Intro4u2u

<!– /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:”"; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:”Times New Roman”; mso-fareast-font-family:”Times New Roman”;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} –> Indonesia’s oil and gas regulator BPMIGAS has announced that oil and gas companies will soon be required to use domestic banks to finance their operations, according to the Jakarta Post Newspaper. BPMIGAS chairman R. Priyono said that the regulation could be put in place as soon as next month and would be mandatory for both national and foreign companies otherwise their expenses would not be reimbursed under the cost recovery scheme. According to Priyono the regulation aims to increase the liquidity of domestic banks as well as improving their balance of payments.

Significance: The announcement suggests that BPMIGAS is heeding the recommendation of the National Development Planning Board which last month suggested that local banks should support energy projects because the low percentage of non-performing loans to the energy sector made the risk of credit default relatively low(see Indonesia: 27 October 2008: Indonesian Energy Firms Encouraged to Seek Domestic Funding to Avoid Credit Crunch).At the end of August 2008 the energy sector only accounted for around US$4.2 billion or 3.5% of total domestic bank credits disbursed. Given that oil and gas companies are expected to spend US$11.8 million next year, the regulation would significantly increase domestic lending for energy projects. The government may be hoping that the regulation will encourage inter-bank lending, after the lowering of statutory reserve requirements for banks by 4% last month had a limited impact. However at the same time the move is likely to increase anxiety among foreign investors already worried about revisions in cost recovery mechanisms and Pertamina’s moves to acquire farm-in rights in large development projects. They may also be concerned about corruption in Indonesia’s banking sector following the successful prosecution of the Indonesian Central Bank’s former governor Burhanuddin Abdullah on charges of graft. If passed the regulation could deter investor-interest in 31 new oil and gas blocks due to be awarded in spring 2009.

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The Indian government awarded 44 oil and gas exploration blocks Thursday, with the maximum going to ONGC and its partners and first timers BHP Billiton-GVK Power, to attract US$1.5 billion investment in an attempt to cut reliance on imported energy.

Of the 45 blocks that received bids in the seventh round of auction under New Exploration Licensing Policy, the Cabinet Committee on Economic Affairs (CCEA) did not award a deepwater block in Mumbai basin to Cairn Energy India as it found the low bid by the sole bidder “detrimental to the government’s interest in future in terms of profit petroleum.”

Minister of State in Prime Minister’s Office Prithviraj Chauhan, briefing reporters on CCEA decision, said the production sharing contracts (PSCs) for the 44 block would be signed in a month.

A total of 57 blocks were offered in the auction but bids were received only for 45, with about US$1.49 billion minimum investment committed in exploration spend, Petroleum Secretary R S Pandey said.

ONGC and partners bagged the maximum number of 20 oil and gas exploration blocks offered by India in its largest ever international bid round that closed on June 30. First timers BHP Billiton and GVK Power emerged winners in seven deepsea blocks.

Reliance Industries forged an alliance with British Petroleum Plc but could manage only one Krishna-Godavari basin block.

Pandey said the government was considering bringing a next edition of bid round, NELP-VIII in February 2009. “Blocks are under finalisation and we hope to come out with NELP-VIII in February.”

Next acreage auction in Feb: Oil secy

The Indian government hopes to make its next offering of acreages for oil and gas prospecting in February, a top petroleum ministry official told TOI on Thursday after the Cabinet approved award of 44 concessions to winning bidders of the seventh round of exploration blocks’ auction.

“It is a big day for us (the government). Award of so many blocks have been cleared. The formal contracts can now be signed… within a month. It also now allows us to start work on the next round of acreage auctions… hopefully by February. The blocks are being carved and can be finalised,” petroleum secretary R S Pandey said.

The awarded exploration blocks envisage investments of at least $1.5 billion. While clearing these blocks, the Cabinet withheld the award of a deepwater block in Mumbai basin to Cairn Energy India as it found the low bid by the lone bidder “detrimental to the government’s interest in future in terms of profit petroleum”.

Among the awarded blocks, the maximum number was bagged by state-run ONGC and its partners and first-timers BHP Billiton-GVK Power. A total of 57 blocks were offered in the auction but bids were received only for 45. Of the 57 areas offered in NELP-VII, seven deepsea, two shallow water and three onland blocks did not receive any bid.

ONGC and partners bagged the maximum number of 20 oil and gas exploration blocks offered by India in its largest ever international bid round that closed on June 30. First timers BHP Billiton and GVK Power emerged winners in seven deepsea blocks. Reliance Industries forged an alliance with British Petroleum but could manage only one Krishna-Godavari basin block.

The Phase I investment commitment includes $321.15 million for exploration in deepsea, $598.255 million for exploration in shallow waters and $572.75 million for onland blocks, officials said. Besides seismic surveys, 141 exploration wells have been committed in the mandatory Phase I by the winning firms.

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Oil tumbled to a three-and-a-half year low below $49 a barrel on Friday, nearing a $100 drop from its July record high, as more distress for the global economy threatened to eat further into demand for fuels.

