Types of Pipeline in Oil & Gas Industry:
- Injection lines: Pipelines injecting water / steam / polymer / gas into the wells to improve the lift.
- Flow lines: Pipelines from the well head to the nearest processing facility.
- Trunk lines / Inter field lines: Pipelines between two processing facilities or from pig trap to pig trap or from block valve station to block valve station.
- Export lines / Loading lines: From the processing facility to the loading or export point.
- Transfer lines / Spur lines: Branch line exiting into trunk line or export line.
- Gathering lines: One or more segment of pipelines forming network and connected from the wells to processing facilities.
- Disposal lines: Pipe line which disposes normally produced water into disposal wells (shallow / deep).
- Subsea pipelines: Pipe lines connecting the offshore production platforms to on shore processing facilities.
Pipeline Typical Flow Scheme – Export Crude (Fig. 1):
Fig. 1: Figure showing Pipeline Typical Flow Scheme – Export Crude
Pipeline Typical Flow Scheme – Export Gas (Fig. 2):
Fig. 2: Figure showing Pipeline Typical Flow Scheme – Export Gas
Pipeline Typical flow scheme – Offshore (Fig. 3):
Fig. 3: Figure showing Pipeline Typical Flow Scheme – Offshore
Codes used in Oil & Gas Industries:
Design and Construction:
- ASME B31.4 – Pipeline transportation Systems for liquid hydrocarbons and other liquids
- ASME B31.8 – Gas Transmission and distribution piping systems
- ISO – 13623 – Petroleum and Natural gas industries Pipeline transportation systems
- DNV –F-101 – Offshore Standard for submarine pipeline systems
Sour Applications:
- NACE MR-01-75 – Sulphide stress cracking resistant materials for oilfield equipment
- ISO 15156 – Materials for use in H2S containing environments in oil and gas production
Materials:
- API 5L – Specification for line pipe
- API 5LC – Specification for CRA line pipe
- API 5LD – Specification for CRA clad or Lined pipe
- API 5LE – Specification for Polyethylene line pipe
- ISO 3183 – Petroleum & Natural gas industries – Steel Pipe
- ISO 14692 – Petroleum and Natural gas industries – Glass Reinforced plastic piping
- AWWA M – 45 Fibre glass pipe design
Pipeline Fittings:
- ISO – 15590 – 1 Pipeline Induction bends
- ISO – 15590 – 2 Pipeline Fittings
- ISO – 15590 – 3 Pipeline Flanges
- MSS – SP 75 – Specification for High test Wrought Butt welding fittings
- MSS – SP 44 – Steel Pipeline Flanges
- ASTM A 694 – Steel forgings for high pressure transmission service
Valves:
- API 6D – Pipeline valves
- API 594 – Check valves
- API 608 – Metal Ball Valves
- API 609 – Butterfly valves
- ISO 14313 – Petroleum & Natural gas industries – Pipeline valves
Other Pipeline Components:
- Pig launcher / Pig receivers
- Barred Tees
- Isolation Joints
- Pig signallers
- Corrosion monitoring fittings
- Shrink sleeves / External coatings / Cathodic protection for buried lines
Corrosion Threats in Oil & Gas:
- CO2 Corrosion (Sweet Corrosion) – General metal loss due to the presence of CO2 in the process fluid.
- H2S Corrosion (Sour Corrosion) – Localized metal cracking and corrosion due to presence of H2S in the process fluid.
- Chlorides and Bicarbonates – Cracking in the metal due to the presence of stress and chlorides in the process fluid.
- Corrosion due to Oxygen – Oxidation and metal loss due to the contact of metal with oxygen in the process fluid.
- Microbiologically induced corrosion – Bacteria that induces corrosion particularly within H2S
- Erosion (Abrasion) corrosion – Corrosion due to the fluid flow and velocity within the pipe environments.
- Corrosion (External) Threats in the facilities – External atmospheric corrosion on above ground lines and corrosion due to soil for buried lines.
- Corrosion Under Insulation – External corrosion due to water ingress under the insulating materials.
Material Selection Process:
- Identify corrosion threats
- Define the corrosion circuits
- Calculate the corrosion rate per year
- Calculate the Service Life Corrosion (SLC) based on design life
- Consider the materials options
- Carry out the Life Cycle Costing (LCC) – Capex / Opex / Install
- Review the materials selection w.r.t design / operating / constructability
- Finally select the choice materials
Corrosion Agents in Oil & Gas:
- Carbon Dioxide – CO2
- Hydrogen Sulphide – H2S
- Oxygen – O2
- Chlorides – Cl-
- Water – H2O
Material Options
Metals:
- CS with corrosion allowance
- Stainless Steel
- Duplex Stainless Steel
- Super Duplex Stainless Steel
Metals + Lining:
- CS with internally coated FBE
- CS with internal PE lining
- CRA clad / lined materials
Non Metals:
- Glass Reinforced Epoxy (GRE)
- Polyethylene (HDPE)
Advantages & Disadvantages of Material Options (Fig. 4):
Fig. 4: Advantages and Disadvantages of materials
Corrosion Control in Oil & Gas Pipeline Chemical Injections
Description: Purpose of injection
- Corrosion inhibitor: Basically meant for CS pipelines, forms a layer of film on the surface and protects the core pipe from corrosion attack. Batch injection or continuous
- Scale Inhibitor: Prevents scale formation in the pipelines by dissolving scale forming salts
- Wax inhibitor : Dissolves the wax within the crude
- Oxygen Scavenger : Reacts and removes oxygen in the fluid
- Biocide: Destroys the bacteria , algae and fungi in the process fluid.
- Coagulant / Anti foam: Normally mixed in the separators to improve mixing and reducing the foam
- Demulsifier: Prevents emulsion in the multiphase system
- Dehydration agents: Removes moisture in the gas normally Glycol injection
- Odorant: Added to the fluid to add smell and detect the leakage
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