What metal material can be used for valve seal?

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The valve seal is the key part to determine valve performance. The other factors like corrosion, friction, flash, erosion, oxidation, and ect should be considered when selecting sealing surface material. Valve seals are usually divided into two categories, one is a soft seal such as rubber (including butene rubber, fluoro rubber, etc.), plastic (PTFE, Nylon, etc.). The other is metal type hard seal, mainly including Copper alloy (for low pressure valves), Chromium stainless steel (for common and high pressure valves), Stellite alloy (for high temperature and high-pressure valves and strong corrosion valves), Nickel base alloy (for corrosive media). Today here we will mainly introduce the metal materials used in the sealing surface of the valve.

 

Copper alloy

Copper alloy offers better corrosion and abrasion resistance, suitable for the flow medium such as water or steam with PN≤1.6MPa, the temperature does not exceed 200℃. The sealed auxiliary structure is fixed on the valve body by surfacing and melting casting method. The commonly used materials are cast copper alloy ZCuAl10Fe3, ZCuZn38Mn2Pb2, etc.

 

Chromium stainless steel

Chrome stainless steel has good corrosion resistance and is usually used for water, steam and oil and the media of which temperature does not exceed 450℃. The sealing surface of Cr13 stainless steel is mainly used for gate valves, globe valves, check valves, safety valves, hard-sealed ball valves and hard-sealed butterfly valves made of WCB, WCC and A105 carbon steel.

 

Nickel base alloy

Nickel base alloys are important corrosion-resistant materials. Commonly used as sealing cover materials are: Monel alloy, Hastelloy B and C. Monel is the main material resistant to hydrofluoric acid corrosion, suitable for alkali, salt and acid solvent medium with a temperature of -240 ~ +482 ℃. Hastelloy B and C are corrosion-resistant materials in the sealing surface material of valve, suitable for corrosive mineral acid, sulfuric acid, phosphoric acid, wet HCI gas and strong oxidizing medium with a temperature of 371 ℃ (hardness of 14RC) and chlorine-free acid solution with a temperature of 538 ℃ (hardness of 23RC)

 

Carbide

Stellite alloy has good corrosion resistance, erosion resistance and abrasion resistance, suitable for different applications of the valve and temperature – 268 ~ + 650 ℃ in a variety of corrosive media, is a kind of ideal sealing surface material, mainly used in cryogenic valves (- 46 ℃ -254 ℃), high-temperature valve (valve working temperature 425 ℃ >, body material for WC6, WC9, ZGCr5Mo the wear resistance of the valve (including different working temperature level of wear resistance and erosion resistance of valve), sulfur resistance and high-pressure valve, etc. Due to the high price of Stellite alloy for surfacing. For the black water system and mortar system used in coal chemical gas production, the ball surface of the extremely hard wear-resistant ball valve is required to use the supersonic spray WC(Tungsten carbide) or Cr23C6(Chromium carbide).

 

We provide better sealing parts obtained from qualified hard metal material to the specific density required by valve applications. Call us today for your industrial valve demands!

 

Gate valves used for nuclear plant

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Nuclear valve refers to the valves used in the Nuclear Island (NI), Conventional Island (CI) and auxiliary facilities, the balance of Nuclear Island (BOP) system of the power plant. These valves can be divided into class Ⅰ, Ⅱ, Ⅲ, non-nuclear according to its security requirements in sequence. Valves are the most used control equipment transporting flow media and the essential part of the nuclear power plant.

Nuclear Island is the core of a nuclear power plant where nuclear energy is converted into thermal energy, including the Nuclear Steam Supply System (NSSS) and Nuclear Island auxiliary facility (BNI). The NCI is the workhorses of nuclear power plants, where heat is converted into electricity (including steam turbines all the way to power output). The usage of valves in the three systems of NI, CI and BOP is 43.5%, 45%, and 11.5% respectively.

A pressurized water reactor nuclear power plant will need about 1.13 million NI valves, which can be divided into gate valves, globe valves, check valves, ball valves, butterfly valves, diaphragm valves, pressure relief valves and regulating (control) valves according to the types of valves. This section mainly introduces gate valves in nuclear safety (specification) classes Ⅰ and Ⅱ.

The diameter of gate valves for Nuclear Island is generally DN 80mm-350mm. Forgings are suggested; be used for gate valve bodies of class grade Ⅰ and castings are allowed for gate valve bodies of Nuclear class 2 and 3. However, forgings are often used because the casting quality is not easy to control and be guaranteed. The valve body and bonnet of the nuclear valve is usually flange connected, which adds a lip sealing welding process and makes the sealing more reliable. In order to prevent the leakage of the medium, the double layer packing belt is usually adopted, and the Disc spring pretension device is used to prevent the packing loosening. These gate valves can be driven manually or electrically. The influence of the rotational inertia of the motor on the closing force should be taken for electric transmission device of the electric gate valve. It is better to use the motor with a braking function to prevent overload.