Asian stock markets dropped to a five-year low on Friday, tracking U.S. stocks that hit their lowest in a decade the previous session as the fate of the country’s major car makers continued to hang in the balance.

U.S. light crude for January delivery fell $1.02 to $48.40 a barrel at 0209 GMT, its sixth straight session of falls and a 14 percent drop for this week alone, heading for the largest weekly fall since early October.

London Brent crude shed 68 cents to $47.40 a barrel.

“The economy is pulling everything down like a black hole,” said Anthony Nunan, risk management executive at Tokyo-based Mitsubishi Corp. “Until the economy stabilises, it will be hard for oil to put in a bottom.”

Oil has lost two thirds of its value in just under four months since peaking above $147 in July, and is just above the lowest since May 2005 hit on Thursday.

Reflecting the sharp reversal in oil’s fortunes, Goldman Sachs, which in May had been talking of a $200 a barrel superspike, on Thursday again cut its 2009 forecast for U.S. crude oil to $80 a barrel from $86.

As demand tumbles, oil companies plan to store millions of barrels of crude in the hope economics will improve.

Shipping brokers said U.S. oil trader Koch and Royal Dutch Shell had booked supertankers capable of storing 10 million barrels of crude, more than top exporter Saudi Arabia produces in a day.

The further falls in oil prices brought more Organization of the Petroleum Exporting Countries members out in support of further output cuts.

Libya’s top oil official said the cartel may decide to reduce supply further at its informal meeting in Cairo next week if it finds members have implemented a previous decision to lower output.

The comments followed remarks from other OPEC members, including Kuwait, Iran and Venezuela, raising the possibility of a further cut in supply to prop up oil prices.

OPEC agreed in October to cut output by 1.5 million barrels per day, about 5 percent, from Nov. 1, but the move has failed to stem the decline in oil prices.

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THE boom in eastern Australia’s coal-seam gas industry will accelerate a rise in NSW gas prices, the national energy regulator says.

The State of the Energy Market 2008 report, to be published today, says the rush of projects to develop Queensland’s coal-seam gas into an exportable liquidate form has already nudged up prices along the east coast, as producers seek higher returns.

A gigajoule of gas fetched $2.50-$2.90 two years ago but the report’s lead essay by forecasters ACIL Tasman said recent sales in Queensland had peaked at $7.

Unlike electricity, gas markets outside of Victoria’s are opaque and allow deals to be settled privately, leaving forecasts hazy. But the report said gas was regularly selling for above $4 a gigajoule, as producers seek “significantly higher prices”.

Global oil powers have been attracted to converting Queensland’s extensive reserves into liquefied natural gas (LNG), which can fetch much higher prices on global markets. No LNG plants have been suggested for NSW but prices are being forced up regardless.

Oil has fallen more than 60 per cent from its peak but the companies behind the multibillion-dollar LNG projects are confident of getting high prices despite the downturn.

“The fact that most of the major [coal-seam gas] producers are currently looking to boost reserves and production capacity to underpin proposed LNG facilities means that the supply surplus which had prevailed in the Queensland market for several years has now been reversed,” it said.

Historically, Australians have had the world’s cheapest gas. In the US, it costs about $US6.70 per million British thermal units, slightly less than a gigajoule.

The chairman of the Australian Energy Regulator, Steve Edwell, said the carbon pollution reduction scheme would make gas more attractive. It emits less carbon than coal when burnt.

“It will add further momentum to the natural gas sector and over time will spur greater interest in clean coal and renewable generation technologies,” he said.

Gas companies have long argued that prices are set to rise towards “export parity’. The report confirms the Queensland LNG plans are accelerating the process.

Australia is the fifth largest LNG exporter. The coal-seam gas bonanza has seen the likes of ConocoPhillips in the US, Britain’s BG Group and Malaysia’s Petronas pay well above previous prices.

<!– /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:”"; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:”Times New Roman”; mso-fareast-font-family:”Times New Roman”;} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} –> A persistent shrinking in the market for petrochemical products is forcing Asian ethylene manufacturers to halt their cracker operations instead of just reducing production.

This month, Thailand’s IRPC Plc, formerly known as Thai Petrochemical Industry, stopped running its naphtha cracker, which is designed to produce 350,000 t/y of ethylene. This follows PTT Chemical’s suspension of a naphtha cracker with ethylene output capacity of 520,000 t/y that previously belonged to Thai Olefins Co. as well as an ethane cracker with ethylene output capacity of 400,000 t/y. Currently, only PTT Chemical’s ethane cracker able to make 460,000 t/y of ethylene, which previously belonged to National Petrochemical, is still operating in the country.

Taiwan’s Formosa Plastics expected to restart at the beginning of October its latest No.3 line with the capacity to produce 1.2 m t/y of ethylene after a routine maintenance shutdown begun at the end of August, but the new line, which was brought online in May 2007, is still not yet back in operation. The company plans to cease running its 735,000-t/y No.1 line and maintain the operating rate of its 1 mn-t/y No. 2 line at 80%.

