Valves can be found just about anywhere today: in our homes, under the street, in commercial buildings and in thousands of places within power and water plants, paper mills, refineries, chemical plants and other industrial and infrastructure facilities.
The valve industry is truly broad-shouldered, with segments varying from water distribution to nuclear power to upstream and downstream oil and gas. Each of these end-user industries use some basic types of valves; however, the details of construction and materials are often very different. Here’s a sampling:
In the world of water distribution, the pressures are almost always relatively low and the temperatures ambient. Those two application facts allow a number of valve design elements that would not be found on more challenged equipment such as high- temperature steam valves. The ambient temperature of water service allows use of elastomers and rubber seals not suitable elsewhere. These soft materials allow water valves to be equipped to tightly seal off drips.
Another consideration in water service valves is choice in materials of construction. Cast and ductile irons are used extensively in water systems, especially large outside diameter lines. Very small lines can be handled quite well with bronze valve materials.
The pressures that most waterworks valves see are usually well below 200 psi. This means thicker- walled higher-pressure designs are not needed. That having been said, there are cases where water valves are built to handle higher pressures, up to around 300 psi. These applications are usually on long aqueducts close to the pressure source. Sometimes higher-pressure water valves also are found at the highest-pressure points in a tall dam.
The American Water Works Association (AWWA) has issued specifications covering many different types of valves and actuators used in waterworks applications.
The flip side of fresh potable water going into a facility or structure is the wastewater or sewer output. These lines collect all the waste fluid and solids and direct them to a sewage treatment plant. These treatment plants feature a lot of low pressure piping and valves to perform their “dirty work.” The requirements for wastewater valves in many cases is much more lenient than the requirements for clean water service. Iron gate and check valves are the most popular choices for this type of service. Standard valves in this service are built in accordance with AWWA specifications.
Most of the electric power generated in the United States is generated in steam plants using fossil-fuel and high-speed turbines. Peeling back the cover of a modern power plant would yield a view of high-pressure, high-temperature piping systems. These main lines are the most critical in the steam power generation process.
Gate valves remain a main choice for power plant on/off applications, although special purpose, Y-pattern globe valves are also found. High- performance, critical-service ball valves are gaining popularity with some power plant designers and are making inroads in this once linear-valve-dominated world.
Metallurgy is critical for valves in power applications, especially those operating in the supercritical or ultra-supercritical operating ranges of pressure and temperature. F91, F92, C12A, along with several Inconel and stainless-steel alloys are commonly used in today’s power plants. Pressure classes include 1500, 2500 and in some cases 4500. The modulating nature of peak power plants (those that operate only as needed) also puts a huge strain on valves and piping, requiring robust designs to handle the extreme combination of cycling, temperature and pressure.
In addition to the main steam valving, power plants are loaded with ancillary pipelines, populated by a myriad of gate, globe, check, butterfly and ball valves.
Nuclear power plants operate on the same steam/high-speed turbine principle. The primary difference is that in a nuclear power plant, the steam is created by heat from the fission process. Nuclear power plant valves are similar to their fossil-fueled cousins, except for their pedigree and the added requirement of absolute reliability. Nuclear valves are manufactured to extremely high standards, with the qualifying and inspection documentation filling hundreds of pages.
OIL AND GAS PRODUCTION
Oil and gas wells and production facilities are heavy users of valves, including many heavy-duty valves. Although gushers of oil spewing hundreds of feet in the air are no longer likely to occur, the image illustrates the potential pressure of underground oil and gas. This is why well heads or Christmas trees are placed at the top of a well’s long string of pipe. These assemblies, with their combination of valves and special fittings, are designed to handle pressures upwards of 10,000 psi. While rarely found on wells dug on land these days, the extreme high pressures are often found on deep offshore wells.
Wellhead equipment design is covered by API specifications such as 6A, Specification for Wellhead and Christmas Tree Equipment. The valves covered in 6A are designed for extremely high pressures but modest temperatures. Most Christmas trees contain gate valves and special globe valves called chokes. The chokes are used to regulate the flow from the well.
In addition to the wellheads themselves, many ancillary facilities populate an oil or gas field. Process equipment to pre-treat the oil or gas requires a number of valves. These valves are usually carbon steel rated for lower classes.
Occasionally, a highly corrosive fluid—hydrogen sulfide—is present in the raw petroleum stream. This material, also called sour gas, can be lethal. To beat the challenges of sour gas, special materials or material processing techniques in accordance with NACE International specification MR0175 must be followed.
