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SOLUTIONS FOR FLUIDS, POWDERS & DRY BULK SOLIDS HANDLING | ORIFICE SLIDE GATE VALVE | DIVERTER VALVE | IRIS VALVE | LOSS IN WEIGHT GRAVIMETRIC FEEDER | VOLUMETRIC FEEDER | PELLET SCREENING & SORTING SYSTEM | KNIFE GATE VALVE | ECCENTRIC PLUG VALVE | PINCH VALVE | ABRASIVE SLURRY VALVE | SEVERE DUTY GLOBE CONTROL VALVE
Saturday, 31 December 2011
KEMROCK ends JV with German Co
Wednesday, 7 December 2011
India : An emerging market for specialty chemicals
Sunday, 4 December 2011
Rice Lake Weighing System expands in India
According to CEO Mark Johnson, many RLWS products are already sold overseas. "Our hope is to take advantage of a rapidly growing marketplace in India and use it to expand our brand recognition internationally," he explains.
In 2004, RLWS acquired Alabama-based Powell Scale, strengthening truck scale manufacturing and distribution within North America. Similarly, RLWS will rely heavily on the India partnership to expand distribution within Asia, Africa, and the Middle East.
Founded in 1982, SWSL is known throughout India for the manufacturing and distribution of railroad scales, truck scales, and other process control and material handling equipment for the aggregate, cement, and mining industries. RLWS chief operations officer Steve Parkman is optimistic about the joint venture. "Our new partner has about 85 employees and an established reputation for quality and customer service," he says. "We're looking forward to working with them. This is a good move for both of us."
Future plans include the construction of a new state-of-the-art facility in India. RLWS personnel will travel there to help ease the transition—providing technology, marketing, and product support. The joint venture is not expected to impact domestic manufacturing operations for RLWS.
Rice Lake Weighing Systems is a family-owned, ISO 9001 certified corporation, with headquarters, metrology laboratory, and main manufacturing plant in Rice Lake, WI. Additional manufacturing facilities are located in Jasper, AL and Newtown, CT. For more information, visit www.ricelake.com.
Gain-in-Weight vs. Loss-in-Weight Batching Systems
When determining whether a gain-in-weight or loss-in-weight system is best for your applications, the first step, I believe, is to recognize that this is a complex decision with roughly a dozen factors to consider—and each of these factors impact all the others. It is one of the most complex determinations involved with spec'ing a batching system.
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| A gain-in-weight system |
That said, the first step is to clarify priorities. Gain-in-weight is slower, but more accurate, since you are weighing only the amount discharged and only one product at a time on each scale. Loss-in-weight is faster, since you can discharge all the products at the same time, but it is less accurate.
Loss-in-weight allows you to discharge several ingredients simultaneously, but you need to monitor the weight of the discharging vessel. Most scales have a range of 10,000 increments that must cover the total material to be weighed. Thus, a 10,000-lb holding vessel can be weighed out in loss-in-weight mode in ±1 lb readout. If your discharge requires ±0.1 lb accuracy, of course, that option is not workable.
Other considerations include location, size of batch, time of batch, type of material, vibration in the area, sanitation requirements, clean-out, and cost. Finally, whether you are building a new facility, or retrofitting a plant that is running at full capacity has some bearing on which choice will best serve your needs. Let me offer a few thoughts on a few of these considerations.
If batches are small, you are likely more concerned with accuracy, so gain-in-weight is preferable. Regarding the type of material, if it is pharmaceutical grade, accuracy is critical, so again, gain-in-weight is the better option.
Is there vibration in the area? There are more load cells in a loss-in-weight system, and just one set in a gain-in-weight system. So, if there is vibration—a common condition—loss-in-weight may be preferable, all else being equal. Of course, the higher the batch weight, the less important vibration becomes.
Regarding sanitation, if you have to disassemble equipment for cleaning, as is the case with pharma and food products, gain-in-weight systems are much easier to manage.
Is the number of ingredients you are batching always the same? If batches are small and the recipe changes, you need to strike a balance between accuracy and speed. Two or three ingredients in a 4000-lb recipe? That's a situation ideal for loss-in-weight, unless accuracy requirements are extreme. Need high accuracy? Gain-in-weight will produce a better result. Need high production speeds? Loss-in-weight will almost always be the better choice, but there can be a balance between the two types of systems.