In South Korea, Yeochun Naphtha Cracking Center is considering halting its 857,000-t/y No.1 line and 555,000-t/y No.2 line, and is likely to operate only its 400,000-t/y No.3 line. SK Energy had already suspended its superannuated No.1 line with the capacity to produce 200,000 t/y of ethylene.

Cracker operators in Japan, Singapore, Malaysia and Indonesia had previously been able to keep their operating rates at 80% or more, but the continued listlessness in demand for ethylene derivatives has compelled some to ratchet down their rates to 70%, a limit known as the “technical minimum.”

Crackers whose output mainly feed the manufacture of monoethylene glycol and styrene monomer, are finding it difficult to keep their operating rates above 70% and are likely to be obliged to put their operations on hold so as to limit losses.

An alloy is essentially a mixture of two or more elements, the principal component being a metallic element (the ‘parent metal’ or ’solvent’), so that the resultant mixture exhibits metallic properties. A wide variety of mechanical and physical properties may be obtained by alloying, so that alloys, rather than pure metals, are of the greatest importance for engineering.
If the constituent metallic atoms are chemically similar to one another, they will crystallise as a single set of crystals, since all the atoms will behave as if they belonged to the same species. A single-phase solid solution is then said to form, and its microstructure is often indistinguishable from that of a pure metal.
However, there may be a tendency for the elements to crystallise separately to form distinct and different crystals joined at mutual grain boundaries. Such a structure is an example of a phase mixture, which can usually be distinguished from a single-phase solid by metallographic examination.
Note that this could include the formation of an intermetallic compound. These compounds are in themselves of little practical value, since they tend to be hard and brittle, but they can be important as constituents of alloy systems.
1.3 Solid Solutions
Initially when a solid solution is formed the crystal structure is the same as that of the parent metal - the atoms of the solute or alloying element are distributed throughout each crystal, and a range of composition is possible. The solution may be formed in two ways:
(a) In substitutional solid solutions the atoms share a single common array of atomic sites (Fig 4a).
In some systems the parent metal will dissolve any proportion of the solute and retain its original crystal structure. However, in many cases there is a limited solubility and in order to accommodate a larger proportion of the added alloying element a change in the initial crystal structure becomes necessary to form a different solid solution, that is, another phase. In this way two solid solutions may exist together over a range of composition.
(b) In interstitial solid solutions the atoms of the solute element are small enough to fit into the spaces between the parent metal atoms, as illustrated (Fig 4b).
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(a) substitutional
(b) interstitial
Fig 4 The formation of solid solutions
Because of the atom size limitation, interstitial solid solutions are less common than substitutional solutions, although Carbon atoms can dissolve in iron crystals in this way in steel. Similarly Nitrogen can dissolve in steel and this is the basis of the Nitriding surface hardening process. The very small atoms of Hydrogen will dissolve interstitially in ferrous alloys, usually producing brittleness.
1.4 Phase Mixtures
A phase, present in an alloy as a separate entity, can be pure metal, a solid solution or an intermetallic compound. Any mixtures of two or more of these can occur. In binary systems, that is those of two elements, generally not more than two phases can exist together.
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2. EQUILIBRIUM DIAGRAMS
Thermal equilibrium (also known as Phase or Constitutional) diagrams are of great importance in metallurgy for with their aid it is possible to determine exactly the structure of a particular alloy at any given temperature, provided the alloy has been allowed to reach a state of equilibrium. Thus the phases present, their quantities and the chemical composition of each phase can be shown with precision. The diagrams are constructed principally by thermal analysis but also with microscopic studies, the examination of volume changes, X-ray diffraction and other techniques.
Equilibrium can be considered as a state of balance ultimately arrived at by the components at the temperature of the system concerned. However, in some cases such a state would take a very long time to be reached while in others it may never be reached at the temperature in question. For example, if an alloy is rapidly cooled by quenching to room temperature, chemical and physical changes may be suppressed such that they will never take place unless the alloy is reheated to allow them to occur. Very slow cooling must then follow.
2.1 Iron-Carbon Equilibrium Diagram (Fig 5)
Steel may be defined as an alloy of Iron and Carbon (up to about 1.7%C). Here it may be helpful to recall the allotropic nature of iron and that up to 910°C it has a body centred cubic crystalline form known as alpha α Iron, from 910°C-1400°C a face centred cubic structure, gamma γ Iron, reverting to body centred cubic delta δ. Iron above that temperature. These terms are modified in steel to Ferrite, Austenite and δ Ferrite. Other phases in the equilibrium structure are Cementite the inter-metallic compound Fe3C, and, Pearlite a phase mixture known as a Eutectoid consisting in this case of alternate layers of Cementite and Ferrite. Pearlite contains about 0.83%C.
Ferrite and δ Ferrite, the body centred cubic structures dissolve only very small amounts of carbon: less than 0.01% at room temperature. The face centred cubic Austenite however, is capable of dissolving up to nearly 2%C at 1150°C although this structure will change on reaching the Lower Critical Temperature 723°C below which the Eutectoid reaction will be complete. (Fig 6)
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Fig 5 The Iron-Carbon phase diagram
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Fig 6 Part of the Iron-Carbon Thermal-equilibrium diagram
Note that the Lower Critical Temperature 723°C below which all Austenite has been converted to Ferrite and Cementite is commonly known as the A1 temperature. The temperature above which the structure will be wholly Austenite, the Upper Critical Temperature, is known as the A3 temperature. Also the temperature above which the steel reverts to a wholly body centred cubic δ ferrite is known as the A4 temperature.
2.2 Slowly Cooled Structures
The most important reaction in steel is the decomposition of austenite on cooling. Consider the slow cooling of a steel of 0.83%C content (i.e. of the eutectoid composition) (Fig 7a); at 723°C the structure will transform to an eutectoid mixture consisting of alternate lamellae or plates of ferrite and cementite.
A steel of higher carbon content (known as a ‘hyper-eutectoid’ steel) (Fig 7b), 1.20%C, will remain austenitic down to the temperature around, say, 870°C at which the solvus line is crossed, so that Fe3C will start to be precipitated at the austenite grain boundaries.
Continued cooling and precipitation of cementite Fe3C will reduce the carbon content of the austenite until it reaches that of the eutectoid 0.83%C. When the temperature falls to below 723°C, this residual austenite will transform to pearlite, and the final microstructure will be cementite plus pearlite.
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A lower carbon steel (i.e. a ‘hypoeutectoid steel) of 0.4%C (Fig 7c) will begin to transform when the temperature falls below the solvus line by the precipitation of ferrite at the austenite grain boundaries.
Continued cooling and precipitation of ferrite will increase the carbon content of the austenite until it reaches that of the eutectoid 0.83%C. At 723°C this remaining austenite will transform to pearlite resulting in a final structure of ferrite plus pearlite.
2.3 Quenched Structures
The previous microstructures form in plain carbon steels which have been moderately slowly cooled (e.g. by cooling in air) from temperatures within the austenitic phase field, say from 50°C above the lower boundary line CED. This is called a ‘normalising’ heat treatment, but medium and high-carbon steels are very commonly subjected to more complex treatments in order fully to exploit their properties. These treatments involve, first, heating the alloy into the austenite phase field, as before, but then quenching it in water or brine which suppresses diffusion and thus the formation of ferrite and cementite. Under these conditions the austenite transforms by a process not involving diffusion into a metastable distorted form of body-centred iron known as ‘Martensite’ (Fig 7d). This process is extremely rapid and the transformation may be completed in a few microseconds.

