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Offshore Pipeline Systems

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Offshore Pipeline Systems

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Contents

1 Pipeline Design 1 1.1 Overview of pipeline components 1 1.2 General Design procedures 3 1.3 Design for strength 6 1.4 Design for internal fluid pressure 7 1.5 Design for Upheaval Buckling 10 1.6 Design for Hydrodynamic Stability 11 1.7 Design for Operating Stress and Strain 16 1.8 Pipeline Spanning and Control 21 1.9 Design of Pipeline Risers 26 1.10 Pipeline Survey, Mapping and Routing 38 1.11 Pipeline Shore approaches 41

2 Pipeline Materials 47 2.1 Metallurgy and manufacture of offshore pipes 47 2.2 Effects of Treatment of pipeline steel 53 2.3 Flexible and Composite pipelines 53 2.4 Design of high pressure and high temperature pipeline 61

3 Fluid flow through pipes 65 3.1 Flow assurance characteristic 65 3.2 Basic hydrodynamics 68 3.3 Multi-phase flow 70 3.4 Hydrate formation / prevention 73 3.5 Wax formation / prevention 77 4 Pipeline Construction 83 4.1 Construction by Lay Barges 83 4.2 Construction by Reel Barges 91 4.3 Construction by Pull and Tow method 92 4.4 Construction of Pipeline Trenching method 94 4.5 Construction of Pipe-in-Pipe method 96 4.6 Construction of Pipeline Bundles 98 4.7 Construction of Flexible pipelines 102 4.8 Construction of Cross country pipeline 105 5 Pipeline Installation 111

5.1 Pipe Lay Installation Methods 111 5.2 Design code for pipeline installation 112 5.3 S-Lay Installation 112 5.4 J-Lay Installation 113

5.5 Reel Lay Installation 114 5.6 Tow-in Installation 116 5.7 Flex-Lay Installation 120 5.8 Multi-Lay Installation 121 5.9 Allowable Installation Stresses / Fatigue 121 6 Pipeline Corrosion / Protection 127 6.1 Internal Corrosion by fluid flow 127 6.2 External Corrosion on pipelines 129 6.3 Microbial Induced Corrosion (MIC) 134 6.4 Corrosion Protection by Coating 137 6.5 Cathodic Protection (CP) 141 6.6 Coating Protection against Mechanical Damage 147 6.7 Concrete Weight Coating for Stability 150 6.8 Pipeline Thermal Insulation 154 7 Pipeline Commissioning, Operation and Maintenance 161 7.1 Pipeline pressure testing and pre-commissioning 161 7.2 Pigs and Pigging operations 164 7.3 Pipeline Integrity Management 172 7.4 Pipeline Inspection, Monitoring and Testing 177 7.5 Leak Detection and Emergency Planning 179 7.6 Defect Assessment 183 7.7 Intervention, Repair and Mitigation 185 7.8 Risks, Reliability and Safety 186 7.9 Environmental and Regulatory requirements 187 Appendix A: Welding Pressure Pipeline & Piping Systems 189 Appendix B: Practical Exercises 239

2

Pipeline Materials

This chapter covers the metallurgy and manufacture of pipeline in offshore oil and gas industry,

including Rigid, Flexible and Composite pipes and their chemical compositions, grades available in the

market. Both low temperature, and high pressure and high temperature pipelines are illustrated.

Learning Objectives Various metallurgy and manufacturing methods for steel pipes Effective treatment of pipes requirement Important points on using seamless, ERW, SAW and Spiral pipes Flexible and Composite pipeline construction and their application HPHT pipelines-Simple design calculations

2.1 Metallurgy and Manufacture of Offshore Pipes

Design of pipeline for oil and gas applications is based on the following parameters: 1. Manufacturing process of pipelines-Seamless, SAW or DSAW, ERW, Spiral weld 2. Metallurgy of piping material-Chemical composition and mechanical strength 3. Size of the pipe-Diameter and wall thickness 4. Piping grade application for Shallow and Deep water 5. Codes and Standards followed

Manufacturing Process The manufacture of individual pipes of any standard lengths, which are manufactured in a pipe mill, refers to the individual pieces as it shipped out of the mill and does not represent the how the pipes are formed in a continuous pipeline in the field.

In some cases, pipe is shipped to the pipeline construction site as "double joints," where two pieces of pipe are pre-welded together to save time. Most of the pipe used for oil and gas pipelines is seamless or longitudinally welded, although spirally welded pipe is common for larger diameters.