The new vs. existing facility question primarily relates to available space, and whether the material will originate in paper bags, silos, or bulk bags.
To summarize, gain-in-weight is more accurate and more controllable than loss-in-weight, just a little slower, although you can accelerate production speed by producing multiple batches simultaneously, even when recipes differ. If you have the luxury of flexibility—if you're building a new plant, for instance—this can be an incredibly efficient option.
Scott Culshaw is president and founder of Ingredient Masters (Cincinnati, OH), which provides custom-engineered solutions for dry ingredient handling and processing. For more information, e-mail sculshaw@ingredientmasters.com or visit www.ingredientmasters.com.
Selecting Right Dry Solid Feeder
Choosing the right dry-solids feeder for an application can be a challenging undertaking. Arming yourself with the necessary information can ease the task and ensure that the proper equipment selection is made.
Initially, system parameters must be carefully defined. This includes identifying the materials to be metered, their bulk densities, and their individual handling characteristics (whether they are free flowing, adhesive, cohesive, pressure sensitive, etc.). The feed-rate range (minimum, nominal, and maximum) must also be clarified. Before the proposed feeder is sized, consideration should be given to future feed-rate requirements. Accuracy requirements must also be established. This dictates whether a volumetric or loss-in-weight feeder is required for the application. As a system component, a feeder's performance can and will be affected by the other equipment in the system.
Careful consideration should be given to how the material will get to the feeder and to the type of device into which the feeder will discharge. For example, the feeder may be refilled manually, with a pneumatic conveyor, a mechanical conveyor, a live-bottom device (such as a vibratory bin bottom), or a static hopper. Such equipment can cause material fluidization, densification, or degradation, influencing product characteristics and feeder performance. In the discharge phase, the feeder may meter material into a conveyor, blender or mixer, extruder, or pneumatic system. Such devices can generate heat, positive or negative pressures, or moisture, all of which can affect feeder performance and end-product quality. An obviously crucial system parameter is feeder location. Also, equipment width, length, and height may be limited or restricted. And machine selection can be affected by the feeder environment (whether it is indoors, outdoors, temperature controlled, etc.).
Once prospective buyers have gathered all the necessary information, they can properly evaluate potential equipment suppliers. This step should start with a visit to several vendors. If possible, buyers should witness materials tests. All too often, feeders have a lower acquisition cost than other equipment. This factor, coupled with diminishing travel budgets and time constraints, results in vendor evaluations that are not as comprehensive as they should be. Testing product in a production-size piece of equipment (scaled-down tests are sometimes misleading) can prevent complications and production losses during installation. To ensure a proper comparison, test parameters such as equipment size, feed rate, sample duration, and refill frequency (for loss-in-weight feeders) should be the same for all manufacturers. Site visits can also give buyers insight into manufacturers' capabilities. They can be learning experiences—especially for buyers who are relatively new to the industry and to the process of selecting equipment.
During the evaluation stage, buyers should also address several other concerns: equipment reliability and versatility, warranties, maintenance and service requirements, and factory support—including whether the manufacturer offers parts and service 24/7. These are especially crucial concerns for production lines that operate around the clock, where downtime can cost thousands of dollars per hour.
Paul Matarazzo is senior mechanical engineer/manager in the materials testing facilities at Acrison Inc. (Moonachie, NJ). He also serves as an internal consultant on the selection and application of the company's range of dry-solids metering, hoppering, and blending equipment. An employee of the company for 31 years, he previously served as a project engineer and an applications engineer. Matarazzo is the coauthor of two international mechanical patents held by Acrison.