All the carbon originally dissolved in the Austenite at high temperature remains after quenching in interstitial solution in the Martensite crystals. This has the effect of distorting the lattice from cubic to tetragonal symmetry. This lattice distortion by the dissolved carbon has the effect of hardening the structure and the resulting steels will not only be hard but brittle, for which there is little practical application. A second heat treatment called tempering is therefore required and this will reduce hardness and brittleness. If Martensitic steel is reheated to the temperature range 200-600°C (below the Austenite forming temperature) it rapidly decomposes to form body centred cubic ferrite and particles of Cementite.
This structure is on an extremely fine scale, the size of the carbide particles being dependent on the time and temperature of the treatment. The higher the temperature and the longer the time, the softer and less brittle the product.

HTML clipboardAngle Valve: A valve design in which one port is co-linear with the valve stem or actuator, and the other port is at a right angle to the valve stem. (See also Globe Valve.) Bellows Seal Bonnet: A bonnet that uses a bellows for sealing against leakage around the closure member stem (figure 1–6). Bonnet: The portion of the valve that contains the packing box and stem seal and can guide the stem. It provides the principal opening to the body cavity for assembly of internal parts or it can be an integral part of the valve body. It can also provide for the attachment of the actuator to the valve body.

Typical bonnets are bolted, threaded, welded, pressureseals, or integral with the body. (This term is often used in referring to the bonnet and its included packing parts. More properly, this group of component parts should be called the bonnet assembly.) Bonnet Assembly: (Commonly Bonnet, more properly Bonnet Assembly): An assembly including the part through which a valve stem moves and a means for sealing against leakage along the stem. It usually provides a means for mounting the actuator and loading the packing assembly. Bottom Flange: A part that closes a valve body opening opposite the bonnet opening. It can include a guide bushing and/or serve to allow reversal of the valve action. Bushing: A device that supports and/ or guides moving parts such as valve stems.

