The risk assessment framework described here is very robust. It can be used for any pipeline material, service (product transported), component, etc. It can also be used for non-pipeline systems and components including subsurface storage caverns. Yes, even geologic formations used for subsurface storage of fluids can be efficiently risk-assessed by methodologies outlined here. For some applications, there will be nuances in segmentation and handling of certain phenomena. However, changes in the risk assessment platform are not needed.
Following are discussions and lessons learned when applying the risk assessment framework to various pipeline types, materials, component types, system types, products, geographic locations (including offshore). The focus here is on pipelines and pipeline-like systems–anything involving transport (and transport-related activities) of fluidized products (gas, liquids, slurries, etc) through continuous conduits.
System
The word ‘system’ has many uses here. It is used in context such as safety system, control system, management system, procedure system, training system, to indicate a collection of parts or sub-systems. While no set definition exists, a pipeline system normally refers to a large collection of pipeline segments and related stations/facilities.
Pipeline Types
Pipeline systems are often categorized into types such as transmission, distribution, gathering, offshore, and others, as discussed in . All types are appropriately assessed using the same methodology.
Pipe, pipeline, component, facility
As used here, a pipeline segment can be any length of pipe, not necessarily a ‘joint’ length. A component is a part of a pipeline that is other than a pipe segment and can be a flange, valve, fitting, tank, pump, compressor, separator, filter, regulator, or any of many other portions of a typical pipeline. A pipeline is a collection of pipe segments and components. A facility is similarly a collection of segments and components but usually with more variety than simply pipe. A system is one or more pipelines and associated facilities. See also the discussion of segmentation for purposes of assessing risk.
Risk concepts covered here are meant to apply to any segment of pipe, component, entire pipeline, facility, or system. While pipe is often used to illustrate a concept, the concept also applies to any other component.
As a convenience, the terms component and segment will be used most often in these discussions.
The basic risk concepts also apply to all component material types. While steel is often the focus of discussion, risks associated with all other materials of construction such as plastic, cast iron, concrete, and others, can be efficiently assessed using these same methods.
Owner/Operator references are used interchangeably here, both referring to the decision-makers who control choices in pipeline design, operations, and maintenance.
As previously noted, there are admittedly, some nuances when assessing risk of certain components. For instance, consider threaded and other mechanical connections.
Mechanical Connections
When a threaded, flanged, or other mechanical connection leaks, the leak is often classified as ‘material failure’ or some similar but incorrect classification. We say incorrect because material failure is not a failure mechanism but rather the result of some failure mechanism. ‘Material failure’ explains nothing until the failure mechanism is identified.
Any mechanical connection such as a threaded connection, is efficiently modeled as susceptible to degradation similar to corrosion or cracking. In the case of threaded connections, the threads and gasket or sealant, if present, form the containment envelope. That envelope relies on friction as part of its sealing ability and is susceptible to ‘degradation’ from, for example, vibrations which reduce the needed friction.
Just as corrosion is modeled as metal loss–the containment envelope is degrading–the threaded connection can be modeled in an analogous way. Just as with corrosion or cracking, mpy measures the loss of sealing ability and ‘effective’ wall thickness (across interlocked threads) as the surrogate for that sealing ability. Loss of this theoretical wall thickness as stand-in for sealing ability occurs from sources similar to cracking: fatigue cycling from thermal or mechanical origins, vibrations from rotating equipment, wind, wave action, etc.
Facilities
Facility, station, etc refers to one or more occurrences of, and often a collection of, equipment, piping, instrumentation, and/or appurtenances at a single location, typically where at least some portion is situated above-ground (unburied). Facilities and their subparts are efficiently assessed using the same methodology.
So, by ‘facilities’ we usually mean tank farms, pump stations, marine loading/unloading, metering sites, etc, typically within fences and with multiple equipment types, having above- and below-grade components, sometimes surface storage (tanks, vessels), and distinct from most ROW miles which hold only line pipe. A facility can be as small as a single valve site or as complex as a hydrocarbon processing plant. Facility components can include:
- Above and below-ground piping
- Pumps/Compressors
- Tanks/Vessels
- Valves
- Fittings
- Filters, Strainers
- Flanges and other mechanical connectors
- Meters, gauges, transmitters, and other instrumentation
- Branches, tees, elbows, small threaded or welded connections, and other appurtenances
- Offshore platforms
A challenge in facility risk assessment will be in inventorying the various components that might be present. Especially for large, complex, or older facilities, complete databases of all components may not be available.
Ideally, so-called ‘smart CAD’ (computer assisted drawing) files will be available to not only have a complete and tabulated inventory of components but also to show the interconnectivity of those components (so that flow pathways are known). When such databases exist, the risk assessment can advance most efficiently.
Segmentation, a key element in producing the risk assessment, will emerge from the database of components or, when not present, from whatever list can be created.
If a PPM (Predictive Preventative Maintenance) program is in place, that may also provide good segmentations of key equipment. Since a PPM program is designed to account for differences in failure potential for all components, it parallels a risk assessment in an important way.
