Common Metals & Materials Used in Butterfly Valve Manufacture

Many different materials can be used in the design of a butterfly valve. A typical butterfly valve will use several different materials within its construction to achieve the best combination of functionality and cost. The following briefly describes the most common materials that may be used in the design of an effective butterfly valve, highlighting their relative advantages and disadvantages. 

Advantages of materials used for Butterfly Valves

Carbon Steel

Carbon steel is an alloy of iron where the main alloying element is carbon. Generally, no other alloying elements are added to control the properties of the material. For butterfly valve construction, carbon steel is most often used to form the body and disc of the valve using the sand casting process.

Carbon steels are available in several different grades. The most common grades used for valve bodies and discs are cast grades ASTM A216 WCB (Weldable Cast B-grade) and LCC (Low Carbon Content) steels. WCB material is most suitable for high temperature use, whereas LCC can be used at low (sub-zero) temperatures.

Main Advantage of carbon steel:

The cost - carbon steels are relatively cheap, and valves produced from carbon steels provide a cost-effective solution in environments where other factors are considered less important than cost.

Main disadvantage of carbon steel:

Poor corrosion resistance. This can be overcome by surface protection such as paint, provided that the line media does not corrode the valve from the inside.

Stainless Steel

The definition of a stainless steel is an alloy of iron with a minimum chromium content of 10.5%. The effect of the chromium is to form a self-healing layer of chromium oxide on the surface of the material. When the surface is broken by mechanical damage such as scratching, the chromium quickly reacts with oxygen in the air, so preventing the oxygen from reacting with the iron and forming iron oxide (rust). An ever-increasing number of stainless steels are available, of which the simple iron-chromium-nickel grades are most often termed 'stainless steel'.

Stainless steels can be further classified as ferritic, austenitic, martensitic, duplex and precipitation hardenable. This classification is based on the microstructure that is developed in the material by varying the alloying elements present. For valve construction, the most common grades used are austenitic and duplex. These are described briefly below.

Austenitic stainless steels

Austenitic stainless steels, in addition to chromium, contain elements such as nickel, which have the effect of retaining the high temperature face-centred-cubic austenitic structure at temperatures where it would normally have transformed to the ferritic body-centred-cubic structure. This face-centred cubic structure gives the material improved toughness and ductility compared to the ferritic grades. Depending on the nickel content, the tough austenitic structure can be retained even at extremely low temperatures, allowing the material to be used in cryogenic applications. Improved resistance to pitting corrosion can be achieved by adding molybdenum to the alloy.

Duplex stainless steels

Duplex stainless steels contain a balanced structure of both the austenitic face-centred cubic and ferritic body-centred structure of iron. This structure is developed by carefully controlling both the alloying elements and the heat treatment performed on the alloy to obtain a structure consisting of 50% austenite and 50% ferrite. The result is an alloy that combines the higher strength of ferrite with the improved toughness of austenite. The super duplex grades contain higher levels of chromium and molybdenum to enhance their resistance to pitting and crevice corrosion.

Nickel Alloys

Nickel alloys are used in valve components where severe service conditions are encountered. These alloys are particularly useful in harsh corrosive environments, which would attack stainless steels by breaking down their protective oxide layer.

Hastelloy nickel-based alloys are most often used in valve construction. There are several different forms of Hastelloy, with each being tailored by adding specific alloying elements is varying proportions to suit particular service conditions.

The main disadvantage of nickel alloys is their weight and cost. Nickel alloys have a high density and their cost can be many times that of basic stainless steels.

Titanium Alloys

Titanium alloys combine high strength with light weight and excellent corrosion resistance, having the highest strength-to-weight ratio of any metal. In a similar manner to stainless steels, titanium alloys gain their corrosion resistance by the development of a protective oxide layer on its surface. They are particularly resistant to corrosion by seawater, in particular in systems where hypochlorite is present to prevent biofouling.

The main disadvantage of titanium alloys is their cost, being around ten times as expensive as basic stainless steels or nickel aluminium bronze. The material is also difficult to process due to its highly reactive nature. Special casting techniques are required to prevent reaction with oxygen during melting and pouring.

Nickel Aluminium Bronze

Nickel aluminium bronze is a copper-based alloy containing approximately 10% aluminium, 5% nickel and 5% iron. The nickel aluminium bronze alloys provide excellent corrosion resistance, particularly in seawater environments. They also strongly resist the formation of a bio-film, which can cause increased corrosion problems in stainless steels.

