Page 236 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Upset score 10/213
Medium 10 pts Offshore pipelines, in which combined streams of hydrocar-
Excursions have happened in the past in essentially the same bon gas, liquids, and water are simultaneously transported
system, but not recently; or theoretically, a real possibility often rely on onshore equipment to perform separation.
exists that a relatively simple (high-probability) event can Potential for contamination from on-line equipment mal-
precipitate an excursion. Preventive mechanisms minimize functions is as follows:
customer impacts.
Low 15 pts High 0 pts
Rare excursions have happened under extreme conditions. Excursions are happening or have happened recently. Customer
Highly effective and reliable prevention mechanisms exist to impacts occur or are only narrowly avoided (near misses) by
correct these rare occurrences. Customer impacts are almost preventive actions.
nonexistent. Medium 10 pts
None 20 pts Excursions have happened in the past in essentially the same
System configuration virtually disallows contamination possi- system, but not recently; or theoretically, a real possibility
bility. A customer impact never occurred in the present sys- exists that a relatively simple (high-probability) event can
tem configuration. High reliability, redundant measures are precipitate an excursion. Preventive mechanisms minimize
employed to virtually eliminate the possibility of customer customer impacts.
impact. Low 15 pts
Rare excursions have happened under extreme conditions.
Because products often originate at facilities not under the Highly effective and reliable prevention mechanisms exist to
control of the pipeline operator, he can reduce the risk in only correct these rare occurrences. Customer impacts are almost
certain of limited ways. Preventive actions for point-of-origin nonexistent.
contamination episodes include None 20 pts
System configuration virtually disallows contamination
Close working relationship with third-party suppliers possibility. A customer impact has never occurred in the pres-
(inspections, quality monitoring, control charts) ent system configuration. High reliability, redundant measures
Monitoring of all pipeline entry points (and possibly even are employed to virtually eliminate possibility of customer
upstream of the pipeline-in the supplier facility itself-for impact. No processingequipment is in use.
early warning) to detect contamination or potential contami-
nation at earliest opportunity The following prevention activities can be factored into the
0 Redundant decontamination equipment for increased relia- evaluation for excursions due to equipment malfunctions:
bility
0 Arrangements of alternate supplies to shut off offending 0 Strong equipment maintenance practices to prevent mal-
sources without disrupting pipeline supply functions
0 Plans and practiced procedures to switch to alternate sup- Redundancy of systems (backups) to increase reliability of
plies to ensure quick, reliable moves to backup suppliers equipment or systems to reduce the probability of overall
0 Automatic switching to alternate supplies for the quickest failures
possible reaction to excursions 0 Early detection of malfunctions to allow action to be taken
0 Operator training in human error prevention techniques to sup- before damaging excursions occur.
port prompt and proper detection and reaction to excursions.
A3. Pipeline dynamics
Any preventive actions should be factored into the assess-
ment ofcontamination potential. Another contamination source is liquids or solids introduced
into a product stream by a change in pipeline system dynamics.
A2. Product equipment maljunctions A possible source of solids could be rust particles displaced
from the pipe wall. To cause this, rust would have to be present
Pipeline equipment designed to remove impurities on-line can initially. An accompanying event could be a significant distur-
malfunction and allow contaminants to enter the product bance to the pipe that displaces a large amount of rust at one
stream. Some on-line equipment such as dehydrators serves a time. Liquids are another possible contamination source. It is
dual role of protecting the pipeline from possible corrosion not uncommon for free liquids, both water and heavier hydro-
agents and eliminating product contamination. Hence, their carbons, to be present in low-lying areas of a pipeline. This
reliability in preventing contamination will overlap previous often occurs in spite of precautionary measures to dry the gas
analysis of their reliability in preventing internal corrosion. prior to injection into the pipeline. Water and hydrocarbon
Equipment that is designed to introduce foreign substances liquids are often atomized and suspended In the gas stream.
into the product stream can also be a source of contamination. Changes in gas stream pressure, velocity, or temperature
Normally, the foreign substances must be kept within a certain can cause droplets to form and condense in the pipe. As a liquid,
concentration range in order to perform their intended function the water and hydrocarbons will gravity flow to the low points
without adversely affecting the product. Corrosion inhibitor of the pipeline. If gas stream velocity is later increased, the
liquids or flow-enhancing chemicals are two examples of liquids may move as a slug or liquid droplets will be picked up
injected substances. Equipment malfunction or flow regime into the gas and carried along the line. It is conservative to
changes may introduce a higher concentration of these prod- always assume the presence of free liquids. Pigging or analysis
ucts than what was intended. during high-flow conditions often verifies this assumption.