Distribution Systems
The risk assessment framework here must often accommodate a wider variety of materials, including joining processes, over longer era’s of installation, and in more urban environments. Records availability is also often more problematic in distributions systems compared to transmission systems.
Collectively, these issues are all related to data. Any risk assessment suffers when data availability is low.
- Segmentation
- Materials
- Leak rates
- Odorization
Offshore
While the same risk assessment framework is completely suitable for this application, it is worthwhile to take note of differences in the offshore environment. Beyond the more obvious accessibility issues are unique surroundings sometimes discovered, including constantly shifting seabottom conditions, ship wrecks, war munitions dump sites, and others.
- Environmental differences
- Installation stresses
The dynamic nature of pipeline operations offshore often makes the risk picture more complex than onshore operations. A further complication is the common practice of idling offshore pipelines. For economic and technical reasons, it is not unusual for a pipeline to be abandoned for long periods of time until economic conditions change to warrant its return to service or until technology overcomes some obstacle that may have idled the line. Many lines are ultimately placed in a service for which they were not originally designed. Pressures, flow rates, velocities, and the composition of the products transported change as new fields are added or existing fields cease production. Ownership of the pipelines can change as new operators feel that they can increase the profitability of an operation.
Another aspect of offshore pipeline operations is the higher costs associated with most installation, operation, and maintenance activities. When pipelines are placed in an environment where man cannot live and work without special life-support systems, additional challenges are obvious. Inspection, maintenance, repair, and modification requires boats, special equipment, and personnel with specialized skills. Such operations are usually more weather limited and proceed at a slower pace than similar onshore operations, again adding to the costs.
Offshore systems are often more vulnerable to weather-related outages, even when no damage to equipment occurs. This is covered in the cost of service interruption assessment.
As with onshore lines, historical safety data of offshore pipeline performance are limited. We cannot currently make meaningful quantitative correlations among all of the factors believed to play a significant role in accident frequency and consequence. The factors can, however, be identified and considered in a more qualitative sense, pending the acquisition of more statistically significant data. For these reasons, and for the sake of consistency, an indexing approach for offshore lines that parallels the onshore pipeline analysis is often the most useful risk assessment option.
Offshore pipeline systems are either transmission pipelines—long, larger-diameter pipelines going to shore—or pipelines associated directly with production—flow lines, gathering lines. For purposes of this risk assessment, the two categories are treated the same. The scoring for the offshore risk model will parallel very closely the onshore model for transmission lines described in Chapters 3–7. Although this chapter is primarily aimed at ocean and sea environments, most conce pts will apply to some degree to pipeline crossings of rivers, lakes, and marshes.
Risers, commonly defined as the portion of the pipeline from the sea bottom up to a surface platform (sometimes including pig traps and valves on the platform), can be evaluated as part of the pipeline system or alternatively, as part of a risk assessment for facilities like platforms. Note that abandoned facilities may also be included in an assessment as a potential threat to public safety if consequences from the facility are identified (navigation hazard for surface facilities, threat of flotation, etc.). In that case, the risk assessment will need to include the probability and consequences of those particular hazards even when no leak/rupture scenario is plausible.
Offshore CoF
As with onshore spills, the type of product spilled, the distance to sensitive areas, and the ability to reduce spill damages will govern the consequence potential for offshore lines. Spills offshore can be assessed as they are in the onshore risk assessment model. This involves assessment of product hazard, spill size, dispersion potential, and vulnerable receptors.
More minor impacts seen in the offshore environment during normal operations include the possible impact on marine life from pipeline noise/vibrations during operations and the presence of the pipeline as a barrier to marine life movements. These can be addressed in an evaluation of receptor vulnerabilities.
Gathering Systems
Same risk assessment
- leak rates
- materials,
- pressures,
- product quality
- inspectability
- standard of care in design, installation, maintenance
Water Systems
- Materials
- Leak rates
- Pressures
- Equipment/asset types
- Consequences
Underground Storage
- Depleted hydrocarbon caverns
- Salt dome caverns
- CO2 sequestration
- Segmentation–polar coordinate system
- Failure modes
- Communication vs leak
- Components
- Geologic formation
- casing, tubing, packer, valve, wellhead
- Inspections
- See CFER report to PHMSA
Also includes cavern boundaries, so geotechnical and 3-D considerations impacting dynamic segmentation and ‘failure’ definitions
Components
- Fittings
- Current
- Discontinued Practice
- Mitre joint
- Acetylene weld
- Mechanical couplers
- Wrinkle bend
- Repair Devices
- Current
- Sleeves
- Clamps
- Discontinued Practice
- Saddles
- “Orange Peel”
- patches
- plugs
- pumpkins
- Current
- Historically problematic (ie, increased leak potential)
- stopple fittings
- Dresser couplings
- appurtenances using elastomeric materials for seals
- plus, ‘discontinued practice’ items above
See also ‘materials’
Materials
- Steel
- Cast iron
- Ductile iron
- Plastics
- Concrete
- Clay
- Wood
- gaskets, seals, sealants, coatings
CO2 Pipeline Systems
Special considerations are warranted for designing, operating, and maintaining CO2 pipelines and sequestration facilities.