The Britpipe

Pipeline Global Buckling

06.23

Global buckling of pipelines may be treated as the buckling of a bar (pipe) in compression. The global buckling may occur either downwards (free span), horizontally (lateral buckling on sea bed) or vertically (as upheaval buckling of buried pipelines or on a crest of exposed pipelines followed by a lateral turn-down). Local buckling is a gross deformation of the pipe cross section. Global buckling is a response to compressive force generated by high temperature and high pressure (HP/HT), which will generally reduce the axial capacity of the pipeline. Pipelines exposed to high temperature and high pressure or pipeline with a low buckling capacity will be governed by global buckling. In DNV’s RP-F110 [19], three global buckling scenarios resulted from HT/HP are introduced: · Exposed pipelines on even seabed. Global buckling occurs in the horizontal plane, post buckling configuration may be allowed. · Exposed pipelines in uneven seabed. Global buckling occurs first in the vertical plane (cause feed-in and uplift) and subsequently in the horizontal plane, or combined scenarios with scenario I, post buckling configuration may be allowed. · Buried/covered pipelines, global buckling in the vertical plane, so called upheaval buckling. Global buckling is a load response, not a failure mode. However, global buckling will imply some failure modes [20] such as: · Local buckling, for pipeline subjected to combined pressure. Longitudinal force and bending, local buckling may occur. The failure mode may be yielding of the cross section or buckling on the compressive side of the pipe. · Fracture, which is caused by tensile strain, generally includes brittle fracture and plastic collapse. · Fatigue, pipeline components such as riser, unsupported free spans, welding should be assessed for fatigue. Potential cyclic loading fatigue damages, which may include vortexinduced-vibrations (VIV), wave induced hydrodynamic loads, cyclic pressure and thermal expansion loads. · Ratcheting, ratcheting generally describes the accumulated plastic deformations under cyclic loads in pipelines that exposed to high temperature and high pressure. · Bursting, it is governed by tensile hoop stress, which may occur in the tensile part of pipeline.

Sumber

(http://www.diva-portal.org/smash/get/diva2:648750/FULLTEXT01.pdf)

Offshore Spiral Pipe

06.20

Spiral welded pipes market, though encountering overcapacity conditions particularly in North America, is expected to witness steady growth in the upcoming years driven by the implementation of new pipeline projects. Investments in oil and gas exploration and production, which are influenced by prevailing crude oil & gas prices, have a considerable impact on the demand for spiral welded pipes and tubes. Resurgent world economy and consequent increase in the demand for industrial natural gas is expected to drive up momentum of the spiral welded pipes market.

Global demand for spiral welded pipes, which are primarily used in the transportation of oil and gas and in water transportation projects, is closely linked to the investments in the energy sector. The energy sector makes use of spiral welded pipes with diameters of up to 60” and up to 80 feet in length. Another factor that is expected to fuel demand for spiral pipes and tubes is new pipeline construction activity due to the shift of population from traditional centers that would necessitate development of infrastructure for delivering oil and natural gas to the new locations. Demand for spiral welded pipes is also expected from the replacement market, as most of the existing pipeline infrastructure, particularly in developed regions, has reached their end of useful life. Structural applications of spiral welded pipes are also gaining momentum, specifically with additional activity occurring in port, offshore loading and infrastructure improvement sectors.

As stated by the new market research report on Spiral Welded Pipes and Tubes, Asia-Pacific represents the largest market worldwide, driven primarily by increased use in transporting natural gas. Besides Asia-Pacific, Latin America ranks among the fastest growing regional markets with compounded annual growth rate ranging between 7.5% and 9.0% over the review period. North American market, on the other hand, is encountering testing times owing to weak demand and overcapacity conditions. Oversupply is the major concern for spiral welded pipes market particularly with regard to large diameter double submerged arc welded or DSAW line pipes, which finds use in transmitting oil, natural gas liquids, and natural gas to consumers from drilling locations.

Despite the prevailing conditions, potential opportunities are expected primarily from the implementation of new pipeline projects in the upcoming years, resurgent growth of the US economy, and increased demand from natural gas exploration operations. Also, overcapacity conditions are expected to fade away in the coming years, as several megaprojects are set to be taken up across the world, particularly in regions such as Southeast Asia, Australia, Middle East, Africa, and West Asia.