According to its body structure, nuclear gate valve can be divided into wedge elastic single gate valve, wedge double gate valve, parallel double gate valve with spring pretension and parallel double gate valve with top block.

Wedge type elastic single gate valve is characterized by its reliable sealing seats and the angle matching between the sealing surface of gate and valve body is required, which is widely used in the main loop system of nuclear power plants. Wedge-type double-plate gate valve is a common valve in thermal power station, its wedge double-plate angle can be adjusted by itself, more reliable sealing and convenient maintenance.

A load of parallel double gate valve with spring preloading will not increase sharply when the gate is closed, but the gate never releases the valve seat made by the spring when it is opened and closed, which leading more sealing surface weariness. The top block parallel type double gate valve provides a more reliable sealing performance which using the top block to make the inclined plane of the two gates stagger to close the gate valve.

Gate valve without packing is also used in the nuclear island. The hydraulically operated gate valve that depends on its own pressurized water to push the piston to open or close the valve. The fully enclosed electric gate valve uses a special motor to operate the gate by means of an inner planet decelerating mechanism which is immersed in water. However, these two gate valves have the disadvantages of complex structure and high cost.

 

Generally speaking, the features of gate valves for nuclear islands should be:

1) Welded hydraulic double gate plate parallel gate valve with a nominal pressure PN17.5 Mpa, working temperature up to 315℃ and nominal diameter DN350~400mm.

2）Electric wedge-type double gate valve applied in light water coolant primary circuit would be nominal pressure PN45.0Mpa, temperature 500℃ and nominal diameter DN500mm.

3）Electric wedge-type double gate valve used in the primary road of nuclear power plant with graphite-moderated reactor should be nominal pressure PN10.0Mpa, nominal diameter DN800mm and operating temperature up to 290℃.

4) Welded connected electric elastic plate gate valve is adopted on steam and process water pipes of steam turbine plant with a nominal pressure pn2.5mpa, working temperature 200℃, nominal diameter DN100~800mm.

5）The double gate valve with diversion hole is used in the high power graphite-moderated boiling water reactor nuclear power plant. Its nominal pressure is PN8.0MPa while the opening or closing of the valve carried when the pressure drop is ≤1.0MPa.

6) Elastic plate gate valve with frozen sealing packing is ideal for fast reactor nuclear power plant.

7) Internal pressure self-sealing bonnet wedge-type double gate valve for water-hydro power reactor unit with nominal pressure pn16.0mpa and nominal diameter DN500mm.

8) Wedge-type double gate valves with butterfly springs on travel parts are normally bolted flanged and sealed welded.

Which material is better for industrial valves body? A105 or WCB?

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The common material of valve body includes carbon steel, low-temperature carbon steel (ASTM A352 LCB/LCC), alloy steel (WC6, WC9), Austenitic stainless steel(ASTM A351 CF8), cast copper-alloy titanium alloy, aluminum alloy, etc., of which carbon steel is the most widely used body material. ASTM A216 WCA, WCB and WCC are suitable for medium and high-pressure valves with a working temperature between -29 and 425℃. GB 16Mn and 30Mn are used under the temperature between -40 and 450℃, are commonly used alternative materials like ASTMA105. Both contain 0.25 Carbon,  here let’s clarify the difference between WCB and A105 valves:

  1. Different materials and standards

Carbon steel for A105 valves means forged steel in ASTM A105 standard. A105 is a common material belongs to United States standard ASTMA105/A105M and GB/T 12228-2006 (basically equivalent).

Carbon steel WCB valve belongs to ASTM A216 specification with grades WCA and WCC, which feature slight differences in terms of chemical and mechanical properties, equivalent to the national mark ZG310-570 (ZG45).

 

  1. Different molding methods

A105 valve can be forged by plastic deformation to improve the internal structure, good mechanical properties and even grain size.

WCB valves by cast liquid forming that can cause tissue segregation and defects and can be used to cast complex workpieces.

 

  1. Different performance

The ductility, toughness and other mechanical properties of A105 forged steel valves are higher than WCB castings and can bear greater impact force. Some important machine parts should be made of forged steel.

WCB cast steel valves can be divided into cast carbon steel, cast low alloy steel and cast special steel, which are mainly used to make parts with complex shapes, difficult to forge or machined and requires higher strength and plasticity.