Nickel aluminium bronze has a cost approximately equivalent to that of basic grades of stainless steel. One disadvantage of this material is that it is more anodic than most materials, so that if a nickel aluminium bronze valve is coupled to a stainless steel pipe, then corrosion of the valve in seawater could be fairly rapid.

The above shows that many different materials can be used in valve construction. The ultimate choice depends on several factors including service conditions, cost and required life expectancy. Choice can also be strongly influenced by the material of construction of the pipeline, where galvanic corrosion issues must also be taken into account.

Maharashtra Govt. approves 1600 cr desalination project

 Maharashtra Chief Minister Uddhav Thackeray has approved to set up a desalination project with a capacity of 200 MLD in Mumbai.The project will entail an investment of Rs 1,600 crore. The project will be set up over 30 acre at Manori, Malad, and is expected to be completed in four years. After tapping about six possible locations, the Brihanmumbai Municipal Corporation (BMC) has finalised Manori for setting up the project.The capacity of the plant can be raised to 400 MLD in the future, which can make up for the shortfall of 10 percent of the total water consumption of the city of 3,800 MLD when there is poor rainfall.

The detailed project report will be prepared in around nine months and take another three months to complete the tendering process.The actual completion of the project will need around three more years. The site has been finalised by the technical team as it has no mangroves around it, good quality of water and connected by roads, among other reasonsBMC had tapped five other locations, including Versova, Gorai, Malad, among others for the project. The project will help to make up the shortfall of potable water in summer due to the late arrival of monsoon or shortfall in expected water stock. The operational cost of the project will reduce significantly if operated on solar power.The operational cost of the desalination plant is higher than the dam-based water-supply projects and has been one of 

the reasons behind the delay to the project, which has been planned for years. BMC expects it to be 50% more than its existing system of dam-based water supply.

Desalination is a process that takes away mineral components from saline water. More generally, desalination refers to the removal of salts and minerals from a target substance,as in soil desalination, which is an issue for agriculture.

Saltwater (especially sea water) is desalinated to produce water suitable for human consumption or irrigation. The by-product of the desalination process is brine. Desalination is used on many seagoing ships and submarines. Most of the modern interest in desalination is focused on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few rainfall-independent water sources.

There are approximately 16,000 operational desalination plants, located across 177 countries, which generate an estimated 95 million m3/day of freshwater.Currently, desalination accounts for about one percent of the world’s drinking water.Desalination is particularly prevalent in countries located in the Middle East and North Africa region, such as Saudi Arabia, the UAE, and Kuwait.Desalination is also an important source of water in the Small Island Developing States.

Due to its energy consumption, desalinating sea water is generally more costly than fresh water from surface water or groundwater, water recycling and water conservation. However, these alternatives are not always available and depletion of reserves is a critical problem worldwide. Desalination processes are usually driven by either thermal (in the case of distillation) or electrical (in the case of reverse osmosis) as the primary energy types.

Currently, approximately 1% of the world's population is dependent on desalinated water to meet daily needs, but the UN expects that 14% of the world's population will encounter water scarcity by 2025.Desalination is particularly relevant in dry countries such as Australia, which traditionally have relied on collecting rainfall behind dams for water.

Kuwait produces a higher proportion of its water through desalination than any other country, totaling 100% of its water use.

PCTFE vs PTFE - A Comparison of Two Very Similar Polymers

 The difference between PTFE and PCTFE is mainly in the chemical structure. The addition of one Chlorine atom in place of one Fluorine atom leads to a massive change in its properties and application.

PTFE is a versatile and cost effective material of average tensile strength. It has very good thermal properties and excellent chemical inertness, especially to strong acids. The coefficient of friction is unusually low and believed to be lower than any other solids. PTFE is an outstanding electrical insulator over a wide range of temperatures and frequency.

At the molecular level, PTFE is a linear polymer with high molecular weight (Length of Polymer Chains) and Crystallinity level of 50-70% depending on the processing conditions.

Due to its high viscosity, PTFE cannot be processed using conventional polymer processing techniques. Hence, PTFE is processed by cold forming operation followed by heat treatment (sintering) during which polymer particles fuse to form a solid moulding.

PCTFE has a higher tensile strength than PTFE and good thermal characteristics. It is non-flammable and heat resistant up to 180°C. PCTFE is resistant to the attack of most chemicals and oxidizing agents, due to the presence of high fluorine content. However, it swells slightly in halogenated compounds, ethers, esters and aromatic solvents.

PCTFE has one of the highest limiting oxygen index. It has good chemical resistance and also exhibits properties like zero moisture absorption and non-wetting.