Seamless Pipe The seamless tubes, are the pipes without any welded joints like SAW, DSAW or ERW, but as one solid tube shape manufactured by the following processes:

(a) Extrusion process:

This process is used for small diameter tubes only. The bar stock is cut to length and heated to 2,280 °F (1,250 °C) before being sized and descaled. The billet is then extruded through a steel die. After

48 Offshore Pipeline Systems

extrusion, the final tube dimensions and surface quality are obtained with a multi-stand reducing mill. Common applications: Hydraulic system high pressure lines. (b) Mandrel Mill

This process is used to make smaller sizes of seamless pipe, typically 1 to 6 inches (25 to 150 mm) diameter. The ingot of steel is heated to 2,370 °F (1,300 °C) and pierced. A mandrel is inserted into the tube and the assembly is passed through a rolling (mandrel) mill. Unlike the plug mill, the mandrel mill reduces wall thickness continuously with a series of pairs of curved rollers set at 90° angles to each other. After reheating, the pipe is passed through a multi -stand stretch-reducing mill to reduce the diameter to the finished diameter. The pipe is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing. (c) Plug Mill

This process is used to make larger sizes of seamless pipe, typically 6 to 16 inches (150 to 400 mm) diameter. An ingot of steel weighing up to two tons is heated to 2,370 °F (1,300 °C) and pierced. The hole in the hollow shell is enlarged on a rotary elongator, resulting in a short thick-walled tube known as a bloom. An internal plug approximately the same diameter as the finished diameter of the pipe is then forced through the bloom. The bloom containing the plug is then passed between the rolls of the plug mill. Rotation of the rolls reduces the wall thickness. The tube is rotated through 90° for each pass through the plug mill to ensure roundness. The tube is then passed through a reeling mill and reducing mill to even out the wall thickness and produce the finished dimensions. The tube is then cut to length before heat treatment, final straightening, inspection, and hydrostatic testing.

Longitudinally Welded Saw Pipe Submerged Arc Welded pipes (SAW) is a tubular product made out of flat plates, , which are formed, bent and prepared for welding. The most popular process for large diameter pipe uses a longitudinal seam weld. Double submerged arc welded (DSAW) pipe is welded pipe whose longitudinal butt joint is welded in at least two passes, one of which is on the inside of the pipe; the welds are made by heating with an electric arc between the bare metal electrode. Pressure is not used. Filler metal for the welds is obtained from the electrodes. For diameters above 36 inches, double seam welded pipe is specified as an alternative in API 5L. This has two longitudinal seams 180° apart, formed by the SAW process. Finished pipes are normally 40 feet (12 m) or sometimes 60 feet (18 m) long, depending on the capacity of the pipe mill and the ease of transport to the pipeline.

ERW Pipe & HFI Welded Pipe Originally this type of pipe, made using Electrical Resistance Welding (ERW), which contains a solid phase butt weld, using resistance heating to make the longitudinal weld (ERW), but now-a-days, most pipe mills now use High frequency induction heating (HFI) for better control and consistency.

Lack of fusion due to insufficient heat and pressure is the principal defect in this type of pipes. As a result of these problems, ERW pipe was generally regarded as a second-grade pipe suitable only for low pressure applications. In addition, the standard of heat treatment of the weld line, which is necessary to ensure good toughness, was found to be important and some specifications call for local weld line heat treatment using induction coils followed by full body normalizing of the whole pipe in a furnace. As a result of these improvements, modern ERW/HFI pipe has much better performance than the traditional product and has been accepted by a number of operators for high pressure gas transmission.

Spiral Welded Pipe As an alternative process, spiral weld construction allows large diameter pipe to be produced from narrower plates. The defects that occur in spiral welded pipe are mainly those associated with the SAW weld, and are similar in nature to those for longitudinally welded SAW pipe. An additional problem with early spiral welded pipe was poor dimensional accuracy, particularly out of roundness at the pipe ends. This led to problems of poor fit-up during field girth welding. it is considered suitable only for

Pipeline Materials 49

low pressure applications such as water pipe. However, modern spiral line pipe from a premium quality supplier is of a quality equivalent to straight seam welded pipe, and it has been used extensively in Canada and Europe for high pressure gas pipelines in grades up to API X70.

Metallurgy of Piping Material

Chemical Composition And Mechanical Strength Carbon Steel Seamless Pipe-API 5l Standard: API 5L,ASTM A106 Application: Fluid pipe, petroleum pipe, structure Pipe, API steel pipe, precision steel pipe, precision tube Process: Cold drawn steel tube, cold rolled tube, hot rolled steel tube, ERW steel pipe, LASW pipe, SSAW pipe. Steel Grade: A, B, X42, X46, X52, X56, X60, X65, X70 Outer Diameter: Seamless (1/4"~24") ERW (8"~24") LSAW (16"~64") SSAW (8"~100") Wall Thickness: Sch20, Sch30, Sch40, Sch80, Sch160, Sch XXS, Sch STD

Table B.1 Size tolerance

OD Tolerance WT Tolerance A, B X42 ~ X70

D<60.3mm +0.41/-0.40mm D<73mm +20%/-12.5% D<73mm +15%/-12.5% D>=60.3mm +0.75/-0.40mm D>=73mm +15%/-12.5% D>=73mm +15%/-12.5%

