Pipeline Engineering is a specialized branch of engineering with its own terms and definitions. Here is a comprehensive list of these terms and definitions.

1. Assembly : An arrangement of pipes and components such as a crossing, a pig trap, a block valve station or a riser.
2. Barred tee : Tee-piece provided with bars across the internal bore of the branch pipe to prevent entry of a pig.
3. Block valve : Valve for interrupting the flow or to shut-in a section of a pipeline. A block valve is normally either fully opened or fully closed.
4. Branch pipe : Pipe connected to a pipeline of equal or larger diameter, using a tee-piece.
5. Cold bend : A bend made from linepipe at ambient temperature, normally on the construction site, using a mechanical bending machine.
6. Commissioning : An activity where the fluid to be transported is initially introduced into a pipeline.
7. Consequence : The result of an event in terms of human safety, damage to the environment and economic loss.
8. Design factor : Ratio of the hoop stress created by the design pressure and the SMYS of the pipeline material.
9. Design pressure : The internal pipeline pressure used in the determination of the pipeline wall thickness requirements.
10. Emergency shutdown valve : Valve for isolating a pipeline from a plant in case of emergency situations within the plant.
11. Flammable fluid : A flammable fluid has a flash point lower than 100 °C.
12. Flowline : A pipeline transporting untreated hydrocarbons and other reservoir fluids.
13. Fluid : A substance which is transported through a pipeline in liquid or gaseous phase, or a combination of these.
14. Hot bend : A bend made under factory conditions by hot working billets, plates or pipes.
15. Incidental pressure : Pressure occurring in a pipeline with limited frequency and during limited periods of time. Incidental pressures include surge pressures, and thermal pressures if not occurring a significant portion of the time.
16. Injection line : A pipeline transporting gas, water or other fluids for injection into a well or a group of wells.
17. Isolation valve : Valve for isolating a pipeline from a plant connected to it.
18. Line pack : In a gas transmission system, the line pack is the quantity of gas in excess of the gas inventory in the system required to meet deliveries. The line pack is used to continue deliveries for some period following interruption of supply upstream.
19. Liquid hold-up : Quantity of liquids present in a two-phase pipeline.
20. Loading line : A pipeline between an onshore facility and an offshore loading facility, e.g. a single point mooring.
21. Maximum allowable incidental : The maximum pressure that is allowed by pressure ANSI/ASME B31.4/8 to occur in a pipeline with a limited frequency and during limited periods of time.
22. Maximum allowable operating : The maximum pressure at which a pipeline is pressure allowed to be operated under steady state process conditions, in accordance with ANSI/ASME B31.4/8.
23. Maximum operating temperature : The maximum temperature to which the pipeline or section of pipeline is expected to be exposed during normal operational activities, including start-up and shut-down operations, but excluding abnormal situations, e.g. fires.
24. Minimum operating temperature : The minimum temperature to which the pipeline or section of pipeline is expected to be exposed during normal operational activities, including start-up and shut-down operations, controlled blowdown, but excluding abnormal situations, e.g. pipeline ruptures.
25. Off-plot : A location outside designated plant boundaries.
26. Offtake line : A pipeline transporting fluid from a larger pipeline.
27. On-plot : A location inside designated plant boundaries.
28. Operating envelope : A defined set of key parameters or parameter ranges which must be adhered to during operation of the pipeline in order to prevent loss of technical integrity.
29. Overpressure protection valve : Valve intended to protect the pipeline against overpressure by preventing pressure from a source building up in the pipeline.
30. Pig : A device which can be propelled through a pipeline by fluid flow and normally used for cleaning, batching, inspection or other activities.
31. Pig trap : An ancillary item of pipeline equipment, with associated pipework and valves, for introducing a pig into a pipeline or removing a pig from a pipeline.
32. Pipeline : A system of pipes and other components used for the transportation of fluids, between (but excluding) plants. A pipeline extends from pig trap to pig trap (including the pig traps), or, if no pig trap is fitted, to the first isolation valve within the plant boundaries or a more inward valve is so nominated.
33. Pipeline code : An industry or national code written for the purpose of designing, constructing and operating pipelines.
34. Pipeline end manifold (PLEM) : An item of subsea equipment, comprising piping and valves, at the end of a pipeline, to which single point mooring hoses are connected.
35. Pipeline leak : An uncontrolled fluid release from a pipeline.
36. Plant : An installation, such as well-head, processing facility, pressure boosting station, storage tank, offshore platform, refinery, etc., with defined boundaries and which is not normally accessible to the public.
37. Pre-commissioning : A series of activities, including cleaning and possibly drying, executed to prepare the pipeline for commissioning.
38. Pressure equalisation line : Small bore pipe with valves to allow equalisation of pressure across a larger valve, avoiding damage to the seats of the larger valve.
39. Pressure relief safety valve : Valve for protecting a pipeline against overpressure by releasing fluid from the pipeline.
40. Remote vent line : A pipeline used for discharging light gaseous fluids to atmosphere.
41. Riser : A vertical, or near vertical, section in a pipeline.
42. Risk : The product of the probability of an event occurring and the consequences of the event when it has occurred.
43. Sectionalising block valve : Main valve for sectionalising a pipeline, in order to limit the release of line contents in case of pipeline leak or rupture.
44. Shore approach : That section of a pipeline which crosses the sea shore, or major river/estuary shores. The shore approach includes the area of breaking waves and extends to the highest water mark.
45. Single point mooring (SPM) : A device for mooring a ship and transferring fluid between a pipeline and that ship.
46. Slugcatcher : A device located at the downstream end of a two-phase pipeline, for the primary separation of the liquid and gas phases, and the temporary storage of liquids generated by pigging and transient flow conditions. There are two types of slug catchers: the vessel type and the finger type.
47. Specified minimum yield stress : The level of stress which produces 0.5 percent total (SMYS) strain (API definition). This stress is specified by the Principal and guaranteed by the Manufacturer/Supplier.
48. Sphere : A spherical shape pig, used for batching and liquid hold-up removal in two-phase pipelines.
49. Sphere tee : A jacketed tee-piece with a perforated inner pipe to prevent entry of a sphere into the branch pipe.
50. Spurline : A pipeline transporting fluid into a larger pipeline.
51. Stable fluid : A stable fluid has an NFPA reactivity grade number of zero.
52. Surface safety valve : Valve, part of the well-head assembly, applied as isolation valve between flowline and wellhead.
53. Surge pressure : Pressure due to mass flow velocity changes, caused by operational activities, e.g. valve closures, pump shut-down or start-up.
54. Technical integrity : Technical integrity of a facility is achieved when, under specified operating conditions, there is no foreseeable risk of failure endangering safety of personnel, environment or asset value.
55. Test pressure : The pressure at which the pipeline will be or has been tested for strength.
56. Thermal pressure : Pressure due to thermal effects on the fluid in the blocked-in pipeline or blocked-in pipeline sections.
57. Toxic fluid : With reference to EP-55000 Section 40 Part 1, toxic fluids include all fluids in the slightly toxic, toxic and highly toxic categories.
58. Trunkline : A main transmission pipeline to which spurlines and offtake lines may be connected.
59. Two-phase pipeline : Pipeline transporting fluids where both the liquid phase and the gas phase are present at pipeline pressure and temperature conditions.