PCTFE has a low coefficient of thermal expansion and its dimensional stability makes it attractive for use as a component of a structural part where the high temperature and chemical resistance of fluoropolymers is required.

PCTFE is melt processable by conventional process techniques such as Injection moulding, Extrusion and Compression moulding. 

PCTFE is a homopolymer of chlorotrifluoroethylene (CTFE), whereas PTFE is a homopolymer of tetrafluoroethylene. PCTFE is a harder and stronger polymer, with better mechanical properties than PTFE. Though PCTFE has excellent chemical resistance, it is still less than that of PTFE. PCTFE has lower viscosity, higher tensile strength and creep resistance than PTFE.

Even though PTFE remains a niche polymer among more generic materials such as PP (Polypropylene), PVC, PE (Polyethylenes, such as HDPE and LDPE), and even Nylons, within the engineering space it is now quite common. Most applications involving high temperature, corrosive chemicals, high voltages, or high wear/friction now look to PTFE automatically as a solution. 

Despite this, there do exist applications where PTFE does not fit the bill and a compromise must be made. For example, applications where high dimensional stability is needed across a wide temperature range, PTFE tends to fall short. The high linear thermal expansion coefficient of PTFE means that it cannot hold its dimensions as temperatures vary. In such a situation, we have seen PEEK being adopted. While PEEK does do the trick, it is also 10X the cost of PTFE.

Similarly, certain applications where cost is a constraint need to make do with POM (Delrin), or even PVC, where PTFE cannot be used. In such a scenario, we possibly forego some of PTFE’s key properties.

Over the years a variety of new polymers that have been developed to fill the performance and commercial gaps between PEEK and PTFE. These include PFA, FEP, PEK, PPS (Ryton), and PCTFE.

Although not well known, PCTFE forms an ideal substitute for PTFE in certain applications where PTFE is unable to perform adequately. The table below is meant to offer a snapshot comparison of the two, such that any application engineer can evaluate the key differences.

As you can see from the above chart, PCTFE and PTFE each have unique advantages and disadvantages when compared with one another. Like all polymers, the application needs to be properly understood and the commercials need to be weighed in before any decision can be made.

However, it is fair to say that when dimensional stability across a temperature range is a must, PCTFE is growing to become the most effective substitute for PTFE.

Quazless participated in the 10th China International Fluid Machinery Exhibition with HANDA and DESW

 Quazless participated in the 10th China International Fluid Machinery Exhibition with HANDA and DESW

On December 9, 2020, the 10th China (Shanghai) International Fluid Machinery Exhibition (IFME2020) hosted by China General Machinery Industry Association was grandly opened at the National Convention and Exhibition Center (Shanghai).

"China (Shanghai) International Fluid Machinery Exhibition (IFME)" is the only fluid machinery industry in China hosted by China General Machinery Industry Association with a large scale, high industry authority, rich exhibits, advanced exhibits, and visitors. Highly large-scale professional exhibition.

The exhibition is mainly divided into several major areas such as valves, pumps, fans, compressors, pipe fittings, vacuum equipment, reduction gears, air separation, etc., which concentratedly showcased the latest achievements in technological innovation and product development of domestic and foreign fluid machinery manufacturing industries. .

At the opening ceremony, Mr. Wang Ruixiang, President of China Machinery Industry Federation, attended the opening ceremony as a special guest, and Ms. Huang Li, President of China General Machinery Industry Association, delivered an opening speech.

Oriole: This exhibition was postponed from June this year to today after a lot of efforts, consultation and communication after our country has achieved a major victory in the fight against the new crown epidemic. It is not easy! Therefore, this exhibition is also a collective appearance for the general machinery industry in fighting the epidemic, resuming production, and maintaining steady growth of the industry!

After the epidemic, the first major military parade for the entire industry chain of the fluid machinery industry, 500+ industry leaders arrived as scheduled, bringing their blockbuster products to the National Convention and Exhibition Center (Shanghai) 1.1H, 2.1H Hall more than 50,000 square meters of exhibition area, highlighting The hard core strength of China's fluid machinery has shown the vigorous vitality and development potential of China's fluid machinery industry and market to the industry. The next month’s promotion and the online Zhongvalve BTB network promotion platform have received close attention from the personnel with professional brand planning ability and considerate service.

During the exhibition, the organizer not only invited important users in the industry, engineering companies, foreign embassies in China, domestic and foreign industry organizations to visit, but also held technology summit forums with rich content and various forms, international industry forums, technology exchange meetings, and new Activities such as product launches and user signing ceremonies. In order to fully display the industry influence of the exhibition, more than 100 professional media in the industry conducted all-round publicity and reports on participating and exhibiting companies from different angles and multiple channels during the exhibition.