Table B.2

Chemical Composition %

PSL1 PSL2 Grade C (Max.) Mn(Max.) P(Max.) S(Max.) C (Max.) Mn(Max.) P(Max.) S(Max.) A 0.22 0.90 0.03 0.03 0.22 1.20 0.025 0.015 B 0.26 1.20 0.03 0.03 0.22 1.30 0.025 0.015 X42 0.26 1.30 0.03 0.03 0.22 1.40 0.025 0.015 X46 0.26 1.40 0.03 0.03 0.22 1.40 0.025 0.015 X52 0.26 1.40 0.03 0.03 0.22 1.40 0.025 0.015 X56 0.26 1.40 0.03 0.03 0.22 1.40 0.025 0.015 X60 0.26 1.40 0.03 0.03 0.22 1.45 0.025 0.015 X65 0.26 1.45 0.03 0.03 0.22 1.65 0.025 0.015 X70 0.26 1.65 0.03 0.03 0.22 1.85 0.025 0.015


Table B.3

Mechanical properties - PSL 1

Grade Yield Strength(Min.) Tensile Strength(Min.) Elongation Ksi MPa Ksi MPa

E=1944 A 0.2 /U 0.9

B 35 241 60 414 X42 42 290 60 414 X46 46 317 63 434 X52 52 359 66 455 X56 56 386 60 414 X60 60 414 63 434 X65 65 448 66 455

Table B.4

Mechanical properties - PSL 2

Grade Yield Strength Tensile Strength Elongation Min Max Min Max

E=1944 A 0.2 / U 0.9

Ksi MPa Ksi MPa Ksi MPa Ksi MPa B 35 241 65 448 60 414 110 758 X42 42 290 72 496 60 414 110 758 X46 46 317 76 524 63 434 110 758 X52 52 359 77 531 66 455 110 758 X56 56 386 79 544 71 490 110 758 X60 60 414 82 565 75 517 110 758 X65 65 448 87 600 77 531 110 758

Seamless and Welded Austenitic Stainless Steel Pipe

Standard: ASTM A312/ASME SA312 Material: 304, 304L, 304H, 310S, 316, 316L, 316H, 316Ti, 321, 321H, 347, 347H Size: OD(6-1016mm) x WT(1-50mm) Application: Used in Pipeline for transporting corrosive fluid. Inspection items:

1. Chemical Composition 2. Size 3. Mechanical Properties 4. Flattening Test 5. Hydrostatic Test or Eddy current test or Ultrasonic test 6. Surface quality, straightness

Negotiated items:

1. Erosion test 2. Intercrystalline corrosion 3. Stabilization heat treatment.


Table B.5

OD Tolerance

NPS ASTM A312 OD Tolerance + -

inch mm inch mm 1/8~1 1 /2 >1 1 /2~4 >4~8 >8~18 >18~26 >26~34 >34~48

1/64(0.015) 1/32(0.031) 1/16(0.062) 3/32(0.093) 1/8(0.125) 5/32(0.156) 3/16(0.187)

0.4 0.8 1.6 2.4 3.2 4.0 4.8

1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031) 1/32(0.031)

0.8 0.8 0.8 0.8 0.8 0.8 0.8

Table B.6

Wall Thickness Tolerance

NPS ASTM A312 WT Tolerance ,% + -

1/8-2 1 /2 20.0 12.5 3~18,t/D≤5% 22.5 12.5 3~18,t/D>5% 15.0 12.5 ≥20, welded 17.5 12.5 ≥20, seamless,t/D≤5% 22.5 12.5 ≥20,seamless,t/D>5% 15.0 12.5

Table B.7

Chemical Composition %

Material ASTM A312 Chemical Composition % Max C Mn P S Si Cr Ni Mo N B Nb Ti

TP304 0.08 2.00 0.045 0.030 1.00 18.0-20.0 8.0-11.0 … … …. …

TP304H 0.04-0.10 2.00 0.045 0.030 1.00 18.0-20.0 8.0-

11.0 … … … …

TP304L 0.035 D 2.00 0.045 0.030 1.00 18.0-20.0 8.0-

13.0 … … … …

TP310S 0.08 2.00 0.045 0.030 1.00 24.0-26.0 19.0-22.0 0.75

TP316 0.08 2.00 0.045 0.030 1.00 16.0-18.0 11.0-14.0

2.00-3.00 … … …

TP316L 0.035 2.00 0.045 0.030 1.00 16.0-18.0 10.0-14.0

2.00-3.00 … … …

TP316H 0.04-0.10 2.00 0.045 0.030 1.00 16.0-18.0 11.0-

14.0 2.00-3.00 … … …

TP316Ti 0.08 2.00 0.045 0.030 0.75 16.0-18.0 10.0-14.0

2.00-3.00 0.10 … 5x(C+

N)-0.70

TP321 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-12.0 … 0.10 … 5C -

0.70

TP321H 0.04-0.10 2.00 0.045 0.030 1.00 17.0-19.0 9.0-

12.0 … … … 4C -0.60

TP347 0.08 2.00 0.045 0.030 1.00 17.0-19.0 9.0-13.0 10xC-

1.00 …

TP347H 0.04-0.10 2.00 0.045 0.030 1.00 17.0-19.0 9.0-

13.0 … … 8xC-1.00 …

Table B.8

API-5L-Carbon Steel-Welded Line pipe-Chemical Composition

Table B.9

API-5L-Carbon Steel-Seamless Line pipe


2.2 Effects of Treatment of Pipeline Steel

Post Weld Treatment Welding pipe sections together sounds easy enough. But when the pipe is destined for the tough conditions of North Sea oil and gas fields, post-weld heat treatment is essential. The Induction treatment has been helping pipelines survive in one of the world’s harshest environments.