 

In terms of the mechanical properties of materials, forgings of the same material have better performance than castings because of the denser grain structure and better airtightness but an increased cost, which is suitable for high requirements or the temperature less than 427℃, such as the pressure reducer. We recommended that A105 cover body material for small size valve or high-pressure valve, WCB material for large size valve or middle and low-pressure valve due to mold opening cost and material utilization rate of forging.

 

As a fully stocked manufacturer and distributor of the industrial valve, PERFECT provides a complete line of valves for sale that is supplied to various industries. Available valve body material including carbon steel, stainless steel, titanium alloy, copper alloys, etc and we make the material easy to find for your valve need.

 

Effect of alloy element Mo in steel

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The element Molybdenum (Mo) is a strong carbide and was discovered in 1782 by Swede chemist HjelmPJ. It usually exists in alloy steels in amounts of less than 1%. Chromium-molybdenum steel can replace chromium-nickel steel sometimes to produce some important working parts such as high-pressure valves, pressure vessels, and has been widely used in tempered carburized structure steel, spring steel, bearing steel, tool steel, stainless acid-resistant steel, heat resistant steel and magnetic steel. If you are interested, please read on.

Effect of microstructure and heat treatment of steel

1) Mo can be solidity dissolved in Ferrite, Austenite and Carbide, and is an element to reduce Austenite phase zone.

2) The low content of Mo formed the cementite with iron and carbon, and the special carbide of molybdenum can be formed when the content is high.

3) Mo improves the hardenability, which is stronger than chromium but worse than manganese.

4) Mo improves tempering stability of steel. As a single alloy element, molybdenum increases the temper brittleness of steel. When coexisting with chromium and manganese, Mo reduces or inhibits temper brittleness caused by other elements.

 

Effect on mechanical properties of steel

1) Improved the ductility, toughness and wear resistance of steel.

2) Mo has a solid solution strengthening effect on Ferrite, that improves the stability of carbide and thus improve the strength of steel.

3) Mo increases the softening temperature and recrystallization temperature after deformation strengthening, greatly increasing the creep resistance of Ferrite, effectively inhibiting the accumulation of cementite at 450~600℃, promoting the precipitation of special carbides, and thus becoming the most effective alloy element to improve the thermal strength of steel.

 

Effect on physical and chemical properties of steel

1) Mo can improve the corrosion resistance of steel and prevent pitting corrosion resistance in chloride solution FOR austenitic stainless steels.

1) When the mass fraction of molybdenum is more than 3%, the oxidation resistance of steel deteriorates.

3) The mass fraction of Mo less than 8% can still be forged and rolled, but when the content is higher, the deformation resistance of steel to hot machinability will increase.

4) In the magnetic steel with a carbon content of 1.5% and molybdenum content of 2%-3%, residual magnetic sensitivity and coercivity can be improved.

What’s the PEEK material used for?

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Polyetheretherketone (PEEK) is a high-performance polymer (HPP) invented in the United Kingdom in the late 1970s. It is regarded as one of the six major specialty engineering plastics along with polyphenylene sulfide (PPS), polysulfone (PSU), polyimide (PI), polyaromatic ester (PAR) and liquid crystal polymer (LCP).

PEEK offers excellent mechanical properties compared with other special engineering plastics. For example, it has high-temperature resistance of 260 ℃, good self-lubricity, chemical corrosion resistance, flame retardant, peel resistance, abrasion resistance and radiation resistance. It has been widely used in aerospace, automobile manufacturing, electronics and electrical, medical and food processing fields. The PEEK materials which have been reinforced and modified by blending, filling and fiber composite, have better properties. Here we will describe the application of PEEK here in details.

Electronics

PEEK materials are excellent electrical insulators and maintain excellent electrical insulation in harsh working environments such as high temperature, high pressure and high humidity. In the semiconductor industry, PEEK resin is often used to make wafer carriers, electronic insulating diaphragm and various connecting devices. It is also used in wafer carriers insulating film, connector, printed circuit board, high-temperature connector, etc.

PEEK powder coating is covered on the metal surface by brush painting, thermal spraying and other methods to obtain good insulation and corrosion resistance. PEEK coating products include household appliances, electronics, machinery, etc. It can also be used for filling column for liquid chromatographic analysis and superfine tube for connection.

Currently, PEEK materials are also used in integrated circuits made by Japanese companies. The field of electronics and electrical appliances has gradually become the second-largest application category of PEEK resin.

 

Mechanical Manufacturing

PEEK materials can also be used in petroleum/natural gas/ultra-pure water transportation and storage equipment such as pipelines, valves, pumps and volumeters. In petroleum exploration, it can be used to make specially sized probes of mining mechanical contacts.

