What Is Piping – Page 134 – A Blog to learn Piping, Mechanical, and Process Engineering Basics in a Simple Way

Offshore pipelines are the center stage of the subsea transportation system. Any offshore oil and gas projects constitute a long length of offshore pipelines. These are also known as sub-sea pipelines. In the transportation and delivery of carbon products, offshore pipelines play a major role. But the design and laying of offshore pipelines are not easy. It requires many considerations. In this article, we will explore the basics of offshore pipeline projects in brief. Why offshore pipelines? Pipelines are used for transportation and delivery services from historic times due to their own advantages like 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 through Offshore Pipelines? Offshore pipelines can be used to transport liquids, solids, and gases as per requirement. Normally the following products are used inside offshore pipelines: Liquids: Crude Oil, Petroleum Products, Petrochemical Products, Chemicals, Water, LPG Solids(in slurry form): Coal, Ores, Tailings Gas: Natural Gas, Any other Gas Flow Sequence of Offshore Pipelines Fig. 1 below shows the sequence of flow for offshore pipeline operations. Fig. 1: Sequence of Flow Offshore Pipeline and Riser System The schematic of an offshore pipeline and riser system is shown in Fig. 2 below: Fig. 2: Schematic of the offshore pipeline and riser system Stages of an Offshore Pipeline Project Codes & Standards used in Offshore pipeline projects: Various codes and standards establish the design guidelines for offshore pipeline systems. The major ones are listed below for reference: DNV OS-F101: Det Norske Veritas, Rules for Submarine Pipeline Systems ASME B31.8: Gas Transmission and Distribution Piping Systems ASME B31.4: 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 MR0175: Material Requirements – Sulphide Stress Cracking Resistant Materials for Oil Field Equipment IP 6: Institute of Petroleum –Pipeline Safety Code Offshore pipeline Project Stages All offshore pipeline projects have the following stages before it is ready to take the first fluid. Conceptual Study Feasibility Study Basic Engineering Detailed Engineering Construction Testing & Commissioning Conceptual Study In this stage for offshore pipelines, the following major activities are performed. 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 The feasibility study is a very important stage for offshore pipeline projects as it evaluates all possible options for the project to decide the feasibility. The major activities of this stage are 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 & Equipment Basic Engineering Basic Engineering is the next important stage for offshore pipeline projects. The major activities involved in this stage are listed below: 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 for offshore pipeline projects Environmental Parameter and Soil Data Pipeline Stability Shore Approaches Trenching and Burial Safety of Existing Facilities Detailed Design & Engineering The main or the most important stage of any offshore pipeline project phase is detailed engineering. Most of the design works are studied in detail and completed in this stage. 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 The engineering design basis provides all the governing criteria to follow in the pipeline project. It provides the Basic Data Design Codes and Standards Design Philosophy Operation and maintenance philosophy Environmental Criteria Installation Operation Criteria for engineering analysis Route Selection Pipe route selection for offshore pipelines is very important and it is an exhaustive activity. It includes the following considerations: Routing Considerations Pipeline length Sensitive areas Obstructions Installation Limitations Crossings Drilling Rig Movement / Access Surveys Geo-physical & Geotechnical Surveys Platform Approach / Riser Face Survey Offshore Pipeline Wall Thickness Selection The wall thickness of offshore pipelines is calculated and selected considering all possible failure stages. It includes Analysis / Calculations Hoop Stress Buckle Initiation Buckle Propagation Collapse Bucking Local Buckling Pipeline Stress Checks 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's 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 for Offshore Pipeline Systems Fig. 3 below provides the allowable stress limits for offshore pipeline and riser systems. Fig. 3: Allowable Stress limits Types of Line pipes in Offshore systems A variety of pipeline sizes is used in offshore pipeline projects. Normally following line pipes are used: Seamless up to 16" LSAW 18” and above Engineering Analysis Various engineering analyses need to be done in the complete design life cycle of offshore pipelines including the following 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 Design for Offshore Pipeline Crossing Exposed Pipelines (Single / Multiple) Buried Pipelines (Single / Multiple) Stress Analysis of Offshore pipelines Stress analysis (Both static and dynamic) must be performed for all offshore pipeline systems to ensure code and engineering compliance with Permissible Spans Stability of Supports Deflections Stresses, etc Design Tools for Offshore Pipelines Fig. 4 below lists a few of the design tools that are used for the design of offshore pipeline and riser systems. Fig. 4: Design tools for pipeline analysis Online Video Courses related to Pipeline Engineering If you wish to explore more about pipeline engineering, you can opt for the following video courses Pipeline Stress Analysis using Caesar II Design of Underground Pipeline Supports Hot Tapping in Piping and Pipeline Industry Buried or Underground Pipeline Stress Analysis using Caesar II Few more Pipeline related useful Resources for You.. Underground Piping Stress Analysis Procedure using Caesar IIComparison between Piping and Pipeline EngineeringA Presentation on Pipelines – Material Selection in Oil & Gas IndustryCorrosion Protection for Offshore PipelinesStart up and Commissioning of the Pipeline: An ArticleDESIGN OF CATHODIC PROTECTION FOR DUPLEX STAINLESS STEEL (DSS) PIPELINEAN ARTICLE ON MICRO TUNNELING FOR PIPELINE INSTALLATIONA short presentation on: OFFSHORE PIPELINE SYSTEMS: Part 1Factors Affecting Line Sizing of Piping or Pipeline Systems