Figure B.1

High Frequency Induction Heater

A High Frequency (HF) induction heater locally melts the mating surfaces, and the pressure causes them to weld together. The heat input is kept at the optimum level by closed-loop computer control of heaters. The induction treatment, assist the heat treating of the approximately 2600 welds involved in the pipelines. Post-weld treatment is needed to relieve stress in the metal caused by the welding, and also to prevent hydrogen cracking in the metal, a common cause of metal failure in subsea environments. The induction system used with a closed-loop chiller and a temperature control unit and split induction coils for the pipelines.

Post-welding heat treatment is generally not necessary for areas of carbon steel which are less than 3" (8cm) thick. For those which are, after welding, reheat the weld area to 150° C. When necessary, cover the weld area with an insulating material such as a thermal cloth. This will retard the cooling rate and reduce the welding stresses induced into the component. In either case, after the procedure is complete, 100% magnetic particle inspection should be performed on the welds. Any cracks discovered must be repaired according to the procedure before the part is used. In the SAW line pipes, heat treatment should be applied to control the mechanical properties, such as, strength and toughness. At present Quenching-Tempering and Normalizing-tempering are employed for seamless and SAW pipes In recent years, steel products have been demanded to meet quality requirement of ever increasing severity. Because the sulphur content in pipeline steel has great effect on the properties of the steel, it should be reduced to less than 0.0020%, better less than 0.0010%. Therefore, special processing technology is required from hot metal pretreatment and steelmaking modules to refining processes. The degasser has the function of heating by oxygen blowing (RH-OB) for the production of ultra low carbon steel, so it is utilized for decarbonization, deoxidation, dehydrogen, as well as composition and temperature control.

2.3 Flexible and Composite Pipelines

Flexible Pipelines The Flexible pipes have been used in oil and gas applications including production, gas lift, gas injection, water injection and various ancillary lines such as potable water and liquid chemical lines. The main application field such as, static flow lines, dynamic and static risers, subsea jumpers, topside jumpers and expansion joints.


In deep water applications, the flexible pipes are mainly used for dynamic risers from a subsea pipeline end manifold (PLEM) or from a riser tower to a floating production system such as FSO, FPSO and TLP. Flexible pipe is an unbounded structure consisting of helically wound metallic armour wires or tapes combined with concentric layers of polymers, textiles, fabric strips and lubricants. Flexible pipe size range from 2.5” to 16” inner diameter and can withstand pressures up to 15,000 psi for small bores and 4000 psi for the larger bores. For high temperature services, it can withstand as high as 130C for both static and dynamic services. A typical construction of a flexible pipe from the manufacturer “ NKT Flexibles” is shown below.

Figure B.2

Typical Construction of Flexible pipe

(1) Carcass

An interlocking structure manufactured from a stainless steel strip. The carcass prevents collapse of the inner liner and provides mechanical protection against pigging tools and abrasive particles. Stainless steel AISI 316L type or Duplex 2101 are the standard choices for carcass. They are resistant against general corrosion, pitting corrosion and chloride induced cracking. For more corrosive environments Duplex stainless steel grades such as Duplex 2205, Duplex 2507 or nickel based alloys grades may be applied. (2) Inner liner

An extruded polymer layer providing internal fluid integrity. The inner liner is manufactured from thermoplastic polymer materials such as High Density Polyethylene (HDPE), cross-linked Polyethylene (XLPE), Polyamide (PA) or Polyvinylidene Fluoride (PVDF). The choice of material is dependent upon service condition. (3) Pressure armour

A number of structural layers consisting of helically wound C-shaped steel wires and/or steel strips. The pressure armour layers provide resistance to radial loads. The pressure armour layers are typically manufactured from low carbon steel – suitable for the specified service whether sweet or sour. Several different steel grades are available dependent upon the specified service condition.

Figure B.3

Pressure Armour Profile


(4) Tensile armour

A number of structural layers consisting of helically wound rectangular steel wires. The layers are counter wound in pairs. The tensile armour layers provide resistance to axial tensile loads. The tensile armour layers are typically manufactured from low carbon steel – suitable for the specified service whether sweet or sour. Several different steel grades are available dependent upon the specified service condition. (5) Outer sheath

An extruded polymer layer. The function is to shield the pipe’s structural elements from the outer environment and to offer mechanical protection. The outer sheath is manufactured from Polyamide (PA) or Medium Density Polyethylene (MDPE) extruded on to the structure as the outermost layer.

There are additional layers may also be made, such as, Anti-wear layer and Insulation layer.

The Anti-wear layer is a non-metallic layer that are inserted between the structural elements to prevent wear and tear between the structural elements.

The Insulation layer of material of low thermal conductivity can be applied in order to obtain specific thermal insulation properties of the pipe.

The choice of material depends on high pressure, high temperature, sour service (high H2S and/or CO2 content and super deep water etc.