Replacement of aging infrastructure offers huge potential for pipe manufacturers. The need to replace old pipelines is particular high in the US and Russia, where pipeline networks were mostly installed during the 60s and 70s. With the average lifespan of oil and gas transportation pipes ranging between 25 and 30 years, opportunities in the replacement market are huge, particularly for HSAW pipes. In the US, replacement demand holds enormous potential as a result of the recent enactment of the legislation that necessitates more inspections to be carried out, which could increase the likelihood of pipeline replacements. The Act is likely to play a critical role in enabling manufacturers of large diameter line pipes to survive the tough economic and overcapacity conditions.

Sumber:

(http://www.prweb.com/releases/spiral_welded_pipes_tubes/DSAW_HSAW_pipes/prweb10402550.htm)

Vortex Induced Vibration

06.18

Corrosion Prevention

06.13

Corrosion can be defined as the destruction or deterioration of a material because of reaction with its environment. Corrosion is a natural occurance and inevitable. Especially in seawater environment, corrosion is a threat for carbon steel pipe (offshore pipeline). Corrosion will damage pipeline and leads to pipe leak in which will be dangerous for the circumstances surround. Petroleum industry spends a million dollars per day to protect its pipelines. And so, there is urgency to protect and prevent pipeline from corrosion.

There are several methods that can be used to prevent and decrease the rate of corrosion on offshore pipeline. These methods are:

MATERIAL SELECTION

This method is just simply selecting the best and appropriate alloy carbon steel to a particular environment. For instance, the use of nickel-based alloy steel allows pipeline to withstand seawater environment without putting additional sacrificial anodes or impressed current, yet it’s far more expensive than having ordinary carbon steel with cathodic protected.

USE OF INHIBITOR

Sometimes corrosion in offshore pipeline attacked from inside (compounds brought by the fluid inside pipe e.g. sulphate). This can be helped by adding inhibitor. Inhibitor is a substance that when added in small concentrations to an environment, decreases the corrosion rate, such as chromate and nitrate.

CATHODIC PROTECTION

Cathodic protection is achieved by supplying electrons to the metal structure to be protected. Basically, cathodic protection has the pipeline become cathode, instead of anode, that way it won’t be corroded. There are two ways to cathodically protect a stucture. Firstly, Impressed Current Cathodic Protection (ICCP) and Sacrificial Anode Cathodic Protection (SACP).

1. Impressed Current Cathodic Protection (ICCP)

ICCP supplies electron by flowing electrical current from a power supply. This method is suitable for large structures regarding cost. For pipelines, anodes are arranged in groundbeds either distributed or in a deep vertical holes depending on several design and field condition factors including current distribution requirements.

2. Sacrificial Anode Cathodic Protection (SACP)

This method is also known as Galvanic Coupling. In the usual application, a galvanic anode, a piece of a more electrochemically “active” metal, is attached to the vulnerable metal surface where it is exposed to the corrosive liquid. Galvanic anodes are designed and selected to have a more “active” voltage (more negative electrochemical potential) than the metal of the target structure.

COATING

Relatively thin coatings of metallic and inorganic materials can provide a satisfactory barrier between metal and its environment. The chief function of such coatings is to provide an effective barrier.

Coating can be in the form of, for example, cladding. Cladding involves a surface layer of sheet metal put on by rolling two sheets of metal together. For instance, a nickel and a steel sheet are hot-rolled together to produce a composite sheet with, say, 1/8 inch of nickel and 1 inch of steel. This way the steel are protected with its environment since nickel is layered on the surface. Moreover, in the application for offshore pipeline, high density polyethylene(HDPE) and polypropylene layer can be coated on pipe bare surface. Both HDPE and polypropylene coating have low water permeation which will improve isolation of the pipe from seawater surrounds. Coating for pipeline is illustrated as below:

Sumber:

http://en.wikipedia.org/wiki/Cathodic_protection

http://met-engineering.blogspot.com

HSLA Steel

06.10

Pipeline Corrosion Resistance Alloy Material

06.09

Pipeline Stress Analysis

06.05

It is common practice worldwide that piping designers/layout personnel route pipes with consideration given mainly to space constraints, process and flow constraints (such as pressure drop) and other requirements arising from constructability, operability and reparability. Unfortunately, often pipe stress requirements are not sufficiently considered while routing and supporting piping systems, especially in providing adequate flexibility to absorb expansion/contraction of pipes due to thermal loads. So, when "as designed" piping systems are given to pipe stress engineers for analysis, they soon realize that the layout is "stiff" and suggest routing changes to make the layout more flexible. The piping designers, in turn, make routing changes and send the revised layout to the pipe stress engineers to check compliance again.