The organizer of IFME2020, Zhongtong Xiete, carefully planned two "Procurement Matchmaking Meetings"

The most impressive thing is this college exhibition area

Shanghai Jiaotong University, Shanghai Institute of Technology and other universities have demonstrated some research results, which are conducive to the integration of industry and enterprises

QUALZESS brings its brand HANDA and DESW booth at 1.1H Valve Hall J09.

Visitors from all over the country and various industries have shown strong interest in Gotshanda products and have received formal inquiries.

Thanks again to the friends who came to the exhibition booth.

Butterfly valves take control

Mark Nymeyer discusses the advantages and limitations of butterfly valves, and highlights developments that are making them more suitable for flow control.

Butterfly valves are lighter, smaller and weigh less than other kinds of control valves, making them the best choice for regulating flow in many applications. Standard butterfly valves have, traditionally, been used for automated on/off applications, a role for which they are well suited. However, when it comes to regulating flow in a closed-loop system, some engineers consider them unacceptable.

Butterfly valves use a rotating disk to control flow through a pipe. The disk is generally operable through 90 degrees, so they are sometimes called quarter-turn valves. Typically, they are used when economy is a consideration. When tight shutoff is needed, butterfly valves with soft elastomer seals and/or coated disks can be used to deliver the required performance. High performance butterfly valves (HPBVs) - or double offset valves - are now the industry standard for butterfly control valves and are widely used for throttling control. They do a good job for applications that have a relatively constant pressure drop or for slow process loops.

Advantages of HPBVs include a straight through flow path, high capacity, and the ability to easily pass solids and viscous media. They generally have the lowest installed cost of any valve type, especially in NPS 12 and larger sizes. Their cost advantages compared to other types of valves, increase dramatically in sizes over 12in.

They can offer good shutoff performance over a wide range of temperatures, and are available in different body designs including wafer, lugged and double flanged. They weigh much less than other types of valves and are more compact. For example, a 12in ANSI class 150, double flanged segmented ball valve weighs 350lb and has a 13.31in face to face dimension, while a 12in lugged butterfly valve equivalent weighs only 200lb and has a 3in face to face.

Limitations

Butterfly valves do have limitations that make them unsuitable for flow control in some applications. These include a limited pressure drop capability compared to globe ball valves with greater potential for cavitation or flashing.

Because the large surface area of the disk acts like a lever, applying the dynamic forces of flowing media to the drive shaft, standard butterfly valves are generally not used in high pressure applications. When they are, actuator sizing and selection becomes crucial.

Oversizing of butterfly control valves sometimes occurs and will negatively impact process performance. This can result from using line-size valves, especially with high-capacity butterfly valves. It can increase process variability in two ways. Firstly, oversizing puts too much gain in the valve, leaving less flexibility when adjusting the controller. Secondly, an oversized valve is likely to operate more frequently at lower valve openings, where seal friction can be greater in butterfly valves. Because an oversized valve produces a disproportionately large flow change for a given increment of valve travel this phenomenon can greatly exaggerate the process variability associated with deadband due to friction.

Specifiers sometimes use butterfly valves for economy or to fit a given line size, without considering their limitations. There is a tendency to oversize butterfly valves to avoid swaging down piping, which contributes to poor process control.

The largest limitation is that the ideal throttling control range is not as wide as a globe or segmented ball valve. Butterfly valves generally do not perform well outside a control range from about 30 to 50% open.

Optimal control performance

In general, when a control loop behaves in a linear manner and the process gain is close to unity, a loop is easiest to control. Therefore, a process gain of 1.0 becomes the objective for good loop control, with an acceptable range of 0.5 to 2.0 (a range of 4:1).

Best performance results when most loop gain comes from the controller. Notice in the gain curve of Figure 1, the process gain gets quite high in the region below about 25% valve travel.

Process gain defines the relationship between changes in process output and input. The travel over which process gain stays between 0.5 to 2.0 is a valve’s optimal control range. When process gain is not within 0.5 to 2.0, poor dynamic performance and loop instability can occur.

Butterfly valve disk design has a significant effect on valve flow rate as the valve travels from closed to open. A disk with an inherent equal percentage characteristic can better compensate for changing pressure drops as the flow changes. Equal percentage trim will give a linear installed characteristic for changing pressure drops, which is ideal. The result is a more accurate, one-to-one change between flow rate and valve travel.