The End Fittings of Flexible Pipe Flange connectors are manufactured to standards specified by the clients, eg. API 6A, ASME B16.5-1996, Grayloc type, techloc type, SPO type etc.

Figure B.4

End Fitting

Figure B.5

Bend Restrictor


Ancillary Equipment Accessories critical for the flexible pipe configuration such as bend stiffeners, bend restrictors, buoyancy systems, clamps, tethers, clump weights , etc.

Figure B.6

Buoyancy System

Advantages of Flexible Pipe

Purpose designed product optimized for each specific application A design that combines the flexibility of a polymer pipe with the strength and

weight of a steel pipe Follows the natural contours of seabed thus eliminating the susceptibility to free

pipeline spans Minimization of external corrosion effects owing to encapsulation of the steel

armour inside a continuous polymer outer sheath Accommodate misalignments during installation and tie-in operations Diverless installation is possible - no metrology required Load-out and installation safer, faster and cheaper than any other pipe application Retrievability and reusability for alternative application thus enhancing the overall

field development economics and preserving the environment Excellent inherent thermal insulation properties Good corrosion resistance against transported fluids, incl. water injection

applications

The Design of Flexible Pipes Use the Following Codes and Standards: API RP 17B Recommended practice for flexible pipe API RP 17J Specification for Unbonded Flexible pipe API RP 17K Specification for Bonded Flexible Pipe API RP 2RD Design of risers for floating production systems (FPSs) and Tension-Leg Platforms ISO 10420 Flexible pipe systems for subsea and marine riser applications

Composite Pipes

What is a Composite Pipe?

In the most general of definitions, a composite consists of “Two or more dissimilar materials which when combined are stronger than the individual materials.” This general definition covers the various types of pipe currently being used in the transmission of oil and gas which includes metal, plastic, and thermosetting resin pipe as well as various combinations of these three types. A more precise definition for thermosetting composites would be “a combination of a reinforcement fiber in a thermoset polymer resin matrix, where the reinforcement has an aspect ratio that enables the


transfer of loads between fibers, and the fibers are chemically bonded to the resin matrix.” The characteristics of composites that make them ideal candidates for natural gas transmission include resistance to chemical and cathodic corrosion, high strength, light weight, and flexibility. Generally speaking, composites have a higher strength-to-weight ratio that steel. With the ability to control the type, amount and direction of application of the reinforcement material, composite pipe becomes an ideal candidate for widely varying pressure applications The deep-water offshore oil industry need a strong, lightweight materials to replace the heavy alloy piping used on oil platforms in seawater. By reducing the weight of the piping materials on the service deck of a tension leg platform (TLP), the buoyancy of the TLP would increase. This would reduce the amount of structural steel needed below water, thereby significantly reducing the cost of a TLP. Although carbon steel and copper nickel alloy pipe had traditionally been used on offshore platforms, advanced composites were known to be stronger, more resistant to corrosion, and lighter than steel. For example, composite pipe with a 6-inch diameter weighs 4 pounds per foot, whereas copper nickel pipe with the same diameter weighs 24 pounds per foot. Advanced Composite also cost less initially than steel piping and have a longer life cycle. The estimated life cycle of composite piping in seawater was 20 years, compared to 7 years for steel piping.

The Applications of Composite Pipes Bondstrand GRE pipes and fittings are used for various offshore applications including Fire water, Potable Water, Cooling Water, Produced Water, Fresh Water, Produced process Water, Black/Grey water, Closed & Open Deck Drains, Column piping vents, Seawater Filtration, Pressure vessels, Tanks, Filtration vessels, and Caissons. These are typically shown in the figure below.

Figure B7

Application of Composite pipes


Cooling Water Grade : Bondstrand 2410 and 3410 are filament wound GRE pipe systems Pipe size : 2” -40” (50 – 1000mm) M.O.P : 10 bar (145 psi) up to 50 bar Safety factor : 4:1 Operating temperature : 121C Internal full vacuum : Size 2’ – 40” Fire endurance : L3 Electrical Conductivity : Conductive Fire Water Grade : Bondstrand 2420 and 3420 are filament wound GRE pipe systems Pipe size : 2” -40” (50 – 1000mm) M.O.P : 20 bar (290 psi) Safety factor : 4:1 Operating temperature : 93C - 121C Internal full vacuum : Size 2’ – 40” Fire endurance : L3 Electrical Conductivity : Conductive Standard : ISO 14692 Fire Water-Dry System Grade : Bondstrand 2000 WD and 7000 WDare filament wound GRE pipe systems Pipe size : 2” -16” M.O.P : 16 bar (232 psi) Safety factor : 4:1 Operating temperature : 93C Fire endurance : 10 minutes Dry and 3 hours Wet Protection : External UV protection Electrical Conductivity : Conductive Standard : ISO 14692 Drains Grade : Bondstrand 2000M and 7000M are filament wound GRE pipe systems Pipe size : 1” -16” M.O.P : 16 bar (232 psi) Safety factor : 4:1 Operating temperature : 121C Internal Pressure : Full vacuum Protection : External UV protection Electrical Conductivity : Conductive (7000m) Standard : ISO 14692 Caissons/Column Piping, and Potable Water Grade : Bondstrand 2000M and 7000M are filament wound GRE pipe systems Pipe size : 1” -16” (25 – 400mm) M.O.P : 16 bar (232 psi) Safety factor : 4:1 Operating temperature : 121C Internal pressure : Full vacuum Fire endurance : L3 Electrical Conductivity : Conductive (7000M) Protection : External UV protection Standard : ISO 14692


