200% Peening Coverage: Why OEMs Require It and How to Measure It
200% coverage is becoming the OEM standard. The rationale, the measurement methods (visual, PeenScan, colorimetry) and the Airbus and Boeing specs.
Definition of 100% coverage
100% coverage is reached when the part surface shows contiguous impact dimples, with no un-impacted area visible under a 10x binocular magnifier. This is the minimum AMS 2430 requirement.
Why 200%?
200% coverage corresponds to twice the exposure time required to reach 100%. This requirement is imposed by certain customers (notably Airbus on primary structure) to guarantee statistical homogeneity of the residual stresses, even in the presence of micro-defects or process variation.
Measurement methods
Visual (10x magnifier)
The historical method: subjective and operator-dependent. 200% is difficult to assess visually (it cannot be told apart from 150%).
Fluorescent tracer (PeenScan / Tracer Technology)
A fluorescent layer is applied before peening and read under UV. Erosion of the layer correlates with the cumulative number of impacts. Excellent resolution between 80% and 200%+.
Colorimetry
Coloured marking applied before peening, optical density measured afterwards. An economical alternative to fluorescent tracers.
Major OEM specifications
- Airbus ABP 1-4010: 200% on primary structure
- Boeing BAC 5730: 100% standard, 200% on rotating components
- Safran 10 4001: 150% to 200% depending on the fatigue criterion
Operational recommendations
On primary-structure aerospace parts, we systematically recommend: coverage verification by PeenScan on the first batch and a cross-check every 20 parts, an exposure time of 2.2× the theoretical 100% time (safety margin), and mandatory photographic documentation.
Coverage and intensity: two distinct requirements
Coverage (the percentage of surface impacted) and Almen intensity (the energy of the treatment) are two independent parameters within the same specification: a part can reach 200% coverage at an out-of-tolerance intensity, and vice versa. Each is verified separately — coverage by PeenScan or binocular magnifier, intensity by a saturation curve on Almen strips. Our online Almen saturation curve calculator details how the curve is built and the most frequent reading errors.
Training operators to read coverage
Coverage control remains an operator’s visual judgement: it is the point most often raised during process audits. The shot peening training course (4 days, AMS 2430 / SAE J442 / J443 framework) deals specifically with coverage reading, saturation curve construction and masking. If a part specification looks ambiguous to you, tell us what you need — we reply within 12 business hours.