On the Sea and Under the Ground
Today’s ships are much more than floating tanks.
MARINE VALVE INDUSTRY IS WIDE IN SCOPE AND VALVE NEED
By Greg Johnson
Most valve industry professionals who don’t live near the water, have little idea of the breadth of the marine valve industry. In the U.S., this industry is vibrant and interesting and equals many other valve industry segments in scope. It is stocked with virtually every type of valve, manufactured out of a host of common and not-so-common materials. An unpowered barge may contain a few valves for regulating ballast, while a modern supertanker will contain hundreds of valves of all sizes and types.
HISTORY OF MARINE VALVES
The birth of the steamship during the industrial revolution kicked off the marine valve industry. The steam and fire-belching engines that turned paddlewheels and propellers throughout the 1800s were all controlled by globe valves made of iron and brass. During the latter half of the 19th century, these early steam valve designs were adapted to other marine uses as the industry grew rapidly.
The development of the U.S. Navy “ironclads” (armored battleships) at the turn-of-the century set the pace for naval valve production that would reach a towering peak during World War II. Beginning in the mid-1950s, the Naval valve industry would further refine and define itself by providing the unique valves required for Admiral Hyman Rickover’s fledgling nuclear Navy.
The continuing use of steam to power merchant ships of all sizes helped maintain a huge market for lower pressure steam service valves until the move to diesel power was complete in the 1970s. The birth of the oil tanker in the early 20th century would also create opportunities for valve suppliers, and these opportunities are still viable in this age of the giant super-tanker.
THE MANY DUTIES OF MARINE VALVES
Marine valves perform a number of different duties both above and below decks. For example, all vessels need some form of energy to power their engines, and valves regulate the loading and storage of this commodity. There may only be one fuel valve on a diesel tugboat, but large cargo ships 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 on a large ship to aid in the ballasting of the vessel.
Water ballast and bilge systems are extremely important as well. These systems may use piping and valves that are hand-held size or as large as NPS 30 (national pipe size for a 30-inch valve). Needless to say, valves handling seawater must be hearty and designed to withstand the rigors of a harsh seawater environment. Firefighting piping systems are also important on ships since there are no local fire departments to call in case of an emergency at sea. Firefighting system valves must work when called upon, so their valves have to be ultra-reliable.
Fifty years ago, both gray water and black water (sewage) wastewater was just piped overboard while at sea. Today, that practice is taboo, so efficient wastewater piping systems are required to handle and process this unpleasant effluent. These systems also need to be very dependable and able to withstand the harsh wastewater environment.
Ships carrying liquid cargo obviously have need for extensive piping systems. These vessels, from oil barges to LNG tankers, are loaded with valves of every description. The valves need to be carefully selected to handle the products that run through them, such as petrochemicals or cryogenic LNG. But they also must have a stout exterior to hold up against the corrosive sea water environment.
For nearly a hundred years, the most common valves on ships and barges were gate, globe and check valves. Extra space is always at a premium on a ship. In the case of gate valves, the outside screw and yoke, rising stem design, often took up too much valuable space onboard. This resulted in the adoption of the non-rising stem (NRS) design, which became commonplace because of the additional headroom it afforded above the handwheel. The venerable NRS gate valve is still used primarily in marine applications.
Today’s ships and barges are home to virtually every type of modern valve, not just the old school gate, globe and check valves. Ball valves are increasingly popular, including metal-seated types. Still, the lined butterfly valve has probably made more inroads then any type in this segment, which was previously dominated by gate valves. The selection of the smaller and lighter butterfly valves also has proven to be a popular one for many marine applications.
Many tankers and tank barges are required to haul different fluids in multiple onboard tanks. The loading and diverting valves feeding these tanks are usually required to have block and bleed capability to keep from cross contaminating their liquid cargoes.
Automation has become very common on modern ships, and this translates to the piping systems. Automated valve packages are seen more and more in the engineering rooms of modern vessels. These systems often interface with sophisticated computer systems that are used to control all of the common shipboard engineering functions.
Because of oxidation, water is hard on piping systems. Even marine valve materials for fresh water applications must be chosen carefully. More and more, stainless-steel valves and piping systems are being installed in fresh water marine applications, replacing the previously common carbon steel materials.
Salt water is a different case altogether. Bronze valves or iron valves with bronze trim were the most common seawater service marine valves for a long time, and a carbon steel piping system will not last for any length of time in a salt-water environment.
