The weld seam is the central connecting element in metal construction—unobtrusive in detail, load-bearing as a whole. In areas such as concrete demolition and special deconstruction, gutting works and cutting, rock excavation and tunnel construction, as well as natural stone extraction, weld seams appear in two realms at once: as structural connections on machines and tools (for example on concrete pulverizers or hydraulic rock and concrete splitters) and as joints in the structures to be processed—buildings, tanks, and steel constructions. Their quality determines safety, durability, and the behavior of components under varying, often impact-type loads—typical for deconstruction-oriented operations.
Definition: What is a weld seam
A weld seam is the material-bonded joint of two or more metallic components produced by localized heating to melting (or near the melting temperature), with or without filler metal. After solidification, the weld cross-section forms a welded joint whose properties result from base material, filler material, heat input, weld geometry, and the manufacturing process. Typical processes are arc welding (e.g., SMAW, GMAW/MAG, GTAW/TIG), submerged arc welding, resistance spot welding, as well as laser and hybrid processes. The resulting connection transmits forces in tension, compression, bending, and shear—often under dynamic and impact loading in demolition and cutting applications.
Structure, geometry, and characteristic values of the weld seam
The structure of a weld seam governs its load-bearing behavior and fatigue strength. Design and manufacturing parameters are specified in drawings and inspection requirements.
Key features
- Weld type: Butt weld, fillet weld, corner weld, T-weld, lap weld; single- or double-sided; multi-pass.
- Weld thickness and height: e.g., a-dimension (effective throat thickness) and s-dimension (weld thickness for butt welds) determine the load-bearing cross-section.
- Penetration and degree of fusion: Full or partial penetration influence stiffness and notch effect.
- Weld reinforcement and toe transition: Smooth transitions reduce notch stresses; underfill or excessive convexity are unfavorable.
- Heat-affected zone (HAZ): Region adjacent to the weld with altered microstructure; hardness, toughness, and residual stresses are decisive here.
Joint preparation and groove forms
Bevels (V-, X-, K-groove), root gaps, tack welds, and fixtures secure component position and penetration. In deconstruction-oriented applications, in which tools such as concrete pulverizers and steel shears generate high peak loads, reproducible joint preparation is a decisive factor for the service life of weld seams on load frames, bearing mounts, and adapter plates.
Weld seam in the context of demolition, deconstruction, and extraction
Weld seams are found in load-bearing steel and tank structures, in embedded parts within concrete, in piping and steel profiles, as well as on tools and hydraulic power units. In concrete demolition and special deconstruction, impact and cyclic loading cases occur; in rock excavation and tunnel construction, vibrations and abrupt load changes also act. In natural stone extraction, weld seams are primarily relevant on machine frames, cylinder mounts, and protective covers.
Practical examples
- Concrete pulverizers: Weld quality at arms, shaft and pin bearings, knife carriers, and boom connections influences load distribution when breaking concrete and cutting reinforcing steel.
- Stone and concrete splitting machines: Welded joints on reaction frames, pressure blocks, and cylinder mounts must safely introduce compressive and transverse forces when splitting wedges transmit forces into the component.
- Steel shears, combination shears, multi cutters: When cutting profiles, plates, and stiffeners, weld seams locally change stiffness; reinforcement, root passes, or doublers influence the cutting path.
- Tank cutters: Longitudinal and circumferential seams on tanks, boilers, and pipelines are mechanically stressed weld zones; changes in material thickness and doublers require adapted cutting approaches.
- Hydraulic power units and cylinders: Housings, flanges, and brackets are often welded; sealing faces and threaded bushings require low-stress transitions.
Types of weld seams and positions
The choice of weld type follows the load path and boundary conditions:
- Butt welds: Coaxial plate/profile ends; favorable load transfer, with full penetration providing high fatigue strength.
- Fillet welds: Angular connections (T-, corner, lap joints); economical but more notch-sensitive—geometry and blending are critical.
- Multi-pass execution: For greater thicknesses and better penetration control; advantageous in heavy steelwork.
- Welding positions: PA, PB, PC, PD, PE, PF—the position influences penetration, bead shape, and defect risk.
Materials, heat-affected zone, and notch effect
Structural steels, fine-grain structural steels, and wear-resistant steels respond differently to heat input. The HAZ may become locally harder and more brittle. Undercuts, notches, and abrupt transitions increase stress concentrations. In applications with concrete pulverizers or steel shears, such locations promote crack initiation under cyclic loads. Controlled heat management (preheating, interpass temperature, heat input) reduces hydrogen cracking susceptibility and residual stresses.
Quality features and assessment of the weld seam
Weld seam quality is assessed using geometric and imperfection criteria. Surface indications such as pore openings, lack of fusion, undercut, slag inclusions, or uneven weld reinforcement must be evaluated. Quality levels distinguish permissible deviations depending on function and loading; load-bearing connections on highly stressed machine structures generally require stricter criteria.
