Weld fatigue improvement terminology in brief
No. The different terms belong at different levels.
‘Weld fatigue improvement’, the improvement of the fatigue strength of the weld, is the overall aim. ‘Geometric improvement’ is one of two methods for achieving that aim, and residual stress improvement is the other.
Geometric improvement is achieved using ‘weld profiling’, whereby stress concentration factors (SCFs) are removed. SCFs include weld seam flank angle, weld toe radius and weld toe defects.
Residual stress improvement using ultrasonic peening (UIT) or other mechanical impact methods alters the residual stress state in the weld toe from tensile to compressive, thereby delaying crack initiation.
Weld grinding and weld shaving describe two distinct mechanics for doing weld profiling: grinding removes material abrasively, producing dust. Machining cuts material away, producing collectible and reusable metal shavings.
Why weld profiling terminology matters in specifications and procurement
These five terms are often used loosely and interchangeably in day-to-day industry writing and conversation, but they are not synonyms.
Each describes a different level of the same subject: an overall goal, a family of methods, a specific technique, a tool or process, and, in the case of ‘weld shaving’, a byproduct-defined variant of the process of improving the fatigue strength of a weld.
Understanding the distinction matters when specifying, procuring, or auditing weld profiling work, since a specification that calls for the ‘grinding’ of a weld seam does not mean the uniform ‘profiling’ of a weld seam to a specific cross-sectional shape including a pre-defined weld toe radius transition from weld seam to base plate.
Weld fatigue improvement: post-weld fatigue strength improvement defined
‘Weld fatigue improvement’ is referred to in DNV-RP-C203 as post-weld fatigue strength improvement and is the umbrella term for any technique deliberately applied to a weld after welding to improve its fatigue strength and fatigue life beyond the as-welded condition.
It is defined by outcome, not by method, so the term covers any technique that measurably improves fatigue strength/fatigue life, regardless of how that improvement is achieved.
Geometric improvement vs. residual stress improvement (HFMI and ultrasonic peening)
DNV-RP-C203 and the International Institute of Welding (IIW) recognise two distinct methods leading to weld fatigue improvement outcomes:
- Geometric improvement, whereby the cross-sectional shape of the weld seam is altered, in part or entirely, and stress concentration factors (SCFs) are removed. Primary SCFs are weld seam flank angle, weld toe radius and weld toe defects. These factors ‘attract’ and concentrate the stresses created in welded steel structures during fatigue loading. Such stress concentrations will over time become weak points and can lead to crack initiation, especially in high-cycle fatigue regimes.
- Residual stress improvement, whereby the residual stress state at the weld toe is converted from damaging tensile residual stress into beneficial compressive stress, through methods such as ultrasonic peening or other high-frequency mechanical impact (HFMI) treatments.
Weld profiling: geometric improvement of the entire weld seam
Within the geometric improvement family, weld profiling refers to a specific target outcome: reshaping the entire weld seam (both the weld cap and the weld toe) into a continuous, large-radius transition to the base plate.
As covered elsewhere in this FAQ series, this distinguishes it from weld toe grinding, a narrower geometric improvement technique that treats only the toe and leaves the weld cap flank angle unaddressed. Weld profiling is defined by what part of the weld it treats (the whole seam) and by the geometry it produces, not by the tool used to produce it.
Weld grinding: an abrasive method, not a target geometry
Weld grinding describes a tool and process, not a result: abrasive material removal using belt, disc, or burr grinders. Because grinding has, for decades, been effectively the only practical way to carry out weld profiling, the terms weld grinding and weld profiling are frequently used interchangeably in industry — and DNV-RP-C203 itself refers to “machining or grinding” when describing this practice. But the terms describe different things: weld profiling specifies the geometry to be achieved; weld grinding specifies one abrasive method of achieving it. As an abrasive process, grinding removes material as fine dust and airborne particulate — a distinction that becomes significant when comparing it with weld shaving.
Weld shaving (weld machining): dust-free, cutting-based weld profiling
Weld shaving (or weld machining) is the term for a cutting-based approach to geometric improvement — using a machining tool rather than an abrasive one to remove the weld cap and undercut material. The distinction in the name reflects the distinction in the physical process: a cutting tool removes material as continuous shavings or cuttings — solid metal swarf, the same kind of byproduct produced by any conventional metal-cutting operation — rather than as the fine dust generated by grinding.
Current fatigue design standards do not draw this distinction explicitly; DNV-RP-C203 groups material-removal methods loosely under “machining or grinding.” But the distinction is physically real and practically significant, because the byproduct of the process has direct consequences for the fabrication working environment.
Grinding dust from steel is a recognised occupational health hazard, linked to respiratory issues on prolonged exposure, and it is difficult to contain in the large open fabrication halls used to build monopile and tower sections. Metal shavings produced by a cutting process are, by contrast, a solid, contained, and recyclable byproduct — generated without dust and, in the case of Maxars’ CNC-robotic TM401 system, at meaningfully lower noise levels (approximately 80 dB, comparable to a domestic vacuum cleaner) than abrasive grinding.
Weld fatigue improvement, profiling, grinding and shaving: how the terms fit together
The five terms sit in a hierarchy rather than meaning the same thing: weld fatigue improvement is the goal; geometric improvement is one of the two families of method used to reach it (the other being residual stress alteration); weld profiling is the specific geometric improvement technique that reshapes the entire weld; weld grinding names the traditional abrasive tool historically used to perform weld profiling; and weld shaving names the cutting-based alternative — the method Maxars applies with the TM401 — which achieves the same profiled geometry as grinding, but removes material as collectible shavings rather than as dust.
Sources: DNV-RP-C203, Fatigue design of offshore steel structures (October 2024 edition), DNV. P. J. Haagensen & S. J. Maddox, IIW Recommendations on Post Weld Improvement of Steel and Aluminium Structures, revised 16 February 2004. Maxars TM401 Operational Performance and Technical Data Sheet.