Process Pipe Work Grade : Bondstrand 2420 and 3420 are filament wound GRE pipe systems Pipe size : 2” -40” (50 – 1000mm) M.O.P : 25 bar (362 psi) Safety factor : 4:1 Operating temperature : 93C - 121C Internal full vacuum : Size 2’ – 40” Fire endurance : L3 Electrical Conductivity : Conductive Standard : ISO 14692

Sea Water Grade : Bondstrand 2410 and 3410 are filament wound GRE pipe systems Pipe size : 2” -40” (50 – 1000mm) M.O.P : 10 bar (145 psi) up to 50 bar Safety factor : 4:1 Operating temperature : 121C Electrical Conductivity : Conductive Standard : ISO 14692 Pressure Vessels Grade : Bondstrand 2416 and 3416 are filament wound GRE pipe systems Pipe size : 2” -40” (50 – 1000mm) M.O.P : 16 bar (232 psi) Safety factor : 4:1 Operating temperature : 93C –121C Protection : External UV protection Electrical Conductivity : Conductive Standard : ISO 14692 The Fibers The structural properties of composite materials are derived primarily from the fiber reinforcement. In a composite, the fiber contributes high tensile strength, enhancing properties in the final part, such as strength and stiffness while minimizing weight. Glass Fiber The vast majority of all fibers used in the composites industry are glass. Glass fibers are the oldest and, by far, the most common reinforcement used in non-aerospace applications to replace heavier metal parts. Glass weighs more than carbon, but also is more impact-resistant. Depending upon the glass type, filament diameter, sizing chemistry and fiber form, a wide range of properties and performance levels can be achieved. Fiber properties are determined by the fiber manufacturing process and the ingredients and coatings used in the process. During glass fiber production, raw materials are transformed into delicate and highly abrasive filaments, ranging in diameter from 3.5 to 24 micrometers. Silica sand is the primary raw ingredient, typically accounting for more than 50 percent of glass fiber weight. Metal oxides and other ingredients can be added to the silica, and processing methods can be varied to customize the fibers for particular applications

High-Performance Fibers High-strength fibers used in advanced composites include not only carbon, glass and aramid, but high-modulus polyethylene (PE), boron, quartz, basalt, ceramic, newer fibers such as poly p-phenylene-2,6-benzobisoxazole (PBO), and hybrid combinations, as well. The basic fiber forms for high-performance composite applications are bundles of continuous fibers called tows. A carbon fiber tow consists of thousands of continuous, untwisted filaments, with the filament count designated by a number followed by “K,” indicating multiplication by 1,000 (e.g., 12K indicates a filament count of 12,000). Tows may


be used directly, in processes such as filament winding or pultrusion, or may be converted into unidirectional tape, fabric and other reinforcement forms.

Carbon Fiber The most widely used fiber in high-performance applications — is produced from a variety of precursors, including polyacrylonitrile (PAN), rayon and pitch. The precursor fibers are heated and stretched to create the high-strength fibers. The first high-performance carbon fibers on the market were made from rayon precursor. PAN- and pitch-based fiber have replaced rayon-based fiber in most applications, but the latter’s “dogbone” cross-section often makes it the fiber of choice for carbon/carbon (C/C) composites. PAN-based carbon fibers are the most versatile and widely used. They offer an amazing range of properties, including excellent strength — to 1,000 ksi — and high stiffness. Pitch fibers, made from petroleum or coal tar pitches, have high to extremely high stiffness and low to negative axial CTE. Their CTE properties are especially useful in spacecraft applications that require thermal management, such as electronic instrument housings. Although they are stronger than glass or aramid fibers, carbon fibers are not only less impact-resistant but also can experience galvanic corrosion in contact with metal. Fabricators overcome the latter problem by using a barrier material or veil ply — often fiberglass/epoxy — during laminate layup. Aramid Fibers Composed of aromatic polyamide, provide exceptional impact resistance and tensile strength. Standard high-performance aramid fiber has a modulus of about 20 Msi and tensile strength of approximately 500 ksi. Renowned for performance in bulletproof vests and other armor and ballistic applications, aramid fiber has been in increasing demand, due, in part, to growth of the personnel protection and military armor markets spurred by conflicts around the world. Aramid’s properties also make the fiber an excellent choice for helicopter rotor blades, solid rocket motors, compressed natural gas (CNG) tanks and other parts that must withstand high stress and vibration.

