Material Selection in Oil & Gas Industry

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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

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

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

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

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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