Such "back and forth" design iterations between layout and stress departments continue until a suitable layout and support scheme is arrived at, resulting in significant increase in project execution time, which, in turn, increases project costs.

This delay in project execution is further aggravated in recent years as operating pressures and temperatures are increased in operating plants to increase plant output; increased operating pressures increase pipe wall thickness, which, in turn, increase piping stiffness further; increased operating temperatures, applied on such "stiffer" systems, increase pipe thermal stresses and support loads. So, it is all the more important to make the piping layout flexible at the time of routing by piping designers.

The "Design by Color" product "checkSTRESS" from SST (different from CAEPIPE) for AutoCAD, CATIA, Autoplant, PDMS, Cadmatic, etc. can be used to substantially reduce the number of design iterations between the piping layout and stress departments, resulting in huge time savings during design.

Basic Pipe Stress Concepts for Piping Designers

Piping systems experience different loadings, categorized into three basic loading types, namely Sustained, Thermal and Occasional loads.

Sustained Load:

It mainly consists of internal pressure and dead-weight. Dead-weight is from weight of pipes, fittings, components such as valves, operating fluid, test fluid, insulation, cladding, lining etc.

Internal design/operating pressure develops uniform circumferential stresses in the pipe wall, based on which pipe wall thickness is determined during the process/P&ID stage of plant design such that "failure by rupture" is avoided. In addition, internal pressure develops axial stresses in the pipe wall. These axial pressure stresses vary only with pressure, pipe diameter and wall thickness, all three of which are pre-set at the P&ID stage and hence these axial pressure stresses cannot be reduced by changing the piping layout or the support scheme.

On the other hand, dead-weight causes the pipe to bend (generally downward) between supports and nozzles, producing axial stresses in the pipe wall (also called "bending stresses"); these bending stresses linearly vary across the pipe cross-section, being tensile at either the top or bottom surface and compressive at the other surface. If the piping system is not supported in the vertical direction (i.e., in the gravity direction) excepting at equipment nozzles, bending of the pipe due to dead-weight may develop excessive stresses in the pipe and impose large loads on equipment nozzles, thereby increasing the susceptibility to "failure by collapse".

Various international piping codes impose limits, also called "allowable stresses for sustained loads", on these axial stresses generated by dead-weight and pressure in order to avoid "failure by collapse".

For the calculated axial stresses to be below such allowable stresses for sustained loads, it may be necessary to support the piping system vertically. Typical vertical supports to carry dead-weight are:

a. Resting steel supports,

b. Rod hangers,

c. Variable spring hangers, and

d. Constant support hangers.

Both rod hangers and resting steel supports fully restrain downward pipe movement but permit pipe to lift up at such supports. If pipe lifts up at any of the rod hangers / resting supports during operating condition, then that support does not carry any pipe weight and hence will not serve its purpose.

Two examples are presented in this Tutorial to illustrate how piping can be supported by spring hangers and resting steel supports to comply with the code requirements for sustained loads.

Thermal Load (also referred as Expansion Load):

It refers to the "cyclic" thermal expansion/contraction of piping as the system goes from one thermal state to another thermal state (for example, from "shut-down" to "normal operations" and then back to "shut-down"). If the piping system is not restrained in the thermal growth/contraction directions (for example, in the axial direction of a straight pipe), then for such cyclic thermal load, the pipe expands/contracts freely; in this case, no internal forces, moments and resulting stresses and strains are generated in the piping.

On the other hand, if the pipe is "restrained" in the directions it wants to thermally deform (such as at equipment nozzles and pipe supports), such constraint on free thermal deformation generates cyclic thermal stresses and strains throughout the system as the system goes from one thermal state to another. When such calculated thermal stress ranges exceed the "allowable thermal stress range" specified by various international piping codes, then the system is susceptible to "failure by fatigue". So, in order to avoid "fatigue failure" due to cyclic thermal loads, the piping system should be made flexible (and not stiff). This is normally accomplished as follows:

a. Introduce bends/elbows in the layout, as bends/ elbows "ovalize" when bent by end-moments, which increases piping flexibility.

b. Introduce as much "offsets" as possible between equipment nozzles (which are normally modeled as anchors in pipe stress analysis).

