Real Data, Real Problems, Real Solutions (and some generic examples)
Getting Started Examples
A simple overall example
- Conceptual-Only (ballpark estimates using deductive reasoning only)
- Rudimentary RA (example 1 from book, using groupings prior to dynamic segmentation)
- Better RA (example 2 from book, some basic calcs for two threats)
- Examples discussed in video training
- Examples in published articles
- Modern PoF as part of QRA
Risk Management
- Patrol vs slab (PMM)
- “The $200 Anomaly”
- ILI vs DA
- ILI vs check valves
- less atm corr inspection
- offshore burial after storm
- above-ground vs buried plastic vs steel
- reaction to population changes
- storage facility buffer
Examples from Textbook
- PoF
- CoF
- Svc interruption
ALARP
Consider a catastrophic pipeline accident involving the death of two individuals and the loss of the pipeline with an estimated event frequency of 10-5 per mile-year. The threshold for disproportionate cost, using a disproportionality factor, is illustrated as follows:
The values and units in this example are:
10-5 accidents of this type per mile per year
58 miles length of pipeline
$10M cost of fatality
2 person fatality per accident
6 is disproportionality factor, based on some guidance documents suggesting factors between 2 and 10
$1.5M additional cost per accident for other losses
(10-5 × 58) accidents/year × ($10,000,000 × 2 + $1,500,000)/accident × 6 = $75,000/year
In this example, $21.5M is the cost of an accident of this type; $12,500 is the annual risk from an accident of this type; and the $75,000/year value is a theoretical maximum amount to be spent to reduce the chance of that accident. This is heavily influenced by the disproportionality factor.
When potential spending becomes ‘grossly disproportionate’ to the risk reduction benefits, it is not warranted. It serves no stakeholder to spend resources inefficiently.
This threshold for disproportionate cost is used in the following way:
All risk reduction measures that could be implemented are listed, in order of their cost/benefit ratio. All of these measures, up to the point of the cost/benefit exceeding 6, should be implemented before the risk would be determined to be ALARP and additional spending to reduce it is not warranted.
At the extreme, a maximum value of $75K is a reasonable expenditure if all of the $12.5/year risk is eliminated (not realistic).
Certifications
See a sample scenarios with 3 pipelines carrying different products through similar routing. Sketch with sample database.
Data Workarounds
- Test of time evidence
- ERA of manufacture/construction considerations
- Degradation of ‘evidence’
Related to Regulations
thoughts and considerations for regulatory waiver requests (eg, class location changes, alternative inspection technology, % smys allowance, etc)
Pressure Testing
The risk assessment can begin with an estimate of wall thickness required to hold the test pressure based on simple formula such as the Barlow formula for hoop stress. Then, to account for surviving defects and possibly other loadings (longitudinal stresses, etc), a conservatism adjustment can be applied to the calculated wall thickness.
For instance, if the hoop stress calculation suggests a wall thickness of 0.200 inches is required to hold the pressure of the test then perhaps only 80 or 90% of this value is used as the wall thickness implied by the pressure test, eg 0.160″ to 0.180″, depending upon the level of conservatism desired.
Let’s say the pressure test was done 10 years ago and other parts of the risk assessment estimate a degradation rate of 10 mils per year. Then the best estimate of pipe wall thickness today, based on the 10 year old pressure test would be the implied wall thickness (say 0.160″) less 10 * 10 = 100 mils so 60 mils of wall thickness remaining today (0.060″).
Estimating Pipe Wall Thickness
Assemble all the evidence:
- pressure test records
- ILI results
- NDE records
- NOP (recent values)
- Era of manufacture
- Era of construction
- Pipe effective wall
- Pipe available wall
- Handling defects/weaknesses
The most compelling evidence will be information with the highest accuracy and timeliness. So, each piece of evidence must be adjusted for age and accuracy before comparing to other evidence. Sometimes the evidence will be conflicting.
Design/Construction
- Building a database during construction
- HDD