Author:Site Editor Publish Time: 2018-08-29 Origin:Site
The valve industry is truly broad and diverse; valves are found in our homes, our offices, under our streets and in all our factories and plants.
PULP & PAPER
Although the pulp and paper industry is not as extensive as it used to be, the products are still in demand, and mills remain filled with many valves. Some of the service conditions in a paper mill can be very harsh because of the corrosive nature of various processes. This means valve material selection is critical. The typical paper mill used to rely strongly on 316ss [stainless steel] material for valve construction. However, today's closed loop systems include other impurities into the fluid stream, such as chlorides, which makes standard 316ss less suitable. Nickel alloys as well as higher grade stainless steels are specified more and more for paper mill service.
Pulp and paper mills also contain slurry lines that require special valves. The design of choice in these applications is the knife gate, with its sharp, thin cutting edge, which can cut through the slurry solids. Like other complex process plants, virtually every type of valve can be found in a pulp and paper mill. Since the industry is running on tighter margins these days, total cost of ownership is important to plant owners. Because of this, pulp and paper mills are strong users of valve repair to increase returns on investment.
Marine valves perform many different duties both above and below the decks of the ships. All vessels need some form of energy to power their engines, and valves regulate the loading and storage of whatever is used. A diesel tugboat might have only one fuel valve, while a large cargo ship may have a complicated system of pumps and manifolds with multiple valves directing the fuel to various tanks on the ship. Oftentimes, these tanks are located at strategic points to aid in the ballasting of the vessel.
Also vital to ships is water ballast and bilge systems. These systems may use piping and valves of hand-held size or the equipment can be as large as NPS 30. Valves handling seawater must be hearty and designed to withstand the rigors of the harsh environment. Firefighting piping systems are important in ships as well since no local fire departments could be called if an emergency at sea occurs.
Today's ships and barges are home to virtually every type of modern valve, not just the old school gate, globe and check valve. Ball valve is increasingly popular, including the metal-seated types. However, the valve that has probably made more recent inroads in the previously gate-valve-dominated marine industry is the lined butterfly valve. The selection of smaller and lighter butterfly valves has proven popular in the many marine applications.
Water itself can be hard on piping systems because it can cause oxidation, which means even marine valve materials for fresh water applications must be chosen carefully. More and more, stainless-steel valves and piping systems are installed in fresh water marine applications, replacing the previously common carbon steel materials.
Salt water is a different case altogether: a carbon-steel piping system would not last any length of time in this environment. Seawater valves are quite often bronze alloys, Cu/Ni or higher alloys such as Ni/Cr or titanium. Aluminum bronze is still popular because of its adequate seawater corrosion resistance combined with relatively low cost. Pressure classes for most marine applications are modest and usually less than 300 psi.
CRAFT BREWING & DISTILLING
Visiting a restaurant or bar that features a craft brewing operation reveals many shiny pipes, valves and tanks. These facilities are basically small process plants designed to distill and create alcoholic beverages. Valves and piping for this purpose are similar to biopharmaceutical valves in that they must be clean, with interior surfaces that will not attract or capture any organic material. This means ultra-smooth inside bores as well as cavity-free designs. These valves operate at low pressure and are almost always stainless steel or in some cases copper or bronze.
Another unique aspect of valves in this service are the end connections. These connections are categorized as hygienic fittings and have polished interiors as well as a mechanical end-clamp connection. Because of the difficulty of cleaning quarter-turn valves, those valves are less popular than slide-type gate valve, which have virtually no pockets or areas to entrain unwanted debris or organic material.
The biggest users of valves in solar energy are the solar-thermal units, which concentrate the heat of the sun and use that energy to heat transfer media to create steam. In other words, the transfer fluid is heated and circulated in a receiver to produce the steam. Valving for these facilities falls into two segments: piping for the heat transfer fluid and the steam-handling piping system.
Valves in the heat transfer system must handle the pressure and temperature generated in the heating process. Additionally, these valves need to be compatible with the heat transfer fluid itself. Valves and piping on the steam side follow the same design requirements as any other steam/turbine power plant.
Solar power plants that use the photovoltaic process for generating electricity do no not have the fluid piping requirements of solar/thermal plants and thus have no significant pipe and valve requirements.
IRON & STEEL
Iron and steel manufacturing and the piping/valve requirements for these two metals can be split into two distinct parts. Ironmaking is a strong user of many valves, both unique types and sometimes large in size. Iron is made in a blast furnace where iron ore, coke and other additives are cooked at about 2800°F (about 1538°C) degrees until molten iron is created.
The blast furnace uses large diameter, low-pressure hot-gas lines that run from the gas stoves through the blowing engine and into the blast furnace hearth. These pipe lines contain a variety of valves. The most popular hot-gas valve is the goggle valve, which is a combination knife gate that slides in and out of the pipeline bore. Other large outside diameter gate and check valves are used in the hot-gas system as well.
The blast furnace also requires a variety of water and steam lines. These lines and their accompanying valves are usually built to standard designs.
The pneumatic steelmaking process, also called the basic oxygen process, uses a mixture of scrap, molten iron, pure oxygen and additives to cook the steel. The most critical part of the process in regard to valves and piping are the valves used in oxygen service. These valves must be specially cleaned to remove all traces of grease and oil before they can be used in the pure oxygen line.
Most steelmaking in the United States today uses either the electric arc furnace or the continuous casting process. Neither require as much piping and valves as other processes.
The geothermal industry by nature deals with hot gas or steam located in the ground. Harnessing the energy of these geothermal sources is done at a variety of locations across the country. Depending upon the nature and temperature of the geothermal energy, the valve requirements can be similar to those for steam service, or they may only need be as robust as required for hot water systems.
Valves for aerospace applications are typically very small. The most common types are solenoid valves and small hydraulic valves used to manipulate the control surfaces such as the ailerons, flaps and rudder. Guided missiles and rockets use the same types of small and micro-sized valves.
The launching pads for orbital and space exploration rockets is very complex and contains a variety of pipe lines. There are lines for liquid fuel, which usually contain cryogenic valves. Other utility lines contain a variety of fluids at differing pressures and temperatures.
DAMS & HYDRO-ELECTRIC POWER
Large dams, especially those providing hydroelectric power, are full of valves of all sizes and types. There are gates, globes, checks, balls and butterflies, along with some very special valve designs used only in the water reclamation industry.
Dams normally are not created just to hold back water and create attractive recreational lakes. They usually are built to provide water resources and, in more and more cases, to provide renewable electrical energy.
The purpose of the valves in these structures is to adjust the output of the reservoir while maintaining the proper reservoir depth, both in times of flood or drought. Looking at the top of a moderate-size dam would reveal a number of rolling gates or sluices that provide the modulation of flow necessary to balance water supply and demand.
All dams of substantial size need to have a way of releasing water in controlled amounts because of changing reservoir capacity, downstream water demands or minimum stream flow requirements. These situations call for special valves designed to dissipate the large amount of energy created by the high head of water in the dam.
At first glance it might seem that virtually any type of shutoff valve might work. A closer look, however, at the operating conditions tells a different story. These outlet valves, which are releasing water, are doing so at huge volumes, at relatively high head pressures and at a resulting high velocity. The combination of output flow conditions can result in severe damage from cavitation at the valve outlet, so specially designed needle-type valves are often used for this demanding service.