Selection Criteria for Material-Handling Valves
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Shawn Werner Selecting the correct slide gate or diverter valve for a conveying application is critical. Getting it wrong can mean the difference between system success and failure, especially when handling challenging materials. Several factors should be considered during the selection process, including material characteristics and their compatibility with valve seat and seal materials, conveying parameters, actuator requirements, valve maintenance, and environmental protection. Facilities should consider all of these factors to select the right valve for the application at hand. |
Material characteristics determine which type of valve is required. Coarse materials require valves and diverters with greater clearances, while fine materials such as carbon black, calcium carbonate, or titanium dioxide require valves and diverters with tighter tolerances in order to ensure dust-free service, prevent material leakage, and guarantee a clean plant environment. Other material characteristics that are important when selecting a valve are whether the material is sticky, abrasive, friable, corrosive, or a combination of these characteristics. To ensure maximum service life, appropriate seat and seal materials must be selected to handle a range of material characteristics.
Conveying parameters—whether the slide gate or diverter is used in a gravity or pressure installation—must also be considered when selecting a valve for a particular application. Material bridging in gravity applications presents a big challenge. While aeration or vibration can be used to improve material flowability, these techniques sometimes have undesirable consequences. Slide gates that are used to control material flow can be adversely affected by the use of these flow aids, especially if the slide gates are designed strictly for gravity applications. A common misconception is that if aeration pressure of 5 psig works, 25 psig will work even better. This is not the case. When using aeration, the overall goal is to infuse the material with air to enhance product flowability. This procedure should be followed using lower pressures over a longer period of time rather than higher pressures over a shorter period, achieving the same goal while minimizing the deleterious effects of aeration and maximizing slide gate service life.
When choosing a valve for material-handling applications, a key consideration is to select the appropriate actuator. The most common actuators include pneumatic cylinders and electric, hydraulic, and manual actuators. A facility should choose the appropriate actuator based on its initial cost, duty cycle, travel speed, and cycle frequency. Pneumatic cylinders are the most common actuators used for process valves. Clean and easy to maintain, they have a continuous-duty rating. Electric actuators are desirable in low-temperature applications, in which compressed air is vulnerable to freezing. The downside of using electric actuators is their slow actuation speeds, limited duty cycle, and high initial cost.
In fast-paced process environments, there is a premium on time. Hence, maintenance considerations should be a significant part of selecting a slide gate or diverter valve. Important factors to consider include service life, ease of maintenance, accessibility, the downtime required to rebuild a unit, and the cost of spare parts. More-demanding applications require frequent maintenance. In such cases, it is advantageous to use a slide gate or diverter that can be serviced easily or serviced while it is still installed. If minimal downtime is critical, a spare or campaign valve should be kept in reserve, enabling the plant to reduce downtime, increase production, and lower the stress on maintenance personnel.
The choice of materials used in the construction of slide gates, diverter valves, and seats and seals can affect the environment. For example, when valves are intended for outdoor use, nylon should not be used because of its water absorption characteristics. Materials that are resistant to corrosion such as aluminum and stainless steel should be used in place of carbon steel.
It is clear that many factors should be weighed before selecting a slide gate or diverter valve for a material-handling application. If a facility views each installation as unique, especially in challenging material applications, it will successfully choose the right valve, at the right price, with the right features.
Shawn Werner is chief engineer for Vortex Valves North America, a division of Salina Vortex Corp. Werner received a BS in mechanical engineering technology from Kansas State University. A member of the Society of Manufacturing Engineers, he has 15 years of experience in the dry bulk solids industry.
Flotech joins Valve Repair Council
Flotech, a leader in valve repair services in the US southeast, has joined the Valve Repair Council, an affiliate of the Valve Manufacturers Association of America. Flotech supports the mission of the valve repair council which advocates the original equipment manufacturer (OEM ) to repairing valves.
The proliferation of valve and actuator repair and rebuild shops around the country has led in some cases to facilities that operate without adequate quality control procedures, use substandard parts and do not have access to OEM specifications.