For example, if two equipment nozzles (which are to be connected by a pipeline) are in line, then the straight pipe connecting these nozzles is "very stiff". On the other hand, if the two equipment are located with an "offset", then their nozzles will have to be connected by an "L-shaped" pipeline which includes a bend/elbow; such "L-shaped" pipeline is much more flexible than the straight pipeline mentioned above.

c. Introduce expansion loops (with each loop consisting of four bends/elbows) to absorb thermal growth/contraction.

d. Lastly, introduce expansion joints such as bellows, slip joints etc., if warranted.

In addition to generating thermal stress ranges in the piping system, cyclic thermal loads impose loads on static and rotating equipment nozzles. By following one or more of the steps from (a) to (d) above and steps (e) and (f) listed below, such nozzle loads can be reduced.

e. Introduce "axial restraints" (which restrain pipe in its axial direction) at appropriate locations such that thermal growth/contraction is directed away from equipment nozzles, especially critical ones.

f. Introduce "intermediate anchors" (which restrain pipe movement in the three translational and three rotational directions) at appropriate locations such that thermal deformation is absorbed by regions (such as expansion loops) away from equipment nozzles.

A few example layouts are presented below to illustrate how loops/offsets, axial restraints and intermediate anchors are used to reduce thermal stresses in piping (and resulting nozzle loads).

Occasional Load:

This type of load is imposed on piping by occasional events such as earthquake, wind etc. To protect piping from wind (which normally blows in horizontal plane), it is normal practice to attach "lateral supports" to piping systems. During an earthquake, the earth may also move vertically. To protect piping against both horizontal and vertical movement during earthquake, some of the resting supports may be made as "integral 2-way vertical and lateral restraints".

Fortunately, to carry sustained loads, normally vertical supports (as those listed under the Section titled "Sustained Load" above) are required. To withstand static seismic ‘g’ loads, "integral 2-way vertical and lateral restraints" are required. Generally, some of the vertical weight supports can be modified as "integral 2-way vertical and lateral restraints". On the other hand, for thermal loads, zero supports give zero stresses. So, thermal stresses and equipment nozzle loads will normally decrease as the number of supports goes down. Axial restraints and intermediate anchors are recommended only to direct thermal growth away from equipment nozzles.

Sumber:

(http://www.sstusa.com/pipe-stress-analysis-tutorial.php)

Linepipe Manufacture

06.03

The pipe-making process comprises three key processes: steel production, pipe manufacture and pipe coating. Within each of these steps, a number of processes are carried out to ensure the manufacture of high quality, functional pipe. BlueScope Steel, Orrcon Steel, OneSteel and Bredero Shaw have opened their factory doors to share the secrets of the pipe-making process with readers of The Australian Pipeliner.

Sourcing steel

The ingredients required for the production of line pipe steels come from all corners of Australia, with iron ore from Western Australia and South Australia, coal from the Illawarra and limestone from Marulan in New South Wales all brought to BlueScope Steel’s Port Kembla operation.

Before the production of steel can begin, high-quality iron – the basic ingredient for steelmaking – needs to be produced. The iron-making process is carefully controlled by blending various grades of iron ore to produce a mix which is exact in its content. Fines of iron ore and coal are also mixed and fused together in a sintering process to form a lumpy feed for charging into the blast furnace, and constitute approximately 60 per cent of the charge.

The last components of the reduction process are coke and limestone. Coke, a strong porous product, is formed by burning coal in ovens and is charged into the blast furnace to support the iron ore and sinter. It is coke which provides the carbon necessary for reducing the iron ore to iron. Limestone is used as a flux or cleaning agent in the reduction process.

These products are charged into either one of two blast furnaces, which are as tall as a 27 storey building and heated by the injection of air and gas to a temperature of 2,300 degrees Celsius. As the charge melts, the molten material makes its way to the bottom of the furnace where it is taken off and stored in refractory-lined ladles awaiting transfer to the next stage of production, where the liquid iron will be converted into steel at a production facility called the BOS or basic oxygen steelmaking.

