A short presentation on: OFFSHORE PIPELINE SYSTEMS: Part 1

Why pipelines?

  • Safer
  • Environment friendly
  • Least energy requirement
  • Lowest maintenance costs
  • Minimal impact on land use pattern
  • Negligible loss of product in transit
  • High reliability

What can be transported?

  • Liquids: Crude Oil, Petroleum Products, Petrochemical Products, Chemicals, Water, LPG
  • Solids(in slurry form): Coal, Ores, Tailings
  • Gas: Natural Gas, Any other Gas

Sequence of Flow (Fig. 1):

Sequence of Flow
Fig. 1: Sequence of Flow

Offshore Pipeline and Riser System (Fig. 2):

Schematic of offshore pipeline and riser system
Fig. 2: Schematic of offshore pipeline and riser system

Stages of an Offshore Pipeline Project

Codes & Standards

  • DnV OS-F101: Det Norske Veritas, Rules for Submarine Pipeline Systems
  • ASME B 31.8: Gas Transmission and Distribution Piping Systems
  • ASME B 31.4: Liquid Transportation Systems for Hydrocarbons, LPG and Anhydrous
  • Ammonia and Alcohols
  • API 1104: Standard for Welding Pipelines and Related Facilities
  • API 1110: Pressure Testing of Liquid Petroleum Pipelines
  • NACE MR 0175: Material Requirements – Sulphide Stress Cracking Resistant Materials for Oil Field Equipment
  • IP 6 : Institute of Petroleum –Pipeline Safety Code

Stages of a Project

  • Conceptual Study
  • Feasibility Study
  • Basic Engineering
  • Detailed Engineering
  • Construction
  • Testing & Commissioning

Conceptual Study:

  • Establish System Requirement
  • Evaluate Constraints on System Design
  • Identify Interface With Other Systems
  • Develop Design Data Requirements
  • Assess Construction Methodology
  • Finalize the Concept

Feasibility Study:

  • Evaluate Technical Options
  • Eliminate Un-viable Options
  • Firming up of Process Facilities
  • Develop Broad System Specifications
  • Establish Project Cost
  • Plan Project Implementation Scheme
  • Finalize Process Scheme & Equipments

Basic Engineering:

  • Environmental & Process Data Review
  • Pipeline Routing & Size Optimization
  • Establish Requirements for
  • Surveys and Investigations
  • Material of Construction
  • Preliminary Analysis
  • Construction, Testing and Commissioning
  • Develop Implementation Schedule

Safety Aspects:

  • Environmental Parameter and Soil Data
  • Pipeline Stability
  • Shore Approaches
  • Trenching and Burial
  • Safety of Existing Facilities

Detailed Design & Engineering

  • Engineering Design Basis
  • Route Engineering & Surveys
  • Engineering analysis and Calculations
  • Specification and Job Standards
  • Engineering for Procurement
  • Drawings for Construction
  • Installation analysis and Procedures

Design Basis:

  • Basic Data
  • Design Codes and Standards
  • Design Philosophy
  • Operation and maintenance philosophy
  • Environmental Criteria
    • Installation
    • Operation
  • Criteria for engineering analysis

Route Selection:

  • Routing Considerations
  • Pipeline length
  • Sensitive areas
  • Obstructions
  • Installation Limitations
  • Crossings
  • Drilling Rig Movement / Access
  • Surveys
  • Geo-physical & Geo-technical Surveys
  • Platform Approach / Riser Face Survey

Pipeline Wall Thickness Selection:

  • Analysis / Calculations
  • Hoop Stress
  • Buckle Initiation
  • Buckle Propagation
  • Collapse Bucking
  • Local Buckling
  • Pipeline Stress Checks
  • Hoop Stress
  • Equivalent Stress
  • Analysis Tools
  • PC Based Software ‘Pipecalc’

Wall Thickness Calculation:

For Offshore Pipelines     t = (PD/2.SMYS.a) + corrosion allowance    where

  • P is the internal design pressure in psig.
  • S is the specified minimum yield strength
  • D is the pipe outside diameter in inches.
  • t is the nominal wall thickness in inches.
  • a is the design factor (0.72 for pipeline and 0.5 for riser)

Allowable Stress Limits (Fig. 3):

Allowable Stress limits
Fig. 3: Allowable Stress limits

Types of Line pipes:

  • Seamless up to 16″
  • LSAW 18” and above

Engineering Analysis:

  • Stability Pipeline (Lateral & Vertical)
  • Pipeline Expansion
  • Pipeline Spans
  • Riser
  • Analysis Tools
  • PC Based Software ‘Pipecalc’

Anti Corrosion Coatings

  • Coating Anti-Types
  • Coal Tar Enamel
  • Fusion Bonded Epoxy

Selection Criteria:

  • Service Conditions
  • Performance Record
  • Ease of Repair
  • Cost Effectiveness
  • Compatibility with Concrete Coating

Pipeline Crossing

  • Exposed Pipelines (Single / Multiple)
  • Buried Pipelines (Single / Multiple)

Analysis

  • Permissible Spans (Static & Dynamic)
  • Stress Analysis
  • Stability of Supports

Design Tools (Fig. 4):

Design tools for pipeline analysis
Fig. 4: Design tools for pipeline analysis

 

 

Anup Kumar Dey

I am a Mechanical Engineer turned into a Piping Engineer. Currently, I work in a reputed MNC as a Senior Piping Stress Engineer. I am very much passionate about blogging and always tried to do unique things. This website is my first venture into the world of blogging with the aim of connecting with other piping engineers around the world.

3 thoughts on “A short presentation on: OFFSHORE PIPELINE SYSTEMS: Part 1

  1. Dear Sir,

    Thank you for your great posts in here. I have found many interesting information from this website

    It will be very appreciate if you have a post to describe more detail consideration in stress analysis for offshore project.

    Regards,

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