In addition, PEEK is often used to manufacture deflector valves, piston rings, seals, and various chemical pump and valve components. It also to make the impeller of vortex pump replaced stainless steel. PEEK can still be bonded with various adhesives at high temperatures, so connectors may be another potential niche market.

 

Medical apparatus and instruments

PEEK material is not only used for surgical and dental equipment and medical instruments with high sterilization requirements but also can replace metal artificial bone. It is characterized by biocompatibility, lightweight, non-toxic, strong corrosion-resistance, etc and is a similar material with the human body in elasticity modulus. (PEEK 3.8GPa, cancellous bone 3.2-7.8Gpa and cortical bone 17-20Gpa).

 

Aerospace and aviation

PEEK’s excellent flame retardant properties allow it to replace aluminum and other metals in various aircraft components, reducing the risk of an aircraft fire.PEEK polymeric materials have been officially certified by various aircraft manufacturers and are also eligible to supply military standard products.

 

Automobile

PEEK polymeric materials have various advantages like high strength, lightweight and good fatigue resistance, are easy to be processed into components with minimal tolerance. They can successfully replace metals, traditional composites and other plastics.

 

Power

PEEK is resistant to high temperatures, radiation and hydrolysis. The wire and cable coil framework made by PEEK has been successfully used in nuclear power plants.

 

PERFECT is a fully stocked manufacturer and distributor of industrial valve and we provide a complete line of PEEK O-rings and valve seats for sale that is supplied to various industries. learn more, contact us now!

The difference between globe valve and butterfly valve

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Globe valve and butterfly valve are two common valves used to control the flow in the pipeline. The disc of the globe valve moves in a straight line along the centerline of the seat to open and close the valve. The stem axis of the globe valve is perpendicular to the sealing surface of the valve seat, and the opening or closing travel of the stem is relatively short, making this valve very suitable for cutting off or adjusting and throttling as the flow.

 

Butterfly valve’s plate-shaped disc rotates around its own axis in the body to cut and throttle the flow. The butterfly valve is characterized by its simple structure, small volume, lightweight, the composition of only a few parts, and rapid opening and closing by rotation of only 90°, fast control of fluid media, which can be used for media with suspended solid particles or powdery media. Here we’ll discuss the difference between them, if interested, please read on.

 

  1. Different structure. The globe valve is composed of the seat, disc, stem, bonnet, handwheel, packing gland, and etc. Once opening, there is no contact between the valve seat and the sealing surface of the disc. The butterfly valve is mainly composed of valve body, stem, butterfly plate and sealing ring. The valve body is the cylindrical, short axial length, it’s open and close is usually less than 90°, when in fully open, it offers a small flow resistance. Butterfly valve and butterfly rod do not have self-locking ability. For the consideration of butterfly plate, a worm gear reducer should be installed on the valve stem. Which can make butterfly plate have self-locking ability to stop butterfly plate in any position and improve the operational performance of valve.
  2. It works differently. The globe valve raises the stem when it opens or closes, meaning that the handwheel rotates and lifts along with the stem. For butterfly valve, disc-shaped butterfly plate in the body around its own axis rotation, so as to achieve the purpose of opening and closing or adjustment. The butterfly plate is driven by the valve stem. If it rotates more than 90°, it can be opened and closed once. The flow of medium can be controlled by changing the deflection Angle of the butterfly plate. When opened in the range of about 15°~70°, and sensitive flow control, so in the field of large-diameter adjustment, butterfly valve applications are very common.
  3. Different functions. Globe valve can be used for cutting off and flow regulation. A butterfly valve is suitable for flow regulation, generally in throttling, adjustment control and mud medium, short structure length, fast opening and closing speed (1/4 Cr). The pressure loss of the butterfly valve in the pipe is relatively large, about three times that of gate valve. Therefore, when selecting a butterfly valve, the influence of pressure loss of the pipeline system should be fully considered, and the strength of the butterfly plate bearing pipeline medium pressure should also be considered when closing. In addition, consideration must be given to the operating temperature limitations of the resilient seat material at high temperatures.
  4. The industrial butterfly valve is usually a large diameter valve used for high-temperature medium smoke duct and gas pipeline. The small valve structure length and overall height, fast opening and closing speed, making it has a good fluid control. When the butterfly valve is required to control the flow of use, the most important thing is to choose the right specifications and types of butterfly valve, so that it can be appropriate, effective work.

 

In general, a globe valve is mainly used for the open/close and flow regulation of small diameter pipe (branch pipe) or pipe end, the butterfly valve is used for open and close and flow regulation of branch pipe. Arrange by switch difficulty: stop valve > butterfly valve; Arranged by resistance: globe valve > butterfly valve; by sealing performance: globe valve > butterfly valve and gate valve; By price: globe valve > butterfly valve (except special butterfly valve).