Seawater valves today are quite often still bronze alloys, Cu/Ni or even higher alloys such as Ni/Cr or titanium. Aluminum bronze is still quite popular because of its adequate seawater corrosion resistance combined with relatively low cost. The most interesting material choice today, however, is titanium. Titanium is a noble alloy with extremely good corrosion resistance, especially in seawater service. But titanium has other advantages for the marine environment including its high strength and more importantly, light weight.
Although titanium piping systems (and valves) are expensive, the Navy has chosen the material for many of its key piping systems because of its overall lower cost of ownership. The titanium valves are particularly long-lived and require much less repair than other valves. Some metallurgists predict that titanium piping systems will even outlast the ships in which they are installed. Although complete titanium piping systems are relatively easy to fabricate and install, it is a tricky process to attach a titanium valve to non-titanium piping components because of the possibility of galvanic corrosion. Insulating bolt sleeves and gaskets must be used to keep this type of corrosion from occurring.
MARINE VALVE STANDARDS AND SPECIFICATIONS
In addition to some American Society of Mechanical Engineers (ASME) standards, piping systems for marine use are governed by documents written by the American Bureau of Shipping and the United States Coast Guard.
Valves for use by the Navy must meet even stricter standards. Most of these valves are Navy-owned designs that are built per quotation for each specific ship-building project. Prospective bidders must meet the Navy’s stringent quality requirements before they are allowed to bid on a valve package.
Providing nuclear service valves for the Navy requires additional quality requirements and documentation. Still tighter are the requirements for components in the Navy’s “SUBSAFE Program.” This program is designed for “critical systems whose failure or lack of operation will have catastrophic consequences.” The program was developed after investigations into the loss of the USS Thresher, a nuclear submarine that went down with all hands aboard in 1963. The program, which is very successful and actively used today, is applicable to all critical valves that are used in U.S. nuclear submarines.
MARINE VALVE APPLICATIONS
From stem to stern, tankers of all sizes are covered with valves. This valving includes a variety of block valves, with many rising and rotating stem, double block and bleed types. A special type of tanker, the LNG ship, requires unique product piping and valving systems.
LNG tankers contain large insulated tanks similar to giant thermos bottles but designed to carry cryogenic liquid natural gas at -256° F and pressures from 100 to 250 psi. The product valving on these ships has to be designed for cryogenic temperatures, and on-off and regulating valves must have extended bonnets so the packing area does not freeze, rendering the valve inoperable.
Chemical and oil barges are built to carry both pressurized and non-pressurized loads. In addition to the usual product regulation and control valves, pressurized barges must have adequately sized relief valves to keep the tanks from over pressuring as they heat up.
The Navy shipbuilding program consumes thousands of valves yearly, with needs depending upon which types of ships are built. These projects could require nuclear-grade pressure seal valves, titanium butterfly valves, Ni/Cr ball valves or even mundane bronze gate and globe valves.
While it is true that the U.S. shipbuilding industry is not what it was 50 or even 25 years ago, there is still work for the nation’s shipbuilders and applications where many marine valves are needed. Shipyards on all three coasts are active today in constructing barges, work craft, smaller commercial ships, oil industry vessels, and of course, all U.S. Navy ships. In addition to new ship construction, there is still a viable refurbishment and repair industry that also consumes a large quantity of marine valves each year.
Although it seems to operate under the radar, the marine valve industry overall is strong and offers many opportunities for valve manufacturers and distributors alike.
Greg Johnson is a contributing editor to Valve Magazine and president of United Valve (www.unitedvalve.com), Houston, TX. Reach him at email@example.com.
MINING: HIGH SOLIDS REQUIRE REPLACEABLE OR HIGH PERFORMANCE VALVES
By Craig Bekins
Today, when we discuss the mining industry, it’s hard not to picture a massive explosion ripping apart the side of a mountain, the remnants of which are then removed using the largest loaders and trucks imaginable. For the valve industry, however, the interesting processes happen after the ore has been separated.
To gain a “valve” perspective, we must first focus on the differences between mining materials for construction and mining for industrial uses. The majority of mines produce aggregates for the construction segment. As such, most of them have little or no application for industrial valves. A smaller number of mines are used to get materials for facilities that produce industrial products, so they seek coal, iron ore, copper, nickel, gold and other resources.
The common denominator in the processing of such industrial minerals is a moderate to high level of solids. This requires either a low-cost design that can be replaced regularly or a very robust design that can withstand the rigors of solids-laden applications for an extended period of time.
