reinforcement is controlled at approximately 2mm, the "small straight edges" phenomenon does not occur during hydrotesting and expanding, preserving the pipe's shape. This is because with a smaller weld reinforcement height, the welded joint experiences less shear stress. As long as this shear stress remains within the elastic deformation range, the pipe will return to its original shape upon unloading due to elastic rebound.
High internal weld reinforcement increases energy loss in the transmission medium. When the inner surface of a submerged arc welded pipe used for transmission is not coated for corrosion protection, excessive internal weld reinforcement increases the friction resistance against the transmitted medium, resulting in higher energy consumption along the transmission pipeline.