Figure 1: Comparison of globe valve and butterfly valve. The best control occurs when gain is 0.5 to 2.0. Globe valves control well across a broad travel range, but standard butterfly valves are limited to 30-50% travel.

Butterfly valves recently became available with disks having an inherent equal percentage flow characteristic. This delivers an installed characteristic that results in an installed process gain within the desired 0.5 to 2.0 range over a wider travel. This results in significantly improved throttling control, especially in the lower travel ranges.

This design provides good control with acceptable gain of 0.5 to 2.0 from about 11% open to 70%, a control range improvement of nearly threefold when compared to a typical high-performance butterfly valve (HPBV) of the same size. The equal percentage disk thus delivers overall lower process variability.

Butterfly valves with an inherent equal percentage characteristic, such as the Control-Disk Valve, are ideal for processes that require precise, throttling control performance. They can control closer to the target set point regardless of process disturbances, which results in a reduction in process variability.

Improving control

If a butterfly valve is operating poorly, simply replacing it with a properly sized valve may solve the problem. For example, a paper company was using two oversized butterfly valves to control water removal from pulp stock. The two valves were operating below 20% travel, causing process variability of 3.5 and 8.0%, respectively. They spent most of their service life in manual mode.

Two properly-sized NPS 4 Fisher Control-Disk butterfly valves with digital valve controllers were installed. The loops now operate in automatic mode, and process variability went from 3.5% to 1.6% for the first valve, and 8% to 3.0% for the second valve, without any special loop tuning required.

Poor water pressure and flow control from the coolant system in a steel mill caused end product inconsistency. Nine installed HPBVs could not effectively control the flow of water as required.

The mill wanted to install valves that would better control the process, and needed to minimise installed cost. The mill would have spent $10,000 for piping changes per valve to switch from the HPBVs to segmented ball valves. Instead, Emerson suggested its Control-Disk butterfly valves fitting the current HPBV face-to-face dimensions.

One Control-Disk valve was tested side-by-side with one of the nine existing HPBVs, and it performed to specified requirements. The mill replaced the remaining eight HPBVs within the year, each with a Control-Disk valve and this eliminates the need for $90,000 in piping changes for segmented ball valves, and the roughly 25% increased cost of ball valves versus butterfly valves.

The Control-Disk valves provide precise control and help eliminate end-product variability. The steel mill estimated the nine installed Control-Disk valves result in annual savings of about $1 million.  

Conclusions

HPBVs with digital positioners have a lower initial installed cost than most other valve types, and can provide an adequate control range when sized properly. They have high capacity and minimal flow restriction. Butterfly valves with inherent equal percentage trim offer an opportunity for an expanded control range, similar to that of a globe or ball valve and only take up the space of a HPBV.

When selecting valves, especially HPBVs, make sure they are sized correctly, or they could wind up being controlled manually from the control room. It is also important to consider the valve style, inherent characteristic and valve size that will provide the broadest control range for the application.

Mark Nymeyer is a global marketing communications manager at Emerson Automation Solutions for flow controls.

http://handavalve.com/en/article-11441-35247.html

HANDA exhibit at VALVE WORLD ASIA 2017

One of the largest valve exhibitions held globally in Suzhou, were recently attended by HANDA for the second time with very promising customer inquiries.

VALVE WORLD ASIA hosts approximately MANY visitors from over 30 countries on a bi-annual basis to demonstrate a complete range of valve & fluid controls as well as the latest technology developments in this much specialized industry sector.

The HANDA display was attended by many overseas visitors to discuss possible future supply of valve products manufactured by HANDA in Xiamen. This was the first major mainland China exhibit in which the company participated so a special effort was made to ensure that the display was up to international standard of presentation.

Visitors from countries such as  France, Spain,Iran, Denmark, Swiss,Korea, Russia,  Taiwan, Malaysia, Turkey all showed great interest in the HANDA products, with formal inquiries already received.

HANDA Display with Global Appeal

DESW is going to VALVE WORLD ASIA Sep 23 to Sep24, 2015, Suzhou

DESW Fluid Control, the company responsible for continually offering Valves Industry quality products, service for more than 30 years is pleased to invite you to the following business exhibition event.

“VALVE WORLD ASIA Sep 23 to Sep24, 2015, Suzhou

You are more than welcome to join us for a business coffee, a friendly chat & the opportunity to know each other better & learn more about what we have to offer to your business & Cater your needs.

Our full range valves products, including Lip-seal ball valves, Double offset butterfly valves, accessories, etc by using different required material will be exhibited during the show.

We look forward to seeing you at  148 stand, wishing you safe travel and every success in your business.

Thank you

The Management and Staff