Cage: A part of a valve trim that surrounds the closure member and can provide flow characterization and/or a seating surface. It also provides stability, guiding, balance, and alignment, and facilitates assembly of other parts of the valve trim. The walls of the cage contain openings that usually determine the flow characteristic of Chapter 1. Introduction to Control Valves 10 Figure 1-8. Characterized Cages for Globe-Style Valve Bodies W0958/IL W0959/IL W0957/IL   
 
 the control valve. Various cage styles are shown in figure 1-8. Closure Member: The movable part of the valve that is positioned in the flow path to modify the rate of flow through the valve. Closure Member Guide: That portion of a closure member that aligns its movement in either a cage, seat ring, bonnet, bottom flange, or any two of these. Cylinder: The chamber of a piston actuator in which the piston moves (figure 1-7). Cylinder Closure Seal: The sealing element at the connection of the piston actuator cylinder to the yoke. Diaphragm: A flexible, pressure responsive element that transmits force to the diaphragm plate and actuator stem. Diaphragm Actuator: A fluid powered device in which the fluid acts upon a flexible component, the diaphragm. Diaphragm Case: A housing, consisting of top and bottom section, used for supporting a diaphragm and establishing one or two pressure chambers. Diaphragm Plate: A plate concentric with the diaphragm for transmitting force to the actuator stem. Direct Actuator: A diaphragm actuator in which the actuator stem extends with increasing diaphragm pressure. Extension Bonnet: A bonnet with greater dimension between the packing box and bonnet flange for hot or cold service. Globe Valve: A valve with a linear motion closure member, one or more ports, and a body distinguished by a globular shaped cavity around the port region. Globe valves can be further classified as: two-way single-ported; two-way double-ported (figure 1-9); angle-style (figure 1-10); three-way (figure 1-11); unbalanced cage-guided (figure 1-3); and balance cage-guided (figure 1-12). Lower Valve Body: A half housing for internal valve parts having one flow connection. The seat ring is normally clamped between the upper valve body and the lower valve body in split valve constructions.

Offset Valve: A valve construction having inlet and outlet line connections on different planes but 180 degrees opposite each other. Packing Box (Assembly): The part of the bonnet assembly used to seal against leakage around the closure Chapter 1. Introduction to Control Valves 11 Figure 1-9. Reverse Double-Ported Globe-Style Valve Body W0467/IL Figure 1-10. Flanged Angle-Style Control Valve Body W0971/IL member stem. Included in the complete packing box assembly are various combinations of some or all of the following component parts: packing, packing follower, packing nut, lantern ring, packing spring, packing flange, packing flange studs or bolts, packing flange nuts, packing ring, packing wiper ring, felt wiper ring, belleville springs, anti-extrusion ring. Individual Figure 1-11. Three-Way Valve with Balanced Valve Plug W0665/IL Figure 1-12. Valve Body with Cage-Style Trim, Balanced Valve Plug, and Soft Seat W0992/IL packing parts are shown in figure 1-13. Piston: A movable pressure responsive element that transmits force to the piston actuator stem (figure 1-7). Piston Type Actuator: A fluid powered device in which the fluid acts upon a movable piston to provide motion to the actuator stem. Piston type actuators (figure 1-7) are classified as either double-acting, so that full power Chapter 1. Introduction to Control Valves 12 Figure 1-13. Comprehensive Packing Material Arrangements for Globe-Style Valve Bodies B2565 / IL LOCATION OF SACRIFICIAL ZINC WASHER, IF USED. 
  

 14A1849-E 1 12A7837-A 
  
 13A9775-E can be developed in either direction, or as spring-fail so that upon loss of supply power, the actuator moves the valve in the required direction of travel. Plug: A term frequently used to refer to the closure member. Port: The flow control orifice of a control valve. Retaining Ring: A split ring that is used to retain a separable flange on a valve body. Reverse Actuator: A diaphragm actuator in which the actuator stem retracts with increasing diaphragm pressure. Reverse actuators have a seal bushing (figure 1-4) installed in the upper end of the yoke to prevent leakage of the diaphragm pressure along the actuator stem. Rubber Boot: A protective device to prevent entrance of damaging foreign material into the piston actuator seal bushing. Seal Bushing: Top and bottom bushings that provide a means of sealing the piston actuator cylinder against leakage. Synthetic rubber O-rings are used in the bushings to seal the cylinder, the actuator stem, and the actuator stem extension (figure 1-7). Seat: The area of contact between the closure member and its mating surface that establishes valve shut-off. Seat Load: The net contact force between the closure member and seat with stated static conditions. In practice, the selection of an actuator for a given control valve will be based on how much force is required to overcome static, stem, and dynamic unbalance with an allowance made for seat load. Seat Ring: A part of the valve body assembly that provides a seating surface for the closure member and can provide part of the flow control orifice. Separable Flange: A flange that fits over a valve body flow connection. It is generally held in place by means of a retaining ring. Spring Adjustor: A fitting, usually threaded on the actuator stem or into