VALVE TYPES USED IN MINING
Valves with soft replaceable sealing elements are relatively inexpensive to produce and repair and are commonly used in processes where the operating temperature is less than 375º F (190º C) and where the pressure is relatively low (Class 300 max). Examples used in mineral processing are rubber-lined knife gate valves and butterfly valves as well as sleeved plug valves. In these designs, a soft sacrificial material provides tight shut-off, but the resilient material is quickly worn by the erosive slurry passing through the valve, and it is not uncommon for valves of this type to be repaired or replaced on a weekly basis.
These valve types are also limited in that they cannot be used at high temperatures or at high pressure. Therefore, the use of severe service ball valves has increased significantly over the past 15 to 20 years. Severe service ball valves, as the name implies, are used when increased temperature and/or pressure combine with erosive and possibly corrosive media to exceed the capabilities of other valve types. It is in these situations where we find some of the most interesting and challenging valve applications.
The first such application is transport of ore from the extraction site, which can be located high in the mountains, to either a shipping port or to a processing plant. The application involves mixing the ore with water to create a slurry that is carried through a high-pressure pipeline to its destination. These slurry pipelines can range in size from six to 24 inches in diameter and in some cases can be over 100 kilometers long. In this application, valves are most commonly used to isolate the pumps that are tasked with keeping the slurry moving. In doing so, the valves are exposed to high pressure and a significant amount of solids. This requires specific features such as super-hard coatings on the interior surfaces of the valve to resist the erosive forces of the high flow or high differential pressure slurry and heavy- duty drive trains to ensure that the valve does not seize despite the high level of solids inherent in this application.
Slurry pipelines operate at ambient temperatures and have little to no corrosive media. Therefore, valves for this application can be made from carbon steel and other relatively standard materials. Valves in the slurry pipeline segment are typically automated with self-contained electro-hydraulic actuators, which are ideal for this application’s large output torque and likely installation in remote locations.
WHAT’S BEING MINED
Once the ore is separated from the earth’s crust and transported from the extraction pit, what happens next depends on what mineral is being processed. In the case of precious and semi-precious metals (gold, nickel, etc.), the desired mineral must be separated from other elements and impurities that make up the rock. In many cases, this can be accomplished by traditional methods such as smelting (pyrometallurgy); however, older smelting processes are expensive (energy intensive) and are harmful to the environment.
These realities—and in the case of nickel, a shortage of suitable ore beds—have given rise to the use of hydrometallurgy and more specifically, pressure leaching to extract and refine these minerals. Although the process was developed in the mid 20th century, it was not used on a large scale until the late 1980s. Since then, several multi-billion dollar facilities have been built to use this efficient and environmentally responsible process, which is more akin to a chemical plant than a mine. It is in the pressure-leaching circuit that we find one of the most demanding valve applications in mining. Here, severe service valves isolate not only pumps but more importantly, the autoclaves where the prepared and heated slurry begins the pressure-induced chemical reaction that turns rock into gold or nickel.
Pressure leaching is similar to the slurry transport application discussed earlier, but because of the high temperature and presence of corrosive elements, standard materials are not appropriate. In fact, at the front end of the autoclave, it is common to find various grades of duplex stainless-steel. Once the “clave” itself is reached, we find titanium or Hastelloy and nothing else. These are far from standard materials and require the valve designer to pay close attention to all aspects of the design to ensure that the valve remains operational. It only takes one overlooked bushing in the wrong material to seize the valve and potentially shut down a multi-billion dollar plant. For this reason, there are only a handful of valve companies entrusted to this duty.
In this article, we have highlighted but a few of the many valve applications that fall under the category of mining—many more exist, including valves used in steel production and coal conversion. In all cases, valves used in mining must be purpose-built and designed with the rigors of the application firmly in mind.
Given that valves are playing an increased role in both the transport and processing of industrial minerals, the outlook for the valve industry in this area is relatively positive. However, this optimism must be tempered by the inherent volatility of the mining market as a whole, which will continue at a slower pace as the global economic recovery takes hold. Still, mining is poised to take advantage of the next boom cycle…and, of course valves will be there doing their part.
Craig Bekins is product manager–severe service ball valves, valve specialist in HPAL process with experience on major projects such as MurrinMurrin, Coral Bay Nickel, Goro and more for Velan Valve Corporation (www.velan.com). Contact him at firstname.lastname@example.org.
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