- To promote safety through proper repair and rebuild
- To establish and promulgate guidelines for proper repair and service
- To educate manufacturers, rebuilders and customers on the importance of proper service and the dangers inherent in substandard service
- To publish a list of members' qualified service facilities for the benefit of end-users
- To provide a forum for the legal exchange of information that will advance the quality and integrity of service
- To promote open discussion among OEMs, repair shops and users on problems relating to maintenance and repair
- To cooperate with standards' development bodies and regulatory agencies in the development of appropriate standards and regulations pertaining to service
Wednesday, 23 November 2011
Ball valve seats suit hot transfer
Ruhrpumpen launches magnetic driven centrifugal process pump
The pump is maintenance-free and meets the requirements of the TA-Luft (German Technical Instruction on Air Quality Control) and has a 100% leak-free performance, the company says, due to the magnet drive technology. By using a non-metallic containment shell, such as one made of zirconium oxide, magnetic losses are eliminated, increasing pump efficiency and great energy savings. The containment shell is designed for 40 bar (580 psi) at 120°C and can be used up to an operating temperature of 250°C (482°F). The magnets are made of thermally stable samarium cobalt material (Sm2Co17) and are suitable in standard for a maximum allowable operating temperature of 250°C (300°C). Special magnet drive systems for an operating temperature up to 450°C are available.
The central assembly of the magnetic drive system over the journal bearing avoids moment loadings on the journal bearing, thus avoiding eccentric loading of the inner magnet carrier during startup and shut-down.
There are more than 130 hydraulic combinations available for the SCE-M pump, and three different impellers for each pump size are available. The patent pending axial and double radial journal bearing made of sintered silicon carbide (SSiC) are available as standard.
Tuesday, 22 November 2011
Addressing Welding Procedures Not Covered by ASME Section IX
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Q: My customer has rejected my welding procedure specification (WPS) and has asked me to address items that are not required by ASME Section IX. Is this reasonable? A: Yes, this is a reasonable request. In many cases, it is a good idea to address items not covered by Section IX1. Many people view any given ASME code section as a handbook, and assume that if they follow everything in that code section, they have met all necessary requirements. However, each ASME code section has verbiage in the foreword warning the user that merely following the rules in that particular section will not ensure an adequate design. Such wording is phrased in ways like: "The user of the Code should refer to other pertinent codes, standards, laws, regulations or other relevant documents," and "it is not intended that this Section be used as a design handbook; rather, engineering judgment must be employed in the selection of those sets of Code rules suitable to any specific service or need." For example, Section IX does not impose enough controls to ensure reliable weld joints because it does not address the proper choice of filler materials. Section IX would allow welding nickel alloys or copper alloys together using carbon steel filler, provided the qualification specimen passed the appropriate mechanical tests. Many variables are not required to be addressed in a Section IX WPS. But in many of these cases, a WPS that does not address those variables may not produce consistently reliable weld joints or provide adequate guidance to the welder, both of which should be the primary purpose of the WPS. The following are examples of factors Section IX does not require, but that should be considered for inclusion in a WPS: 1. There are supplementary essential variables not required to be addressed for a WPS to be used on materials that are not impact-tested. One such essential variable is heat input, which is calculated based on current, voltage and travel speed. If heat input does not need to be addressed, Section IX does not require including voltage or travel speed values. Some of the software packages for creating WPS documents will even omit this information automatically. On the other hand, if no voltage or travel speed values are specified, it is possible to follow the WPS and still produce unacceptable welds. Therefore, even though not required by Section IX, it is beneficial to include reasonable voltage and travel speed values on the WPS—even for materials that are not impact-tested. 2. For a WPS that involves carbon and alloy steels postweld heat-treated (PWHT) below the lower transformation temperature (LTT), Section IX only requires the WPS to indicate the PWHT must be below the LTT. Most WPSs for non-impact-tested carbon steels and alloy steels will actually state a PWHT temperature, but many omit the tolerance on this temperature and any soak time requirements. To ensure that proper strength, ductility and hardness requirements are met, a PWHT temperature range should be stated on the WPS. That temperature range should be based upon the PWHT temperature used on the qualification coupon, taking into consideration the effects of higher and lower temperature on the strength, ductility, hardness and toughness of the material. In addition, as a function of base metal thickness, guidance should be provided regarding the soak time, as well as providing absolute minimum and maximum allowable soak times. Again, strength, ductility, hardness and toughness of the material should be taken into account. 3. Section IX does not prohibit combining procedures that have been qualified in different ways, such as procedures qualified with and without PWHT, or procedures qualified with and without controls required for impact-tested materials. In fact, creating one WPS that covers non-impact-tested material (such as WCC) and impact-tested material (such as LCC), with and without PWHT is both possible and allowed. These procedures are handy when it is necessary to get a customer review. However, the combined procedures tend to be difficult for welders to follow because they usually contain a number of notes and tables, and for any given job it can be hard to determine what information actually applies. Although the combined approach is allowed, and although the combined document might be convenient from a creation and maintenance standpoint, it is actually better to create four separate WPS documents (non-impact without PWHT, non-impact with PWHT, impact without PWHT and impact with PWHT), because each WPS will then convey much more clearly the specific requirements for the pertinent situation. In summary, although Section IX imposes an abundance of rules for qualifying and writing WPSs, there are many instances where additional controls and information need to be conveyed to ensure results that meet the intended requirements of the weld. Therefore, if your customer makes a comment on your welding procedure, view it as a possible learning experience. In the end, your WPSs will be better for it. |
Thursday, 10 November 2011
Upstream & Downstream Pipeline Valves
This nation is crisscrossed by hundreds of thousands of miles of crucial pipelines that transport vital feedstock from sources to the places where it's transformed into fuel and products. For the valve industry, that translates into millions of dollars of business.