Chapter 1. Introduction to Control Valves 13 the yoke, to adjust the spring compression. Spring Seat: A plate to hold the spring in position and to provide a flat surface for the spring adjustor to contact. Static Unbalance: The net force produced on the valve stem by the fluid pressure acting on the closure member and stem with the fluid at rest and with stated pressure conditions. Stem Connector: The device that connects the actuator stem to the valve stem. Trim: The internal components of a valve that modulate the flow of the controlled fluid. In a globe valve body, trim would typically include closure member, seat ring, cage, stem, and stem pin. Trim, Soft-Seated: Valve trim with an elastomeric, plastic or other readily deformable material used either in the closure component or seat ring to provide tight shutoff with minimal actuator forces. Upper Valve Body: A half housing for internal valve parts and having one flow connection. It usually includes a means for sealing against leakage along the stem and provides a means for mounting the actuator on the split valve body. Valve Body: The main pressure boundary of the valve that also provides the pipe connecting ends, the fluid flow passageway, and supports the seating surfaces and the valve closure member. Among the most common valve body constructions are: a) single-ported valve bodies having one port and one valve plug; b) double-ported valve bodies having two ports and one valve plug; c) twoway valve bodies having two flow connections, one inlet and one outlet; d) three-way valve bodies having three flow connections, two of which can be inlets with one outlet (for converging or mixing flows), or one inlet and two outlets (for diverging or diverting flows). The term valve body, or even just body, frequently is used in referring to the valve body together with its bonnet assembly and included trim parts. More properly, this group of components should be called the valve body assembly. Valve Body Assembly (Commonly Valve Body or Valve, more properly Valve Body Assembly): An assembly of a valve, bonnet assembly, bottom flange (if used), and trim elements. The trim includes the closure member, which opens, closes, or partially obstructs one or more ports. Valve Plug: A term frequently interchanged with plug in reference to the closure member. Valve Stem: In a linear motion valve, the part that connects the actuator stem with the closure member. Yoke: The structure that rigidly connects the actuator power unit to the valve.

HTML clipboardLinear Characteristic*: An inherent flow characteristic that can be repreChapter 1. Introduction to Control Valves 5 sented by a straight line on a rectangular plot of flow coefficient (Cv) versus rated travel. Therefore equal increments of travel provide equal increments of flow coefficient, Cv (figure 1-2). Loop: (See Closed Loop.) Loop Gain: The combined gain of all the components in the loop when viewed in series around the loop. Sometimes referred to as open-loop gain. It must be clearly specified whether referring to the static loop gain or the dynamic loop gain at some frequency.

Manual Control: (See Open Loop.) Open Loop: The condition where the interconnection of process control components is interrupted such that information from the process variable is no longer fed back to the controller set point so that corrections to the process variable are no longer provided. This is typically accomplished by placing the controller in the manual operating position. Packing: A part of the valve assembly used to seal against leakage around the valve disk or stem. Positioner*: A position controller (servomechanism) that is mechanically connected to a moving part of a final control element or its actuator and that automatically adjusts its output to the actuator to maintain a desired position in proportion to the input signal. Process: All the combined elements in the control loop, except the controller. The process typically includes the control valve assembly, the pressure vessel or heat exchanger that is being controlled, as well as sensors, pumps, and transmitters.

Process Gain: The ratio of the change in the controlled process variable to a corresponding change in the output of the controller. Process Variability: A precise statistical measure of how tightly the process is being controlled about the set point. Process variability is defined in percent as typically (2s/m), where m is the set point or mean value of the measured process variable and s is the standard deviation of the process variable. Quick Opening Characteristic*:

An inherent flow characteristic in which a maximum flow coefficient is achieved with minimal closure member travel (figure 1-2). Relay: A device that acts as a power amplifier. It takes an electrical, pneumatic, or mechanical input signal and produces an output of a large volume flow of air or hydraulic fluid to the actuator. The relay can be an internal component of the positioner or a separate valve accessory. Resolution: The minimum possible change in input required to produce a detectable change in the output when no reversal of the input takes place.

Resolution is typically expressed as a percent of the input span. Response Time: Usually measured by a parameter that includes both dead time and time constant. (See T63, Dead Time, and Time Constant.) When applied to the valve, it includes the entire valve assembly. Second-Order: A term that refers to the dynamic relationship between the input and output of a device. A second- order system or device is one that has two energy storage devices that can transfer kinetic and potential energy back and forth between themselves, thus introducing the possibility of oscillatory behavior and overshoot. Sensor: A device that senses the value of the process variable and provides a corresponding output signal to a transmitter. The sensor can be an integral part of the transmitter, or it may be a separate component. Chapter 1. Introduction to Control Valves 6 Set Point: A reference value representing the desired value of the process variable being controlled. Shaft