Polyethylene (Pe) Fibers Commercially available ultrahigh-strength, high-modulus polyethylene (PE) fibers are well known for their extremely light weight, excellent chemical and moisture resistance, outstanding impact resistance, antiballistic properties and low dielectric constant. However, PE fibers have relatively low resistance to elongation under sustained loading, and the upper limit of their use temperature range is about 98°C/210°F. PE fiber composites are used in racing boat hulls, ski poles, offshore mooring ropes and other applications that require impact and moisture resistance and light weight but do not need extreme temperature resistance. At least one aircraft manufacturer now uses high-modulus PE fibers for the bulletproof insert in cockpit doors.

Design Issues of Composite Pipes Typical FRP pipe is reciprocally filament wound with a fiber angle of ±54.75° relative to the longitudinal (0°) axis. This satisfies stress loads in both the circumferential (hoop) and longitudinal (axial) directions for most pipes and pressure vessels. It withstands the in-use pressure, thermal expansion and contraction, and the surge loads induced by thrust due to water pressure, as well as the normal bending and tensile loads that may occur during installation. All of these factors must be considered in the design of the overall piping system, which includes the pipe, fittings and supports such as the anchors, guides and hangars (typically steel) that hold the pipe in place. It is preferable to filament wind fittings, such as elbows, Ts, laterals, reducers, crosses and Ys, with the same materials used to construct the pipe itself. This ensures a high degree of stability and safety. Pipe manufacturers typically line pipes with the same resin as that used in the structural laminate of the pipe wall. A corrosion- resistant veil (a thin, nonwoven fibrous reinforcement) is often incorporated into the liner. Fiberglass piping is usually joined by adhesive bonding or butt-welding. Adhesively bonded joints fall into two main types: straight-by-taper and taper-by-taper. Straight-by-taper means a slightly larger socket is integrally wound at one end of the pipe, and a mating “spigot” is shaved to a slightly smaller diameter to ensure a close fit. As the spigot is forced into the socket to a fixed stop point, all air is purged out of the joint and the resin adhesive ensures a good bond. For some larger diameter pipe, the taper-by-taper joint adhesively bonds mating male/female tapered ends, although some special tools can


be required for tapering. Butt-welding or butt-and-strap methods use hand layup to join two pipe ends of the same diameter. The two ends are butted together and the joint is wrapped with resin-wet layers of chopped-strand mat and woven roving, the same materials that are used in the pipe itself. Both adhesive joining and butt welding require trained personnel and proper surface preparation to achieve good results. A mechanical O-ring bell and spigot seal lock joint is a third option sometimes employed for a long length of large-diameter pipe. To join composite pipe to metallic pipe or equipment, a composite flange is either wound or bonded onto the pipe, then bolted to pumps, valves or other metal equipment on-site. Other, proprietary mechanical couplings are offered by manufacturers to mate composites with metallic fittings. But methods that require penetration of the composite pipe wall should be avoided, since breaking the fibers decreases the pipe’s performance properties. In addition to its light weight and high strength-to-weight ratio, composite piping’s corrosion resistance is another big advantage. In contrast to steel pipe, which corrodes quickly when exposed to seawater, composites are virtually corrosion-free when made with chemical-resistant resins. For platform components such as column pipe (pipe that extends from the platform down below the water surface to supply seawater) and firewater systems, corrosion resistance means years of maintenance- free service for fire pipe, composites are actually cheaper than the copper/nickel alloy that is typically used. Bonded joints eliminate the need for steel welding, which is a potential fire source on platforms with flammable hydrocarbons.

It should be remembered, however, that composite pipes can be damaged by concentrated impact loading, which can happen if they are dropped or struck by heavy objects.

Fiberglass piping is non-conductive (i.e., an insulator) and therefore does not provide a path to earth for static electricity.

To make FRP pipe conductive, conductive carbon fiber can be added to its glass fiber reinforcements or carbon powder can be added to its resin systems.

Regulations and Standards for Composite Pipes and Materials

ASTM F-1173-95 Standard Specifications for Thermosetting Resin Fiberglass Pipe and Fittings to be used for Marine Applications

ASTM D 3517 Fiberglass Pressure Pipe AWWA C950-95 Fiberglass Pressure Pipe BS 7159 Code of Practice for Design and Construction of Glass Reinforced Plastic

(GRP) Piping Systems for Individual Plants or Sites BS 6464 Specifications for Reinforced Plastic Pipes, Fittings and Joints for Process

Plants DNV-OS-C401 Fabrication of Offshore Structures ISO/DIS 14692 Petroleum and Natural Gas Industries — Glass-Reinforced Plastics

(GRP) Piping ISO/DIS 15649 Petroleum and Natural Gas Industries — Piping Systems —

General Requirements NTS NORSOK Standard M-CR-621 GRP Piping Materials

2.4 Design of High Pressure and High Temperature Pipeline

Common Terms used in HP/HT Pipeline design

Plastic Strain – Plastic strain is mechanical strain that remains when the loading is removed. Ratcheting – Ratcheting is the process of accumulating additional deformation beyond what


would occur with static loading only because of a combination of static, cyclic loading and asymmetric loads are applied to the plastic range and the total deformation increases with each cycle until a failure limit is reached. Asymmetric load – The maximum and minimum stresses in the cycle are not equal in magnitude, but are of opposite sign. Upheaval Creep – This is a form of ratcheting of the material surrounding a buried pipeline that allows the pipe to rise toward the surface due to cycles of loading. Pipeline design for high temperature and pressure may involve plastic strain in the hoop direction. The risk of ratcheting failure has been considered for some designs. Stress-strain diagrams are shown in DNV-OS-F101, Submarine Pipeline Systems (2000).requires that operating temperature and design pressure shall cause plastic deformation only on the first cycle of operation.