The piping systems for offshore oil rigs and production facilities contain a multitude of valves built to many different specifications to handle the wide variety of flow control challenges. These facilities also contain various control system loops and pressure relief devices.
For oil production facilities, the arterial heart is the actual oil or gas recovery piping system. Although not always on the platform itself, many production systems use Christmas trees and piping systems that operate in the inhospitable depths of 10,000 feet or more. This production equipment is built to many exacting American Petroleum Institute (API) standards and referenced in several API Recommended Practices (RPs).
On most large oil platforms, additional processes are applied to the raw fluid coming from the wellhead. These include separating water from the hydrocarbons and separating gas and natural gas liquids from the fluid stream. These post-Christmas tree piping systems are generally built to American Society of Mechanical Engineers B31.3 piping codes with the valves designed in accordance with API valve specifications such as API 594, API 600, API 602, API 608 and API 609.
Some of these systems may also contain API 6D gate, ball and check valves. Since any pipelines on the platform or drill ship are internal to the facility, the strict requirements to use API 6D valves for pipelines do not apply. Although multiple valve types are used in these piping systems, the valve type of choice is the ball valve.
Although most pipelines are hidden from view, their presence is usually evident. Small signs stating “petroleum pipeline” are one obvious indicator of the presence of underground transportation piping. These pipelines are equipped with many important valves all along their length. Emergency pipeline shutoff valves are found at intervals as specified by standards, codes and laws. These valves serve the vital service of isolating a section of a pipeline in case of a leak or when maintenance is required.
Also scattered along a pipeline route are facilities where the line emerges from the ground and line access is available. These stations are the home for “pig” launching equipment, which consists of devices inserted into the pipelines either to inspect or clean the line. These pig launching stations usually contain several valves, either gate or ball types. All of the valves on a pipeline system must be full-port (full-opening) to allow for the passage of pigs.
Pipelines also need energy to combat the friction of the pipeline and maintain the pressure and flow of the line. Compressor or pumping stations that look like small versions of a process plant without the tall cracking towers are used. These stations are home to dozens of gate, ball and check pipeline valves.
The pipelines themselves are designed in accordance with various standards and codes, while pipeline valves follow API 6D Pipeline Valves.
There are also smaller pipelines that feed into houses and commercial structures. These lines provide water and gas and are guarded by shutoff valves.
Large municipalities, particularly in the northern part of the United States, provide steam for heating requirements of commercial customers. These steam supply lines are equipped with a variety of valves to control and regulate the steam supply. Although the fluid is steam, the pressures and temperatures are lower than those found in power plant steam generation. A variety of valve types are used in this service, although the venerable plug valve is still a popular choice.
REFINERY AND PETROCHEMICAL
Refinery valves account for more industrial valve usage than any other valve segment. Refineries are home to both corrosive fluids and in some cases, high temperatures.
These factors dictate how valves are built in accordance with API valve design specifications such as API 600 (gate valves), API 608 (ball valves) and API 594 (check valves). Because of the harsh service encountered by many of these valves, extra corrosion allowance is often needed. This allowance is manifested through greater wall thicknesses that are specified in the API design documents.
Virtually every major valve type can be found in abundance in a typical large refinery. The ubiquitous gate valve is still the king of the hill with the largest population, but quarter-turn valves are taking an increasingly large amount of their market share. The quarter-turn products making successful inroads in this industry (which was also once dominated by linear products) include high performance triple offset butterfly valves and metal-seated ball valves.
Standard gate, globe and check valves are still found en-masse, and because of the heartiness of their design and economy of manufacturing, will not disappear any time soon.
Pressure ratings for refinery valves run the gamut from Class 150 to Class 1500, with Class 300 the most popular.
Plain carbon steels, such as grade WCB (cast) and A-105 (forged) are the most popular materials specified and used in valves for refinery service. Many refining process applications push the upper temperature limits of plain carbon steels, and higher-temperature alloys are specified for these applications. The most popular of these are the chrome/moly steels such as 1-1/4% Cr, 2-1/4% Cr, 5% Cr and 9% Cr. Stainless steels and high-nickel alloys are also used in some particularly harsh refining processes.
The chemical industry is a big user of valves of all types and materials. From small batch plants to the huge petrochemical complexes found on the Gulf Coast, valves are a huge part of chemical process piping systems.
Most applications in chemical processes are lower in pressure than many refining processes and power generation. The most popular pressure classes for chemical plant valves and piping are Classes 150 and 300. Chemical plants have also been the biggest driver of the market share takeover that ball valves have wrestled from linear valves over the past 40 years. The resilient-seated ball valve, with its zero-leakage shutoff, is a perfect fit for many chemical plant applications. The compact size of the ball valve is a popular feature as well.