According to Hart Data and Mapping Services, the United States has over 700,000 miles of crude oil and natural gas pipelines—about 100,000 miles of crude onshore pipelines and over 600,000 miles of onshore gas pipelines. This number stands to greatly increase as drilling in the various shale plays across the continent occurs. These seemingly endless strings of pipe have one thing in common: They all contain large numbers of valves optimized for pipeline operating conditions.
WHAT'S IN A PIPELINE?
Both quarter-turn and multi-turn block valves as well as check valves are used in pipeline service. Those built for gas or crude oil pipeline service are designed and tested in accordance with the American Petroleum Institute (API) specification 6D "Pipeline Valves." The document, which is also published by the International Organization for Standardization as ISO 14313, includes requirements for gate, ball, check and plug type valves. Prior to the mid-1950s, the choice of valve for use in pipeline blocking applications was easy—gate valves were used because the pipeline ball valve had not been invented yet. Some plug valves also were used back then, but the majority of the designs for these valves were reduced-port type that were not piggable.
The term "piggable" has nothing to do with breakfast meat choices. Rather, it means being "pig-capable"—in other words, the devices designed to clean or inspect the interior of the pipeline (the "pigs") also may be passed through the bore of the valve without catching on a reduced bore or other interior projection in the valve. A requirement in API 6D gate valves is that their inside bore dimensions are precisely specified to allow this passage of pigs.
With the advent of quality pipeline ball valves over the past few decades, sales of pipeline gate valves have fallen. Meanwhile, pipeline ball valves, which are trunnion style, are now making inroads in all types of pipeline service, particularly in natural gas. Still, holdouts exist.
"Some companies are staunchly entrenched in the gate valve," according to David Fehrenkamp, a senior sales engineer with Cameron. He also adds that "in many natural gas pipeline operations, quarter-turn has taken over 100%."
So why do many pipeline owners favor the gate valve for pipeline service? Product pipelines that carry fluids such as gasoline, distillates, diesel fuel and other finished petroleum products are a popular place for the rough and ready gate valve. "We use slab gate valves for most of our main line valves, but we do use expanding gate valves on our product line from Texas City to Pasadena," says Billy Daigle, maintenance services specialist for Marathon Pipe Line LLC (MPL). "We use expanding gate valves for station isolation valves and pig launchers. Pig launcher and receiver service is harder on valves because of the debris from the pigging operation, so we choose expanding gates because of their toughness," he adds.
Ball, check and manifold valves are commonly used in pipeline service.
The quarter-turn vs. gate valve debate gets hotter when cost becomes the prime factor for selection. The quarter-turn trunnion pipeline ball valve is much cheaper to make than the jumbo-sized gate valves, with their large and expensive body castings. Another factor that tips the pendulum toward quarter-turn pipeline valves is the availability and delivery of quarter-turn products. Because drilling in the shale plays across the country is exploding in terms of how fast it's occurring, Fehrenkamp says the requests from customers for delivery time is "rush, rush, rush, I need it now!" A domestically produced trunnion pipeline ball valve can be built in roughly four weeks, which is about the time needed to get a good gate valve casting under the luckiest of circumstances. An additional four to six weeks might then be required to complete the gate valve machining, assembly and testing.