Wind-Up: A phenomenon where one end of a valve shaft turns and the other does not. This typically occurs in rotary style valves where the actuator is connected to the valve closure member by a relatively long shaft. While seal friction in the valve holds one end of the shaft in place, rotation of the shaft at the actuator end is absorbed by twisting of the shaft until the actuator input transmits enough force to overcome the friction. Sizing (Valve): A systematic procedure designed to ensure the correct valve capacity for a set of specified process conditions. Stiction: (See Friction.) T63 (Tee-63): A measure of device response. It is measured by applying a small (usually 1-5%) step input to the system. T63 is measured from the time the step input is initiated to the time when the system output reaches 63% of the final steady-state value. It is the combined total of the system Dead Time (Td) and the system Time Constant (t). (See Dead Time and Time Constant.) Time Constant: A time parameter that normally applies to a first-order element. It is the time interval measured from the first detectable response of the system to a small (usually 0.25% - 5%) step input until the system output reaches 63% of its final steady-state value. (See T63.) When applied to an open-loop process, the time constant is usually designated as
(Tau). When applied to a closed-loop system, the time constant is usually designated as λ (Lambda). Transmitter: A device that senses the value of the process variable and transmits a corresponding output signal to the controller for comparison with the set point. Travel*: The movement of the closure member from the closed position to an intermediate or rated full open position. Travel Indicator: A pointer and scale used to externally show the position of the closure member typically with units of opening percent of travel or degrees of rotation. Trim*: The internal components of a valve that modulate the flow of the controlled fluid.

Valve: (See Control Valve Assembly.) Volume Booster: A stand-alone relay is often referred to as a volume booster or simply booster because it boosts, or amplifies, the volume of air supplied to the actuator. (See Relay.) Sliding-Stem Control Valve Terminology The following terminology applies to the physical and operating characteristics of standard sliding-stem control valves with diaphragm or piston actuators. Some of the terms, particularly those pertaining to actuators, are also appropriate for rotary-shaft control valves. Many of the definitions presented are in accordance with ISA S75.05,

Control Valve Terminology, although other popular terms are also included. Additional explanation is provided for some of the more complex terms. Component part names are called out on accompanying figures 1-3 through 1-6. Separate sections follow that define specific rotaryshaft control valve terminology, control valve functions and characteristics terminology, and other process control terminology. Actuator Spring: A spring, or group of springs, enclosed in the yoke or actuator casing that moves the actuator stem in a direction opposite to that created by diaphragm pressure.

HTML clipboardThe controller output (CO) is the input to the valve assembly and the process variable (PV) is the output as shown in figure 1-1. When the term Dead Band is used, it is essential that both the input and output variables are identified, and that any tests to measure dead band be under fully loaded conditions. Dead band is typically expressed as a percent of the input span. Dead Time: The time interval (Td) in which no response of the system is detected following a small (usually 0.25% - 5%) step input.

It is measured from the time the step input is initiated to the first detectable response of the system being tested. Dead Time can apply to a valve assembly or to the entire process. (See T63.) Disk: A valve trim element used to modulate the flow rate with either linear or rotary motion. Can also be referred to as a valve plug or closure member.

Equal Percentage Characteristic*: An inherent flow characteristic that, for equal increments of rated travel, will ideally give equal percentage changes of the flow coefficient (Cv) (figure 1-2). Final Control Element: The device that implements the control strategy determined by the output of the controller. While the final control element can be a damper, a variable speed drive pump, or an on-off switching device, the most common final control element in the process control industries is the control valve assembly. The control valve manipulates a flowing fluid, such as gasses, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. First-Order: A term that refers to the dynamic relationship between the input and output of a device. A first-order system or device is one that has only one energy storage device and whose dynamic transient relationship between the input and output is characterized by an exponential behavior. Friction: A force that tends to oppose the relative motion between two surfaces that are in contact with each other. The friction force is a function of the normal force holding these two surfaces together and the characteristic nature of the two surfaces. Friction has two components: static friction and dynamic friction. Static friction is the force that must be overcome before there is any relative motion between the two surfaces. Once relative movement has begun, dynamic friction is the force that must be overcome to maintain the relative motion. Running or sliding friction are colloquial terms that are sometimes used to describe dynamic friction. Stick/slip or “stiction” are colloquial terms that are sometimes used to describe static friction. Static friction is one of the major causes of dead band in a valve assembly. Gain: An all-purpose term that can be used in many situations. In its most general sense, gain is the ratio of the magnitude of the output change of a given system or device to the magnitude of the input change that caused the output change. Gain has two components: static gain and dynamic gain. Static gain is the gain relationship between the input and output and is an indicator of the ease with which the input can initiate a change in the Chapter 1. Introduction to Control Valves 4 Figure 1-2. Inherent Valve Characteristics A3449/IL output when the system or device is in a steady-state condition. Sensitivity is sometimes used to mean static gain. Dynamic gain is the gain relationship between the input and output when the system is in a state of movement or flux. Dynamic gain is a function of frequency or rate of change of the input. Hysteresis*:

