By Matthew Doré
TWI performed a programme of inspection and characterisation of electroslag (ES) welds for a UK-based highways maintenance company, on a network-critical structure prior to the London 2012 Olympics.
The multidisciplinary non-destructive inspection of the welds was led by TWI engineers and comprised teams of specialists from different UK-based inspection companies.
The materials characterisation was performed by TWI engineers investigating weld quality, materials properties, residual stresses, fatigue crack growth rates (FCGR) and cyclic response.
Quality assessment of welds
TWI undertook an extensive programme of inspection of ES welds contained within 965m of steelwork, over 17 spans of plate girder flanges and lattice (truss) box girders (Fig. 1).
A range of non-destructive testing (NDT) techniques were used including eddy current, magnetic particle inspection, manual ultrasonic testing, phased array ultrasonic testing and alternating current potential drop.
Many of the weld locations were inaccessible by platforms and so inspection was also performed by roped access.
Approximately 600 ES welds were inspected with multiple techniques applied at each weld location.
Engineering critical assessment
As part of the on-site inspection, TWI engineers instrumented a number of critical locations using uniaxial electrical resistance strain gauges, to record the cyclic response of the structure over a period of three weeks.
Samples of the welds were removed to facilitate in-house tensile testing, fracture toughness testing, FCGR testing, chemical analysis using optical emission spectrometry, Vickers hardness testing and macro-sectioning (Fig. 2).
A rainflow analysis of the cyclic response data, results of materials testing and non-destructive inspection findings were used as input parameters for an engineering critical assessment using TWI’s CrackWise™ integrity management software.