Valoración Semicuantitativa
PROPUESTAS DE MEJORA
Factors that impact on the life cycle risks are summarised qualitatively in Ta-ble 4.24. Moreover, it is indicated whether these impact on the Probability of Failure (PoF) or Consequences of Failure (CoF).
Table 4.24: Performance indicators that are relevant for life cycle health and safety risks
Performance indicator Impact on
Ease of joining Quality PoF
Mass density → weight Stability PoF Material strength Integrity PoF Strength of joints Integrity PoF Corrosion behaviour Integrity PoF Failure behaviour Integrity CoF Fire resistance Integrity PoF, CoF
The qualitative summary of the risk implications of replacing conventional steel with thinner HSLA structures is provided in Table 4.25 and the risk implications for using lightweight composite materials are summarised in Table 4.26. These capture the aspects identified in Section 4.2 that relate to health and safety risks, such as aspects related to manufacturing or operation, for example how the material properties influence the structural integrity and thus the long-term performance and durability. The confidence into the performance is assessed alongside. As discussed in the methodology chapter, the performance score PR,ij can be understood as capturing the relative changes in the likelihood of health and safety risks, whilst the impact with regard to the CoF are captured through the significance score.
A semi-quantitative assessment was carried out, similar to the one described for environmental impacts. Again, conventional steel is given the baseline value of 100, and HSLA and composites are evaluated relative to this. The scale of the scoring system is the same as for environmental impacts (refer to Table 4.20 for performance scores and Table 4.21 for significance scores).
Accordingly, the risk performance scores for conventional steel (PE,iS ), HSLA (PR,iH ) and composites (PR,iC ) are provided in Table 4.27, together with an evaluation
Table 4.25: Risk implications of replacing conventional steel with HSLA
LC stage Risk implications Performance Confidence
Initial Ease of joining: quality of joints Equal performance High Health impacts manufacturing Equal performance High
O&M Weight savings: stability Marginally better High Structural integrity: crack initiation Sightly better High Structural integrity: crack propagation Slightly worse Medium Structural integrity: corrosion of material Slightly worse Low Structural integrity: corrosion at joints Equal performance Medium Structural integrity: fire Equal performance Very high
EoL Health risks EoL Equal performance High
Table 4.26: Risk implications of replacing conventional steel with composites
LC stage Risk implications Performance Confidence
Initial Ease of joining: quality of joints Slightly worse Medium Health impacts manufacturing Slightly worse High
O&M Weight savings: stability Sightly better High Structural integrity: crack initiation Slightly worse Medium Structural integrity: crack propagation Slightly worse Low Structural integrity: corrosion of material Significantly better High Structural integrity: corrosion under joints Significantly worse Medium Structural integrity: fire Extremely worse Medium
EoL Health risks EoL Marginally worse Medium
of the significance score SR,i for each KPI. The dashed line indicates the split between initial, O&M and EoL risks.
Table 4.27: Performance scores PR,ij and significance score SR,i for risk related KPI
Conv HSLA Comp Sign
KPI PR,iS PR,iH PR,iC Si
R1 Ease of joining: quality of joints 100 100 115 4
R2 Health impacts manufacturing 100 100 115 2
R3 Weight savings: stability 100 95 85 2
R4 Structural integrity: crack initiation 100 85 115 3 R5 Structural integrity: crack propagation 100 115 115 5 R6 Structural integrity: corrosion of material 100 115 70 3 R7 Structural integrity: corrosion under joints 100 100 130 3
R8 Structural integrity: fire 100 100 150 3
R9 Health risks EoL 100 100 105 3
The relative risk performance per life cycle stage is calculated by multiplying the performance scores with the normalised significance score Si0. The total risk score Rj for each life cycle stage for conventional steel, HSLA and composites is provided in Table 4.28 and depicted in Figure 4.14.
Table 4.28: Total risk score Rji per life cycle stage
Conv steel HSLA Composites RiS RHi RCi
RjI Initial score 21.4 21.4 24.6
RjO&M O&M score 67.9 70.2 76.4
RjEoL EoL score 10.7 10.7 11.3
It can be observed that there are no additional risks of using HSLA in the initial and EoL stage. The risks in the operation and maintenance phase are however slightly increased. This is mainly due to the potential issues with pitting corrosion and faster crack propagation, because of higher stresses if thinner plates are used.
The risk of using composite materials however is significantly higher in all stages and the confidence in the material performance is significantly lower, as there is much less long-term-experience compared to using steel. Much more testing upfront and quality control after implementation is required to reduce the risks
Initial O&M EoL 0
25 50 75
Riskscore
Conventional steel HSLA
Composites
Figure 4.14: Risk score per life cycle stage
associated with composites. In particular the issues associated with the risk of a fire accident need to be addressed, but a lot of work has already been done in this area in recent years. Another key aspect is the corrosion under joints and patches, where better NDT techniques are required, which can reliably detect such issues.
Initial O&M EoL 50%
75%
100%
125%
Normalisedriskscore
Conventional steel HSLA
Composites
Figure 4.15: Risk score per life cycle stage, normalised to baseline conventional steel
4.4 Sensitivity & Uncertainty Analysis
The sensitivity and uncertainty analyses were carried out according to the method-ology proposed in Section 3.4, in order to establish which factors have the highest contribution towards the results and to identify the uncertainties associated with these factors. In other words, and referring to Figure 3.7, to identify the factors that represent potential key issues in the analysis.