Operation at high temperature relative to the original laying temperature may provide a sufficient source of compressive force that a pipeline laid on the seabed can buckle like a bar in compression. Such a global buckling mode may involve upward motion as in upheaval buckling, downward motion at a free span or lateral motion. The lateral buckling modes are easier to excite than vertical modes on a flat seabed. Estimates of the axial and bending stresses induced within the buckles suggest that these can be large enough to cause concern for local buckling within the larger global buckle. Buckling resistance is a function of the material and pipe configuration, so that flow lines with low D/t ratios can be designed to avoid local buckling within such a global buckle. For buried pipe or pipe with a weight covering, for example, dumped rock or concrete mattresses, the direction of least constraint for buckling will be upward or downward in a covered free span. Cyclic forces that induce buckling may allow a buried pipeline to move upward through the covering layer. This is known as “upheaval creep”.

Design of high-temperature and pressure pipelines requires special attention, because of high thermal stresses. The following parameters have to be considered:

(a) Thermal expansion (b) Stresses in bends of expansion loops (c) Pipe’s interaction with soil characteristics (Friction and lateral resistance) (d) Pre-stressing of pipelines

The buried pipelines are operated more and more at elevated temperatures and pressures. Examples of this are flow lines carrying (untreated) gas or oil from a so-called satellite towards a treatment facility, both onshore and offshore, and district heating transmission pipelines. Flow lines are typically operated at elevated temperatures and pressures of above 100 bar, whereas District Heating systems are designed for pressures ranging from 16 bar up to 30 bar. The minimum required wall thickness of high-pressure pipelines is generally governed by the hoop stress criterion, limiting the circumferential stress caused by internal overpressure to a fraction of the yield strength. Adopting an allowable stress approach for high temperature and high-pressure pipelines, by limiting the Von Mises equivalent stress to a percentage of the yield strength

Thermal Expansion A pipeline loaded by temperature and pressure will expand near a free end such as an expansion loop. The axial movement is counteracted by soil friction, acting against the outside of the casing of the insulated pipeline. At a certain distance from the free end the friction force (summated friction over the moving pipe length) is in equilibrium with the normal force of the steel inner pipeline. This is the so-


called virtual anchor point, where thermal expansion is fully restrained. The magnitude of thermal expansion and the bend parameters determine the stress level encountered in expansion loops. The design factor for internal pressure, ranges from 1.39 to 2.22 and depends on the product being transported (e.g. hot water, oil or gas), as well as the location class. Normally a design factor F of 1.5 is used for onshore pipeline design, assuring sufficient safety against the burst limit state. A de-rated yield stress shall be used when designing pipelines for temperatures above 50 °C.

Stresses in Bends of Expansion Loops The axial stress and anchor reactions in buried pipe subjected to temperature differential may be estimated by assuming that the pipe is sufficiently long for the pipe/soil friction to fully restrain the pipe. In this case, the buried pipe is described as “fully restrained”. The maximum compressive thermal stress in a fully restrained pipe is calculated by:

c = E (T2 – T1) - h

Where, c = Maximum compressive thermal stress E = Modulus of elasticity of steel = Coefficient of thermal expansion of steel T2 = Maximum operating temperature T1 = Installation temperature

= Poisson’s ratio of steel h = Hoop stress due to internal pressure

Figure B8

Buried pipe bend

The axial load Fa in the pipe or the axial load at an anchor due to this temperature differential is: Fa = t A Where, Fa = The axial load in the pipe t = Compressive longitudinal stress due to temperature differential A = Metal cross section of pipe Since, the soil is not stiff, a hot pipe will tend to expand at pipe bends causing stresses at the bend.


Pipe-Soil Interaction

The soil resistance against pipeline movement is divided into two main sections, (a) Breakout section (b) Residual sections

The initial embedment of pipeline is calculated using Equation below:

Where, z = Initial penetration of pipe,

D =The pipe outside diameter, St = The soil sensitivity, V = Vertical load on the pipeline inclusive of dynamic load during pipeline

installation, Su = The undrained shear strength at bottom of the pipe.

The lateral breakout and residual resistances of soil may be calculated using the equation given below:

Where, = The submerged soil unit weight V = The vertical load on pipe Su_ID = Un-drained shear strength of soil at one pipe diameter below seabed. The Mobilization of breakout resistance is assumed within a pipe movement of less than half a diameter, while residual resistance occurs within 3 to 5 diameters.

Offshore Pipeline Systems - idc-online.com · 2019. 2. 4. · 48 Offshore Pipeline Systems...

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