Test methods
- Visual testing (VT): Initial assessment of shape, transitions, and surface indications.
- Dye penetrant or magnetic particle testing (PT/MT): Detection of surface-breaking cracks and lack of fusion on ferromagnetic or non-ferromagnetic materials.
- Ultrasonic or radiographic testing (UT/RT): Detection of internal defects, penetration, and fusion—relevant for thicker sections and safety-critical seams.
Loading, cracks, and typical damage patterns
In deconstruction-relevant operations, variable cutting, pressing, and pulsating loads act on weld seams. Typical damage mechanisms include:
- Fatigue cracks at weld toes and in the HAZ due to fluctuating loads, e.g., during repeated crushing, cutting, or spreading.
- Hydrogen-induced cracking in high-strength steels with high hardness/stress levels.
- Lack of fusion and insufficient penetration as starting points for crack formation under impact loads.
- Pores and slag that reduce the effective cross-section and create notches.
Weld seam and cutting/splitting processes
During cutting and splitting work, weld seams influence process behavior:
- Concrete pulverizers: Weld reinforcement on steel profiles or embedded parts in concrete can locally harden the gripper seating and steer the fracture path.
- Steel shears and multi cutters: Lap joints, doublers, and root passes increase the local cross-section and section modulus; cutting forces therefore rise temporarily.
- Stone and concrete splitting machines: When spreading concrete structures with cast-in steel parts, weld seams on embedded components can deflect the crack path or lead to sudden releases.
- Tank cutters: Longitudinal and circumferential seams in vessels often feature thickness transitions and stiffeners; these weld zones require adapted cutting sequences to account for stress redistribution.
Design for manufacture and repair
The design of welded assemblies for use in demolition and extraction environments should avoid notches, guide load paths clearly, and minimize weld reinforcement. For repair and maintenance work on welded components of concrete pulverizers, stone and concrete splitting machines, shears, or power units, the following generally applies:
- Appropriate process selection and suitable filler material according to base material and loading.
- Preheating/temperature control to reduce hardness in the HAZ and the risk of hydrogen cracking, especially for thicker or higher-strength steels.
- Rework of weld toes (smooth blending) to reduce notch effects.
- Acceptance tests in line with the importance of the connection and internal specifications.
Influence of weld seams on operational safety
Weld seams on load-bearing structures of tools and machines significantly influence operational safety. Regular visual inspections, adapted test intervals, and monitoring of known hotspots (e.g., lug plates, boom mounts, force redirections) are part of an appropriate maintenance concept. In environments with impact loads and abrasive exposure, a documented condition assessment is advisable before minor indications (hairline cracks, undercuts) grow into critical damage.
Welding processes and their suitability in heavy steel construction
For thicker sections and high loads, processes with controlled penetration and stable heat input are preferred. GMAW/MAG welding is productive and common for constructions in demolition environments; SMAW (stick) is robust and suitable for field repairs; GTAW/TIG provides high seam quality with lower penetration, preferred for thinner sections, fits, or root passes. The process choice influences porosity tendency, spatter, weld surface, and rework.
Drawings: symbols, dimensions, and notes
Weld seam symbols on drawings define weld type, dimensions, location, quality level, and any post-treatment. Common specifications include the a-dimension, weld length, intermittent or continuous execution, single- or double-sided penetration, the arrow side (arrow side/other side), as well as notes on heat treatment and surface finish. For parts subjected to the forces of concrete pulverizers or steel shears, unambiguous drawing specifications are a prerequisite for reproducible manufacturing quality.
Weld seam in reinforced concrete and composite systems
In concrete components, weld seams occur mainly on embedded steel plates, connection angles, headed stud members, brackets, and inserts. During deconstruction, these connections influence demolition behavior. A combination of mechanical breaking (e.g., concrete pulverizer) and targeted cutting of steel components (e.g., steel shears) accounts for differing strengths and weld zones. During splitting operations on concrete components, cast-in welded inserts can divert crack paths or locally block them.
Safety and health protection (general)
Work around weld seams—whether processing, cutting, or repair—requires coordinated protective measures. These include, in particular, protection against falling components under load, control of potential media in vessels (gases, liquids), adequate ventilation for hot work, attention to ignition sources, and personal protective equipment. Procedures and permits must be defined and implemented project-specifically.
Documentation and traceability
For welded constructions on tools and assemblies in demolition and extraction environments, clear manufacturing instructions, qualified personnel, and traceable inspection and maintenance records are of high importance. Drawings, weld maps, test certificates, and maintenance protocols ensure quality throughout the life cycle—from manufacturing through operation to maintenance.