Prior to this, there is one more important step which is key to the production of high-quality pipeline steel grades – the process of desulphurising the molten steel iron. Sulphur is an undesirable element in pipe steels as it reduces the cleanliness of the steel, decreases the ductility and restricts the weld properties of the final pipe. Once desulphurised, the molten iron is ready for conversion into steel.

In the BOS, iron is converted to steel around 50 times a day, and the Port Kembla operation produces in excess of 5 MMt/a of steel. In the process, the iron, which has a carbon content of around 4 per cent, is refined to levels of less than 1 per cent. It is this process that differentiates iron from steel. A vessel containing a mixture of approximately 300 t of charge, made up of 50 t of scrap and 250 t of iron from the blast furnace, is converted to steel by injection of pure oxygen, which creates a chemical reaction and increases the temperature to 1,700 degrees Celsius. Fluxes are added to absorb the impurities, the scrap melts and the carbon content is lowered to form steel.

The molten steel then moves to the vacuum degassing station where precise additions of the necessary alloys such as niobium, manganese, aluminium and titanium are made to meet the tight specification limits of pipe steels. Then, to further enhance the cleanliness of the steel, the molten steel is injected with a calcium silicide powder, which combines with some of the last remaining impurities and removes them from the molten steel. At this point the final chemical composition of the pipe steel grade is set and the molten steel is transferred to the slab casting facility.

In the slab caster, the steel is poured into a water-cooled mould and drawn through a series of segments, which chill the outer surface and slowly solidify the steel to a stage where it is fully hardened. The continuous strand of steel is then cut to length by automated gas torches to individually designed lengths or slabs. At this stage, the slab is approximately 12 m long and 230 mm thick.

After cooling, the slabs are inspected for any defects that may have been induced during the casting operation. Once the slabs have passed this quality assessment they move onto the final major processing stage where they are converted to a hot rolled strip to the exact dimensional and mechanical property requirements of the customer.

The purpose of rolling the cast slab is two-fold; firstly to achieve the final product dimensions and secondly to produce a finer grain structure; thereby giving the steel greater toughness and strength. In the Hot Strip Mill the slabs are reheated prior to rolling the steel down to its final desired thickness by passing it through a number of rolling stands. BlueScope Steel’s Port Kembla Hot Strip Mill uses six finishing stands to achieve the final desired strip thickness. The strip is then water-cooled on a long ‘run-out’ table prior to coiling. Precise control of slab reheating and rolling temperatures, scale removal, width and thickness ensure that the final strip meets all the dimensional, strength and toughness requirements of the ordered steel grade.

The steel coils are now allowed to cool before being strapped and labelled for despatch to the pipe manufacturing mills.

Producing pipe

Before steel is released from the steel mill, it is required by pipe manufacturers Orrcon Steel and OneSteel to have passed various quality tests, including: composition, strength, toughness, surface condition, and coil shape. When steel is despatched from the steel mill, a test certificate is also sent from the steel mill’s data system. When each coil arrives at these plants, checks are performed to ensure there has been no transport damage and that the identity of the coil matches its paperwork, markings and labels. Each coil is then unloaded into the warehouse, and its identity carefully recorded at OneSteel using a barcode process, or at Orrcon Steel using a traceability system called OrrTrace. The coil is then ready to be loaded onto a mill to make pipe.

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After identifying the coil, the key stages involved in the pipe making process include:

· Loading the coil into the mill;

· Forming;

· Welding;

· Cut-off;

· Bevelling;

· Hydrostatic testing;

· Ultrasonic inspection; and,

· Marking.

According to OneSteel Piping Systems Quality Assurance Manager Dr John Piper these are merely the manufacturing processes and much of the company’s effort is spent verifying the quality of each pipe as it is made via a multitude of test and inspection processes. These include visual inspection of the coils, weld visual monitoring, cooling process control, preliminary inspection of dimensions and surface quality, mill control ultrasonic testing, sampling for strength, composition and toughness testing, flattening and hydrostatic testing, and the final inspection process. This final process consists of ultrasonic testing, length and mass measurement, visual and dimensional inspection of the weld and body, and the bevel inspection. The outcome against the unique identity of each pipe is recorded to ensure that all pipe has passed all tests before being placed to order.