There are still some chemical plants and plant processes where linear valves are preferred. In these cases, the popular API 603-designed valves, with thinner walls and lighter weights, are usually the gate or globe valve of choice. Control of some chemicals is also effectively accomplished with diaphragm or pinch valves.
Because of the corrosive nature of many chemicals and chemical-making processes, material selection is critical. The defacto material is the 316/316L grade of austenitic stainless steel. This material works well to fight corrosion from a host of sometimes nasty fluids.
For some tougher corrosive applications, more protection is needed. Other high-performance grades of austenitic stainless steel, such 317, 347 and 321 are often chosen in these situations. Other alloys that are used from time to time to control chemical fluids include Monel, Alloy 20, Inconel and 17-4 PH.
LNG AND GAS SEPARATION
Both liquid natural gas (LNG) and the processes required for gas separation rely on extensive piping. These applications require valves that can operate at very low cryogenic temperatures. The LNG industry, which is growing rapidly in the United States, is continually looking to upgrade and improve the process of gas liquefaction. To this end, piping and valves have become much larger and pressure requirements have been raised.
This situation has required valve manufacturers to develop designs to meet tougher parameters. Quarter-turn ball and butterfly valves are popular for LNG service, with 316ss [stainless steel] the most popular material. ANSI Class 600 is the usual pressure ceiling for most LNG applications. Although quarter-turn products are the most popular valve types, gate, globe and check valves can be found in the plants as well.
Gas separation service involves dividing gas into its individual basic elements. For example, air separation methods yield nitrogen, oxygen, helium and other trace gases. The very low-temperature nature of the process means that many cryogenic valves are required.
Both LNG and gas separation plants have low-temperature valves that must remain operable in these cryogenic conditions. This means that the valve packing system must be elevated away from the low-temperature fluid through the use of a gas or condensing column. This gas column prevents the fluid from forming an ice ball around the packing area, which would prevent the valve stem from turning or rising.
Commercial buildings surround us but unless we pay close attention as they are built, we have little clue as to the multitude of fluid arteries hidden within their walls of masonry, glass and metal.
A common denominator in virtually every building is water. All these structures contain a variety of piping systems carrying many combinations of the hydrogen/oxygen compound in the form of potable fluids, wastewater, hot water, grey water and fire protection.
From a building survival standpoint, fire systems are most critical. Fire protection in buildings is almost universally fed and filled with clean water. For fire water systems to be effective, they must be reliable, have sufficient pressure and be conveniently located throughout the structure. These systems are designed to automatically energize in the case of fire.
High-rise buildings require the same water pressure service on the top floors as the bottom floors so high-pressure pumps and piping must be used to get the water upward. The piping systems are usually Class 300 or 600, depending upon building height. All types of valves are used in these applications; however, the valve designs must be approved by Underwriters Laboratories or Factory Mutual for fire main service.
The same classes and types of valves used for fire service valves are used for potable water distribution, although the approval process is not as strict.
Commercial air conditioning systems found in large business structures such as office buildings, hotels and hospitals are usually centralized. They have a large chiller unit or boiler to cool or heat fluid used for transferring cold or high temperature. These systems often must handle refrigerants such as R-134a, a hydro-fluorocarbon, or in the case of major heating systems, steam. Because of the compact size of butterfly and ball valves, these types have become popular in HVAC chiller systems.
On the steam side, some quarter-turn valves have made inroads in use, yet many plumbing engineers still rely on linear gate and globe valves, particularly if the piping requires butt-weld ends. For these moderate steam applications, steel has taken the place of cast iron because of steel’s weldability.
Some heating systems use hot water instead of steam as a transfer fluid. These systems are served well by bronze or iron valves. Quarter-turn resilient-seated ball and butterfly valves are very popular, although some linear designs are still used.
Although evidence of the valve applications mentioned in this article may not be viewable during a trip to Starbucks or to grandma’s house, some very important valves are always nearby. There are even valves in the engine of the car used to get to those places such as those in the carburetor that control the flow of fuel into the engine and those in the engine that control the flow of gasoline into the pistons and out again. And if those valves aren’t close enough to our everyday lives, consider the reality that our hearts beat regularly through four vital flow control devices.
This is just another example of the reality that: valves are truly everywhere. VM
Part II of this article covers additional industries where valves are used. Go to www.valvemagazine.com to read about pulp & paper, marine applications, dams and hydroelectric power, solar, iron and steel, aerospace, geothermal, and craft brewing and distilling.