Owner requested that MAD3 Engineering (formerly Deacon Engineers) assess the roofs of the tanks based on the current condition.
Scope Of Work
- Review inspection reports and current state of the roofs
- Assess current roof state for Fitness For Service (FFS)
- Determine plausible future deteriorated states of components
- Repeat FFS assessment for these deteriorated states
- Identify limit to deterioration after which roof no longer FFS
- Estimate time frame until limits reached.
Project Challenges
- Roof plate failure likely to be localized: Repair by patching with 5 mm plate
- Accurate corrosion rates should be determined through measurement over time
- Detachment of rafters greatest concern:
- Difficult to predict as connection fails (corrosion not visible without detailed inspection)
- Methods to prevent further detachment or reattach existing rafters should be investigated.
How We Managed This
- Determined from API 579/ASME FFS-1
- Relevant load case combinations and factors
- For each, deterioration conditions checked:
- Reduction in roof plate thickness
- Roof support column effective thickness
- Rafters detached from tank wall.
Value Engineering
Timeliness of the analysis as further rafter failures will mean tank roof is no longer fit for service.