Orrcon Steel employs approximately 100 people at its Wollongong API Pipe Mill. This includes technical and quality, operations, administrative, maintenance, laboratory, logistics and other support staff. At OneSteel, the number of employees required at the plant is dependent on market demand and whether the company is running one, two or three shifts.

According to Mr Piper, the number of man hours required to make a pipe depends on the section and diameter, which range from 6–18 m in length and 168.3–508 mm in diameter. A production crew at the plant typically produces between 100 and 400 pipes per shift depending on the diameter, thickness, length and grade of the product being produced. Large diameter heavy wall pipe is produced at a slower rate than small diameter light wall pipe, however large diameter heavy wall pipe delivers a much higher output on a tonne per shift basis.

Orrcon Steel Technical Manager – Pipelines and Infrastructure Dr Cameron Dinnis says “Depending on the pipe size, the welding speed will be anywhere from 14–21m per minute. The pipe spends 10seconds at pressure during the hydrostatic test and will spend about one minute being ultrasonically tested. All of this means that the total man hours that go into a pipe can range between 1.5 and 5 hours.”

Welding the seam

As an electric resistance welded (ERW) pipe manufacturer, Orrcon Steel is essentially a manufacturer of weld seams.

To make the seam, the company uses a precise machine to trim the edges of the steel coil in a process known as edge milling, then heats the edges using high frequency electrical current and pushes them together to form the weld. The external and internal weld bead, which is the material that is ejected from the weld area when the strip edges are forced together, is then trimmed off by carbide cutting tools, leaving the weld seam flush with the surface of the pipe. The weld seam is then immediately subjected to an initial ultrasonic inspection. The seam is then heat-treated to ensure the microstructure is suitable for service. Following this, the pipe is tested to ensure that the weld seam and the pipe body have structural integrity and are within dimensional tolerances.

Specifically, the seam is subjected to a hydrostatic test and the full length of the weld seam is subjected to an ultrasonic inspection from both sides by 36 differently angled beams. The inspection frequency is such that a 0.5 mm long defect will be detected five times by each of the 36 angles in the time the ultrasonic probes traverse across it.

OneSteel achieves the weld seam using a similar process. “The integrity of the weld seam is of course, critical to the end use of the pipe so we are very careful in both process control and inspection,” says Mr Piper.

Sumber:

http://pipeliner.com.au/news/pipe_production_101/043584/

Christmas Tree

05.59

Christmas tree, or "tree" (not "wellhead" as sometimes incorrectly referred to), is an assembly of valves, spools, and fittings used for an oil well, gas well, water injection well, water disposal well, gas injection well, condensate well and other types of wells. It was named for its crude resemblance to a decorated tree.

Christmas trees are used on both surface and subsea wells. It is common to identify the type of tree as either "subsea tree" or "surface tree". Each of these classifications has a number of variations. Examples of subsea include conventional, dual bore, mono bore, TFL (through flow line), horizontal, mudline, mudline horizontal, side valve, and TBT (through-bore tree) trees. The deepest installed subsea tree is in the Gulf of Mexico at approximately 9,000 feet (2,700 m). (Current technical limits are up to around 3000 metres and working temperatures of -50°F to 350°F with a pressure of up to 15,000 psi.)

The primary function of a tree is to control the flow, usually oil or gas, out of the well. (A tree may also be used to control the injection of gas or water into a non-producing well in order to enhance production rates of oil from other wells.) When the well and facilities are ready to produce and receive oil or gas, tree valves are opened and the formation fluids are allowed to go through a flow line. This leads to a processing facility, storage depot and/or other pipeline eventually leading to a refinery or distribution center (for gas). Flow lines on subsea wells usually lead to a fixed or floating production platform or to a storage ship or barge, known as a floating storage offloading vessel (FSO), or floating processing unit (FPU), or floating production, storage and offloading vessel(FPSO).

A tree often provides numerous additional functions including chemical injection points, well intervention means, pressure relief means, monitoring points (such as pressure, temperature, corrosion, erosion, sand detection, flow rate, flow composition, valve and choke position feedback), and connection points for devices such as down hole pressure and temperature transducers (DHPT). On producing wells, chemicals or alcohols or oil distillates may be injected to preclude production problems (such as blockages).

