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).

The valve pressure class conversion of Mpa，LB，K，bar

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PN, Class, K, bar are all units of pressure rating to express the nominal pressure rating for pipelines, valves, flanges, pipe fittings or fittings. The difference is that the pressure they represent corresponds to different reference temperatures. PN refers to the corresponding pressure at 120℃, while CLass refers to the corresponding pressure at 425.5℃. Therefore, the temperature should be taken into account in pressure conversion.

PN is mostly used in European standard systems such as DIN, EN, BS, ISO and Chinese standard system GB. Generally, the number behind “PN” is an integer number denoting pressure classes, approximately equivalent to normal temperature pressure Mpa. For valves with carbon steel bodies, PN refers to the maximum allowable working pressure when applied below 200℃; For cast iron body, it was maximum allowable working pressure when applied below 120℃; For stainless steel valve body, it was maximum allowable working pressure for service below 250℃. When operating temperature increases, meanwhile the valve body pressure decreases. Commonly used PN pressure range is (unit of Bar): PN2.5, PN6, PN10, PN16, PN25, PN40, PN63, PN100, PN160, PN250, PN320, PN400.

Class is the common valve pressure rating unit of the American system, such as Class150 or 150LB and 150#, which all belong to the American standard pressure rating, representing the pressure range of pipeline or valve. Class is the calculation result of the binding temperature and pressure of a certain metal according to ANSI B16.34 standard. The main reason pound classes do not correspond to nominal pressures is that their temperature benchmarks are different. The pressure of a gas is referred to as a “psi” or “Pounds per square inch”.

Japan mainly use the unit of K to indicate the pressure level. There is no strict correspondence between nominal pressure and pressure grade due to their different temperature reference. The approximate conversion between them is shown in the table below.

 

The conversion table between Class and Mpa

Class 150 300 400 600 800 900 1500 2000 2500
Mpa 2.0 5.0 6.8 11.0 13.0 15.0 26.0 33.7 42.0
Pressure rating medium medium medium high high high high high high

 

The conversion table between Mpa and bar

0.05(0.5) 0.1(1.0) 0.25(2.5) 0.4(4.0) 0.6(6.0) 0.8(8.0)
1.0(10.0) 1.6(16.0) 2.0(20.0) 2.5(25.0) 4.0(40.0) 5.0 (50.0)
6.3(63.3) 10.0(100.0) 15.0(150.0) 16.0(160.0) 20.0(200.0) 25.0(250.0)
28.0(280.0) 32.0(320.0) 42.0 (420.0) 50.0(500.0) 63.0(630.0) 80.0(800.0)
100.0(1000.0) 125.0(1250.0) 160.0(1600.0) 200.0(2000.0) 250.0(2500.0) 335.0(3350.0)

 

The conversion table between lb and K

Lb 150 300 400 600 900 1500 2500
K 10 20 30 40 63 100 /
Mpa 2.0 5.0 6.8 10.0 15.0 25.0 42.0

 

Why the open and closure is difficult for large caliber globe valve?

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Large diameter globe valves are mostly used for media with big pressure drop such as steam, water, etc. Engineers may face the situation, that the valve is often difficult to close tightly and prone to leakage, which is generally due to the valve body design and insufficient horizontal output torque (adults with different physical conditions have the horizontal limit output force of 60-90k). The flow direction of the globe valve is designed to be low-enter and high -exit. Manual pushes the handwheel to rotate so that the valve disc moves downward to close. At this time, the combination of three forces needs to be overcome:

1) Fa:  Axial jacking force;

2) Fb: Packing and stem friction;

3) Fc: Friction force Fc between the valve stem and disc core;

The sum of the torques∑M=(Fa+Fb+Fc)R

We can draw the conclusion that the larger the diameter is, the larger the axial jacking force is and the axial jacking force is almost close to the actual pressure of the pipe network when it is closed. For example, a DN200 globe valve is used for the steam pipe of 10bar, it only closes the axial thrust Fa=10×πr²==3140kg, and the horizontal circumferential force required for closing is close to the limit of the horizontal circumferential force output by the normal human body, so it is very difficult for a person to completely close the valve under this condition. It is recommended that this type of valve be reversely installed to solve the problem of difficult closing but produce the difficult-opening at the same time. Then there is a question, how to solve it?

1) It is recommended to choose bellows sealing globe valve to avoid the impact of friction resistance of the plunger valve and packing valve.

2) The valve core and valve seat must choose the material with good erosion resistance and wear performance, such as castellan carbide;

3) Double disc structure is recommended to avoid excessive erosion due to a small opening, which will affect the service life and sealing effect.

 

Why the large diameter globe valve is easy leakage?

The large-diameter globe valve is generally used in boiler outlet, main cylinder, main steam pipe and other parts, which are prone to produce the following problems:

1) The pressure difference at the outlet of the boiler and the steam flow rate are both large, both have great erosion damage on the sealing surface. In addition, the inadequate combustion of the boiler makes the steam at the outlet of the boiler water content is large, easy to damage the sealing surface of the valve such as cavitation and corrosion.

2）For the globe valve near the boiler outlet and cylinder, intermittent overheating phenomenon may be in the fresh steam during the process of its saturation if the boiler water softening treatment is not too good often precipitate part of  the acid and alkali substances, the sealing surface will cause corrosion and erosion; Some crystallizable substances may also adhere to the valve seal surface crystallization, resulting valve cannot be tightly sealed.

3) Due to the uneven amount of steam required by the production of valves at the inlet and outlet of the cylinder, evaporation and cavitation are easy to occur when the flow rate changes greatly, and damage to the sealing surface of the valve, such as erosion and cavitation.

4）The pipe with large diameter needs to be preheated, which can allow the steam with the small flow to be heated slowly and evenly to a certain extent before the globe valve can be fully opened, so as to avoid excessive expansion of the pipe with rapid heating and damage the connection. But the valve opening is often very small in this process, so that the erosion rate is far greater than the normal use effect, seriously reduce the service life of valve sealing surface.