Heat-affected zone of pipe welds

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Welding heat-affected zone: The area in the base material where changes in microstructure and mechanical properties occur as a result of heat exposure, without the material melting. 　　The microstructure and properties of the weld heat-affected zone essentially reflect the performance and quality of the welded joint. 　　The welding heat-affected zone is classified according to its microstructural characteristics into the fusion zone, the overheated zone, the normalized zone, and the incompletely recrystallized zone. Microstructural distribution in the heat-affected zone: (1) Fully quenched zone: During welding, the heat-affected zone is in a region above AC3; due to the high hardening tendency of this type of steel, a quenched microstructure (martensite) is obtained after welding. Near the weld area (corresponding to the overheated zone of low-carbon steel), severe grain growth occurs, resulting in coarse martensite, whereas the area corresponding to the normalized zone yields fine martensite. Depending on the cooling rate and wire energy, bainite may also form, resulting in a mixed microstructure coexisting with martensite. This zone belongs to the same type in terms of its microstructural characteristics (martensite), differing only in thickness; therefore, it is collectively referred to as the fully quenched zone. (2) Partially quenched zone: The base material is heated to the heat-affected zone within the range of AC1 to AC3; under rapid heating conditions, little ferrite dissolves into austenite, while pearlite, bainite, and sorbite in the heat-affected zone transform into austenite. During the subsequent rapid cooling, austenite transforms into martensite. The original ferrite remains unchanged and grows to varying degrees, eventually giving rise to a martensite-ferrite structure; hence it is referred to as the incomplete quenching zone. Sorbite and bainite may also appear when the carbon content and alloy element content are low, or when the cooling rate is slow. If the base metal is in a quenched and tempered state prior to welding, then in addition to the fully quenched and partially quenched zones mentioned above, the microstructure in the heat-affected zone may also undergo varying degrees of tempering, which is referred to as the tempering zone (the area below AC1). In summary, under the action of the welding heat cycle, the microstructural distribution in the heat-affected zone of metals is uneven. Severe grain coarsening occurred in the fusion zone and the overheated zone, which are the weak areas of the entire welded joint. For steel grades with high carbon content, numerous alloying elements, and a strong tendency to harden, martensite forms in the quenched structure, which reduces plasticity and toughness and thus makes cracks more likely to occur. They generally cannot overlap; otherwise, weld reinforcement bars are required to ensure strength. The properties of the heat-affected zone are related to the material of the welding material and the welding method; there is no fixed value!

I haven’t studied materials; these were only briefly covered in class. I learned it!

You can refer to the smallest pipe size for the minimum connection; this value is determined after taking into account the spacing between welds. These are engineering data. If you’re looking for theoretical data, there is information in the book on welding residual stresses. Different materials, different welding electrodes, different welding methods, and different heat impacts result in varying stress distribution ranges in copper.

Further inquiry: For pipe welds, what is the width of the heat-affected zone?

1 to 2 centimeters on either side of the weld edge

There are relevant data in ASME