Some explanation is in order when speaking of pipeline gate valves. Gate valves used in this service are different from the wedge-type gate valves common in the downstream petrochemical and refining industries. The pipeline gates come in two basic types: slab and expanding wedge. The slab type utilizes a large slab that floats slightly in the valve body and seals downstream with the aid of upstream pressure. Spring-loaded seats are often employed to increase the sealing efficiency. The expanding gate, on the other hand, uses a split-disc design and separator mechanism that tightly expands the gate both upstream and downstream as the valve is closed. This type then reverses the process upon opening. The tighter closing design enables the valve to seat more effectively at lower pressures.
A QUESTION OF INTEGRITY
Valve integrity along with pipeline integrity is of prime importance to the pipeline owner as well as those who live and work close to the line. A complex formula for risk assessment is used to guide pipeline operators with inspection programs. The assessment criteria include the product, age of the pipeline, and proximity to population centers, local housing and occupied structures. The pipeline itself must be inspected at specified intervals. This line inspection is usually performed by "smart pigs," complex devices that roll through the line to perform radiography, remote visual, ultrasonic evaluation and other inspections.
Pig launchers are hard on valves because of the debris from the pigging operation.Valves, on the other hand, need their own inspection programs. The U.S. Department of Transportation has developed natural gas pipeline valve inspection criteria detailed in CFR Title 49, part 192, "The Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards." Paragraph 192.745 of that title states, "Each transmission line valve that might be required during any emergency must be inspected and partially operated at intervals not exceeding 15 months, but at least once each calendar year." Similar requirements are published for crude oil and hazardous liquid pipelines in CFR Title 49, part 195, "Transportation of Hazardous Liquids by Pipeline," paragraph 195.420.
Proper valve maintenance is always vital, and pipeline valves are no exception. Since most pipeline valves have a seat sealant injection feature to facilitate tight closure, the sealant must be properly introduced into the seat seal area. New valves typically require more sealant top-off than those that have been in operation for a year or two.
Pipelines use a variety of valves to control fluids both above and below the ground.All pipeline operators have preventive maintenance (PM) and repair programs to ensure the life and functionality of their valves. Most companies will use a combination of in-situ repair along with shop refurbishments for tough repair cases. "We spend over 25% of our time in valve shops to get the valves just like we want them," says MPL's Daigle.
Because of the importance of proper pipeline valve repair, a specification that describes the repair procedure is in place: API 6DR, "Repair and Remanufacture of Pipeline Valves."
HOW PIPELINES WORK
Understanding how pipelines operate provides a better understanding of how valves are used in pipeline service. Major pipelines receive input from either smaller gathering lines, tank farms or, in the case of finished products, refineries and petrochemical plants. Because of friction losses, the arriving pressure of the fluid is much too low to provide enough energy to send the product very far through the line. Most transmission pipelines in the United States operate at maximum pressures of less than 1440 psi. Common maximum target pressures range from 700-725 psi and 1300-1400 psi, which equates to ANSI classes 300 and 600 respectively. These maximum pressures would only be found immediately downstream of pumps or compressors.
Because of the pressure drop in the line, booster pumping stations at intervals along the line are needed. In the case of a liquid such as crude oil, a minimum pressure of about 25-50 psi is needed for the suction side of the booster pumps to operate. Each booster pumping station is equipped with manifolds containing many valve types, including gate, ball, check, and in areas where pigging is not required, reduced port, lubricated plug valves. Additionally, control valves often are used to regulate flow from the stations.
The most common pressure class for pipeline transmission lines is class 600, which has a working pressure of 1440 psi. The valve ratings are in accordance with The American Society of Mechanical Engineers (ASME) standard B16.34 and API 6D.
Valves play a critical role in keeping the nation's pipelines safe.Although a number of valves are in operation at each pumping station (for liquids) or compressor station (for gas transmission), the critical valves in a pipeline are spaced along its route. They serve as blocking or isolation valves to segregate pipeline sections for required maintenance or to help in cases of an accident. The minimum required spacing of these valves is prescribed in ASME B31.4, "Gas Transmission & Distribution Piping Systems" and ASME B31.8, "Pipeline Transportation Systems for Liquid Hydrocarbons & Other Liquids."