Functionality may be extended further by using the control system on a subsea tree to monitor, measure, and react to sensor outputs on the tree or even down the well bore. The control system attached to the tree controls the downhole safety valve (SCSSV, DHSV, SSSV) while the tree acts as an attachment and conduit means of the control system to the downhole safety valve.

Tree complexity has increased over the last few decades. They are frequently manufactured from blocks of steel containing multiple valves rather than being assembled from individual flanged components. This is especially true in subsea applications where the resemblance to Christmas trees no longer exists given the frame and support systems into which the main valve block is integrated.

Note that a tree and wellhead are separate pieces of equipment not to be mistaken as the same piece. The Christmas tree is installed on top of the wellhead. A wellhead is used without a Christmas tree during drilling operations, and also for riser tie-back situations that later would have a tree installed at riser top. Wells being produced with rod pumps (pump jacks, nodding donkeys, and so on) frequently do not utilize any tree owing to no pressure-containment requirement.

Valves

Subsea and surface trees have a large variety of valve configurations and combinations of manual and/or actuated (hydraulic or pneumatic) valves. Examples are identified in API Specifications 6A and 17D.

A basic surface tree consists of two or three manual valves (usually gate valves because of their flow characteristics, i.e. low restriction to the flow of fluid when fully open).

A typical sophisticated surface tree will have at least four or five valves, normally arranged in a crucifix type pattern (hence the endurance of the term "Christmas tree"). The two lower valves are called the master valves (upper and lower respectively). Master valves are normally in the fully open position and are never opened or closed when the well is flowing (except in an emergency) to prevent erosion of the valve sealing surfaces. The lower master valve will normally be manually operated, while the upper master valve is often hydraulically actuated, allowing it to be used as a means of remotely shutting in the well in the event of emergency. An actuated wing valve is normally used to shut in the well when flowing, thus preserving the master valves for positive shut off for maintenance purposes. Hydraulic operated wing valves are usually built to be fail safe closed, meaning they require active hydraulic pressure to stay open. This feature means that if control fluid fails the well will automatically shut itself in without operator action.

The right hand valve is often called the flow wing valve or the production wing valve, because it is in the flowpath the hydrocarbons take to production facilities (or the path water or gas will take from production to the well in the case of injection wells).

The left hand valve is often called the kill wing valve (KWV). It is primarily used for injection of fluids such as corrosion inhibitors or methanol to prevent hydrate formation. In the North Sea, it is called the non-active side arm (NASA). It is typically manually operated.

The valve at the top is called the swab valve and lies in the path used for well interventions like wireline and coiled tubing. For such operations, a lubricator is rigged up onto the top of the tree and the wire or coil is lowered through the lubricator, past the swab valve and into the well. This valve is typically manually operated.

Some trees have a second swab valve, the two arranged one on top of the other. The intention is to allow rigging down equipment from the top of the tree with the well flowing while still preserving the Two-barrier rule. With only a single swab valve, the upper master valve is usually closed to act as the second barrier, forcing the well to be shut in for a day during rig down operations. However, avoiding delaying production for a day is usually too small a gain to be worth the extra expense of a having a Christmas tree with a second swab valve.

Subsea trees are available in either vertical or horizontal configurations with further speciality available such as dual bore, monobore, concentric, drill-through, mudline, guidlineless or guideline. Subsea trees may range in size and weight from a few tons to approximately 70 tons for high pressure, deepwater (>3000 feet) guidelineless applications. Subsea trees contain many additional valves and accessories compared to Surface trees. Typically a subsea tree would have a choke (permits control of flow), a flowline connection interface (hub, flange or other connection), subsea control interface (direct hydraulic, electro hydraulic, or electric) and sensors for gathering data such as pressure, temperature, sand flow, erosion, multiPhase flow, single phase flow such as water or gas.

Sumber:

https://en.wikipedia.org/wiki/Christmas_tree_(oil_well)

The Britpipe

Mengenai Saya

Arsip Blog

Pipeline Global Buckling

Offshore Spiral Pipe

Vortex Induced Vibration

VIV TYPES

Corrosion Prevention

MATERIAL SELECTION

USE OF INHIBITOR

CATHODIC PROTECTION

COATING

HSLA Steel

Pipeline Corrosion Resistance Alloy Material

Pipeline Stress Analysis

Basic Pipe Stress Concepts for Piping Designers

Linepipe Manufacture

Christmas Tree

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