The maximum difference in output value for any single input value during a calibration cycle, excluding errors due to dead band. Inherent Characteristic*: The relationship between the flow coefficient and the closure member (disk) travel as it is moved from the closed position to rated travel with constant pressure drop across the valve. Typically these characteristics are plotted on a curve where the horizontal axis is labeled in percent travel and the vertical axis is labeled as percent flow (or Cv) (figure 1-2). Because valve flow is a function of both the valve travel and the pressure drop across the valve, conducting flow characteristic tests at a constant pressure drop provides a systematic way of comparing one valve characteristic design to another. Typical valve characteristics conducted in this manner are named Linear, Equal-Percentage, and Quick Opening (figure 1-2). Inherent Valve Gain: The magnitude ratio of the change in flow through the valve to the change in valve travel under conditions of constant pressure drop. Inherent valve gain is an inherent function of the valve design. It is equal to the slope of the inherent characteristic curve at any travel point and is a function of valve travel. Installed Characteristic*: The relationship between the flow rate and the closure member (disk) travel as it is moved from the closed position to rated travel as the pressure drop across the valve is influenced by the varying process conditions. (See Valve Type and Characterization in Chapter 2 for more details on how the installed characteristic is determined.) Installed Valve Gain: The magnitude ratio of the change in flow through the valve to the change in valve travel under actual process conditions. Installed valve gain is the valve gain relationship that occurs when the valve is installed in a specific system and the pressure drop is allowed to change naturally according to the dictates of the overall system. The installed valve gain is equal to the slope of the installed characteristic curve, and is a function of valve travel.

(See Valve Type and Characterization in Chapter 2 for more details on how the installed gain is determined.) I/P: Shorthand for current-to-pressure (I-to-P). Typically applied to input transducer modules. Linearity*: The closeness to which a curve relating to two variables approximates a straight line. (Linearity also means that the same straight line will apply for both upscale and downscale directions. Thus, dead band as defined above, would typically be considered a non-linearity.)

HTML clipboardWhat Is A Control Valve?

Process plants consist of hundreds, or even thousands, of control loops all networked together to produce a product to be offered for sale. Each of these control loops is designed to keep some important process variable such as pressure, flow, level, temperature, etc. within a required operating range to ensure the quality of the end product. Each of these loops receives and internally creates disturbances that detrimentally affect the process variable, and interaction from other loops in the network provides disturbances that influence the process variable.

To reduce the effect of these load disturbances, sensors and transmitters collect information about the process variable and its relationship to some desired set point. A controller then processes this information and decides what must be done to get the process variable back to where it should be after a load disturbance occurs. When all the measuring, comparing, and calculating are done, some type of final control element must implement the strategy selected by the controller. The most common final control element in the process control industries is the control valve.

The control valve manipulates a flowing fluid, such as gas, steam, water, or chemical compounds, to compensate for the load disturbance and keep the regulated process variable as close as possible to the desired set point. Many people who talk about control valves or valves are really referring to a control valve assembly. The control valve assembly typically consists of the valve body, the internal trim parts, an actuator to provide the motive power to operate the valve, and a variety Chapter 1. Introduction to Control Valves 2 of additional valve accessories, which can include positioners, transducers, supply pressure regulators, manual operators, snubbers, or limit switches. Other chapters of this handbook supply more detail about each of these control valve assembly components. Whether it is called a valve, control valve or a control valve assembly, is not as important as recognizing that the control valve is a critical part of the control loop. It is not accurate to say that the control valve is the most important part of the loop. It is useful to think of a control loop as an instrumentation chain. Like any other chain, the whole chain is only as good as its weakest link. It is important to ensure that the control valve is not the weakest link. Following are definitions for process control, sliding-stem control valve, rotary-shaft control valve, and other control valve functions and characteristics terminology.

NOTE: Definitions with an asterisk (*) are from the ISA Control Valve Terminology draft standard S75.05 dated October, 1996, used with permission. Process Control Terminology Accessory: A device that is mounted on the actuator to complement the actuator’s function and make it a complete operating unit. Examples include positioners, supply pressure regulators, solenoids, and limit switches. Actuator*: A pneumatic, hydraulic, or electrically powered device that supplies force and motion to open or close a valve. Actuator Assembly: An actuator, including all the pertinent accessories that make it a complete operating unit. Backlash: The general name given to a form of dead band that results from a temporary discontinuity between the input and output of a device when the input of the device changes direction. Slack, or looseness of a mechanical connection is a typical example. Capacity* (Valve): The rate of flow through a valve under stated conditions.

Closed Loop: The interconnection of process control components such that information regarding the process variable is continuously fed back to the controller set point to provide continuous, automatic corrections to the process variable. Controller: A device that operates automatically by use of some established algorithm to regulate a controlled variable. The controller input receives information about the status of the process variable and then provides an appropriate output signal to the final control element. Control Loop: (See Closed Loop.) Control Range: The range of valve travel over which a control valve can maintain the installed valve gain between the normalized values of 0.5 and 2.0. Control Valve: (See Control Valve Assembly.) Control Valve Assembly: Includes all components normally mounted on the valve: the valve body assembly, actuator, positioner, air sets, transducers, limit switches, etc. Dead Band: The range through which an input signal can be varied, upon reversal of direction, without initiating an observable change in the output signal. Dead band is the name given to a general phenomenon that can apply to any device. For the valve