Several factors influence valve spacing, including: 1) the amount of potential fluid leakage, 2) the impact of a release, 3) future development in the pipeline area, and 4) the time required to blow down (empty) an isolated section. Other criteria include how close the line is to occupied buildings and houses. According to B31.4, the distance between block valves could be as little as four miles apart for a gas pipeline.
Slab gate valves are used along the pipeline systems.Liquid pipelines have their own criteria for valve placement. They are placed: 1) at the suction end and discharge ends of a pump station, 2) on each line entering or leaving a storage tank area, 3) on each mainline at locations along the pipeline that will limit damage or pollution from accidental hazardous liquid discharge, 4) on each lateral take-off from the trunk line, 5) on each side of a water crossing that is more than a 100 feet wide, and 6) on each side of a reservoir holding water for human consumption.
Additionally, check valves may be installed on grades and the downstream side of rivers and streams for more protection from backflow conditions in case of a line breach.
Many block valve installations are outfitted with automatic shutdown controls. These controls are set to close the valve if pressure or flow rates change, indicating a possible breach in the line. By having these valves spaced throughout the line, the amount of potential fluid leakage that might occur during a line break is limited. Additionally, many pipeline valves are designated as emergency shutdown valves (ESD), which are remotely operated from the pipeline control center.
These block valve location requirements account for the numerous small, fenced-in valve installations visible when driving around areas with many pipelines—numerous pipeline block valves are located above the ground for easy maintenance. However, some are buried, with only the operating mechanism and auxiliary lubrication and bleed lines showing. These installation areas used to be the exclusive domain of gate valves. However, today welded body trunnion-mounted ball valves are very popular, especially for clean natural gas transmission lines. The unique welded body construction eliminates the potential body-bonnet leak path, while the only remaining leak path is up through the packing area.
Though fugitive emissions (FE) leakage has been a focal point in the refining industry for over 20 years, the upstream and midstream markets have been fairly immune from FE scrutiny. However, that situation is changing. According to MPL's Daigle, "LDAR [leak detection and repair] for pipelines is becoming popular and required, especially since packing leaks are the most common leaks we deal with."
One place where emissions of any type are unacceptable to almost everyone is in undersea pipelines. Because they are surrounded by water and vibrant marine life, undersea pipelines certainly have their own set of challenges. However, there are other key differences from on-land pipelines that affect design, including the design of the valves attached to the pipelines.
For example, undersea pipelines that connect wellheads to gathering points often operate at much higher pressures than their onshore counterparts. It is not uncommon for these lines to see 10,000 psi. Valves designed for this submerged service are critical, purpose-built flow control devices that absolutely must work properly when called upon to operate. Because of the unique undersea environment, standard API 6D requirements are not deemed tough enough, so a special underwater valve specification was written to cover these products: API 6DSS "Specification for Subsea Pipeline Valves."
TESTING
Although interior pressures are also quite high in subsea pipelines, it is sometimes the outside pressure from the extreme depths that introduces the most stress on valves and piping. As a result, pipeline valves designed for installation at great depths are often tested in a hyperbaric chamber, where extreme pressure is exerted on the outside of the valve, while the inside is sealed against the external pressure.
All pipeline valves receive seat and shell tests per API 6D or 6DSS, not unlike their downstream counterparts, which are usually tested in accordance with API 598, "Valve Inspection & Testing." One difference between the two testing documents is that, with API 6D pipeline valves, the holding times for the tests are much longer. For example, a 24-inch valve shell tested per API 598 requires a five-minute duration, while the same size valve tested per API 6D requires a 30-minute duration. These longer holding times for pipeline valve tests are often extended into hours by the supplementary test requirements of many pipeline owners.
While pipelines and pipeline valves lie mostly invisible beneath six feet of earth or under 600 feet of ocean, they are nonetheless highly "visible" when an accident occurs. As a result, pipeline valves are closely scrutinized members of the valve family. They are built to tougher standards and must work every time because they must protect lives and property that lie near their installations. Pipeline valves could borrow the Latin motto of the United States Coast Guard, which is "Semper Paratus," which means: always ready.