technical case study
Where: ΔW is the estimated shrinkage across the joint A is the weld-groove area in mm² t is the plate thickness in mm
weld. This should be treated as a preliminary planning adjustment rather than a universal prediction, as bead size, heat input and welding sequence can vary considerably between procedures. The objective should be to use the fewest passes consistent with the approved welding procedure, required weld quality and metallurgical limitations of the grade being welded. Over-welding increases consumable use, labour time, heat input and the forces responsible for shrinkage. Clamps reduce movement but not shrinkage forces Most shrinkage calculations assume that the plates are free to move. In a workshop, however, components are frequently restrained using clamps, jigs, strongbacks or dedicated fixtures. As a preliminary workshop guide: • An unclamped or freely moving joint may experience close to 100% of the calculated movement. • A lightly clamped joint may display about 60% to 70% of the calculated movement. • A heavily fixtured joint may display about 30% to 40% of the calculated movement. These percentages are indicative only. The actual result depends on fixture stiffness, tack-weld placement, component geometry, welding sequence and the point at which the restraint is released. Importantly, restraint does not eliminate shrinkage. It changes the way the fabrication responds to it. If a component cannot contract freely, part of the contraction is converted into residual stress. When the clamps are removed, some delayed movement may still occur. In highly restrained fabrications, significant stresses may remain locked into the component, potentially affecting subsequent machining, assembly or service performance. Fixtures should therefore form part of a broader distortion-control strategy rather than being used to compensate for excessive heat input, over-welding or an unsuitable joint design. Do not overlook longitudinal pull Transverse shrinkage occurs across the weld, while longitudinal shrinkage shortens the component in the direction of the weld. Longitudinal movement is generally smaller than transverse shrinkage, but it can still cause bowing, end pull and alignment problems on long seams. As a broad workshop guide, longitudinal movement of approximately 3 mm to 6 mm along a long weld seam may be sufficient to affect a precision fabrication. The actual amount will depend on the seam length, weld cross-section, heat input, component stiffness and position of the weld relative to the neutral axis of the assembly. A weld positioned away from the neutral axis can
The formula provides a preliminary indication of the transverse contraction that could occur once the deposited weld metal and surrounding heat-affected zones have cooled. It should be used as a planning tool and checked against the fabricator’s own production experience, welding procedure and, where tolerances are critical, a representative trial joint. Start with the shape of the joint The first step is to calculate the cross-sectional area of the weld groove. This is the space that will be filled with weld metal and is one of the principal factors influencing total shrinkage. The joint can be divided into simple rectangles and triangles, with the areas then added together. For a simplified single-V joint, a practical estimate is: A=( g × t )+[ t 2 ×tan ( Ө ⁄₂)]
Where: A is the groove cross-sectional area g is the root gap t is the plate thickness Ө is the included groove angle
Once the groove area has been calculated, it can be entered into the shrinkage formula to provide a more realistic expectation of how far the joint may pull across the weld. The calculation also highlights an important production consideration. An unnecessarily wide groove angle or excessive root gap increases the volume of filler metal required. This adds welding time and consumable cost while introducing more heat and greater shrinkage forces into the fabrication. Reducing unnecessary weld-metal volume is therefore one of the most effective ways to limit distortion, provided that the joint continues to meet its design, strength and accessibility requirements. Why the first pass matters most Shrinkage is cumulative, but its effect is not necessarily distributed evenly between passes. The root and early filling passes can have a particularly significant influence on angular movement because they begin pulling the joint while the surrounding structure and deposited weld section remain relatively free to respond. Later passes add more weld metal and increase the total transverse contraction. However, each pass is deposited onto an increasingly rigid weld section, and its effect will also depend on its position within the groove. As a working allowance within the supplied methodology, the calculated result can be increased by about 10% for each additional pass beyond a single-pass
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Issue 3 – 2026
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