PTFE lined valve VS PFA lined valves

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Lined valves are a safe and reliable solution to any level of corrosion flow for chemical industrial. The lining of the valves and fittings ensures extremely high chemical resistance and longevity. PTFE lined valve and PFA lined valves are the commonly used valves that used as more economic alternatives to high-grade alloys in corrosive applications in the chemical, pharmaceutical, petrochemical, fertilizer, pulp and paper, and metallurgical industries. To know their difference, you must to know the material differences between PTFE and PFA.

Both of PFA and PTFE are the commonly used forms of Teflon. PFA and PTFE have similar chemical properties: excellent mechanical strength and stress-cracking resistance. The features of good molding performance and wide processing range made it’s suitable for molding, extrusion, injection, transfer molding and other molding processing, can be used for making wire and cable insulation sheath, high-frequency insulation parts, chemical pipelines, valves and pumps corrosion-resistant lining; Machinery industry with special spare parts, textile industry with a variety of anticorrosive materials electrode, and so on.

PTFE (Teflon) is a polymer compound formed by the polymerization of tetrafluoroethylene with excellent chemical stability, corrosion resistance, sealing, high lubrication and non-viscosity, electrical insulation and good aging resistance for media such as strong acid, strong alkali, strong oxidant. Its operating temperature is -200 ~ 180℃, poor fluidity, large thermal expansion. PTFE Lined valves ensures extremely high chemical resistance and longevity, can be widely used in corrosive applications in the chemical, electric machinery， pharmaceutical, petrochemical, fertilizer, pulp and paper, and metallurgical industries.

PFA (Polyfluoroalkoxy) is a high-performance thermoplastic material with improved viscosity developed from PTFE. PFA has similarly excellent performance as PTFE but superior to PTFE in terms of flexibility, which is the more popularly known form of Teflon. What distinguishes it from the PTFE resins is that PFA is melt processable. PFA has a melting point of about 580F and a density of 2.13-2.16 (g/cm3). Its service temperature is -250 ~ 260 ℃, it can be used for up to 10000h even at 210 ℃. It features excellent chemical resistance, resistance to any strong acid (including water), strong alkali, grease, insoluble in any solvent, excellent aging resistance, almost all viscous substances can not adhere to its surface, completely no combustion. Tensile strength (MPa) > 23, elongation (%) > 250.

In general, the combined performance of PFA lined valves is much better than PTFE lined valves. PTFE valve is more common and popular due to its cheaper cost, PFA is more often used in industrial applications, particularly industrial tubing and valves. PFA lined valve guarantees high sealing performance in the large range of pressure and temperature difference and is suitable for transportation of liquid and gas media in various industrial pipelines, such as sulfuric acid, hydrofluoric acid, hydrochloric acid, nitric acid and other highly corrosive media.

We offer the lined ball valve, plug valves and gate valves that are leak-free and have minimal operating and maintenance costs. In addition to the standard PTFE lining, we can also offer anti-static lining from PFA. If you’d like to find out more information, call us today!.

 

Development of high pressure critical hydrogen valve

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Recently, PERFECT factory produced a small batch of high-pressure hydrogenation valves. High-pressure hydrogenation is an important process in petroleum deep processing and coal chemical industry. It can not only improve the recovery rate of crude oil but also improve the quality of fuel oil. The dielectric environment of a high-pressure hydrogenation device is characterized by high pressure and hydrogen (with hydrogen sulfide), with flammable and explosive high-pressure gases (hydrogen or hydrocarbon + hydrogen) which store large pressure energy. Once its storage and transportation equipment (including pipeline valves) damage will cause a catastrophic safety accident.

Hydrogen can cause a number of different adverse effects in metallic materials. It can penetrate into the metal material and cause material embrittlement and deformation at normal temperature. Hydrogen sulfide corrosion of metal materials is a very difficult problem, it can cause stress corrosion cracking of metal materials at room temperature and high temperature. All these features have required a strict need for material, structural design and strength design of high-pressure hydrogenation valve. Therefore, the high-pressure hydrogenation valve must face the problems of hydrogen embrittlement and hydrogen corrosion and must pay attention to the problem of leakage under high-temperature and high-pressure conditions. Valves with high-pressure hydrogenation, generally including ball valves, gate valves, globe valves, check valves and plug valves, ASME CL900~2500, room temperature to 400℃.

Valves used in industrial hydrogen applications like petrochemical processes are often made of Cr-Mo steel and Inconel alloy. The main materials of high-pressure hydrogenation valve are A182 F11/F22/F321, A216 WCB, A217 WC6 / WC9, A351 CF8C, Inconel 725 with a diameter DN15-400 mm.

The design and manufacture of hydrogenation valves shall conform to API 600, API 602, BS 1868, BS 1873, ASME B16.34, NACE MR0175, NACE MR0103 and this standard. Our manufacturing center has the ability to produce high-pressure hydrotreating valves and has been successfully applied in hydrotreating equipment (operating pressure 8~10 MPa). More information, call for us today!

Rising stem gate valve VS non-rising stem gate valve

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Gate valve is a kind of valve for medium connection and shut- off but not suitable for regulating. Compared with other valves, gate valves have a wider range of combined applications for pressure, service fluid, design pressure and temperature. According to the screw position of the stem, the gate valve can be divided into rising stem gate valves and Non-rising stem gate valve (NRS).

Stem nut for open stem gate valve is on its cover. Rotation of stem nut drives stems up and down when opening or closing gate valve. It opens and closes the disc connected to the stem by lifting or lowering the thread between the handwheel and the stem and fully open position does not disrupt the flow. This design is favorable to the lubrication of the valve stem and has been widely used. The wedge is rubber coated and It is not used as a check valve and flow rate adjustments.

 

The advantages disadvantages of rising stem gate valve：

  • Easy to open and close.
  • Small fluid resistance, sealing surface by medium erosion and erosion.
  • Medium flow is not restricted, no turbulence, no pressure reduction.
  • The sealing surface is easy to be eroded and scraped, difficult for maintenance.
  • Larger structure requires more space and long-time opening.

 

Non-Rising Stem means outside stem, also referred to as the rotary stem gate valve or blind stem wedge gate valve. In an NRS valve, the stem will turn to open and close the gate, but the stem does not move up or down as it turns. As the stem turns, it moves into or out of the valve, which also moves the gate to open or seal the valve.

The advantages and disadvantages of non-rising stem gate valve：

  • Non-rising stem valves take up less space, ideal for gate valve with limited space. Generally, an open-close indicator should be installed to indicate the degree of open-close.
  • Failure to lubricate stem threads will result in medium erosion and easy damage.

 

What’s the difference between rising stem gate valve and non-rising stem gate valve?

  1. Appearance: The rising stem gate valve can be seen from the appearance whether the valve is closed or open. The lead screw can be seen while the non-rising stem gate valve cannot.
  2. The ascension screw of rising stem flanged gate valve is exposed outside, the nut cling to the handwheel is fixed (not rotating axial movement), the rotation of the screw and gate only relative motion without relative axial displacement of the disc and stem up and down together. The lifting screw of the non-rising stem flange gate valve only rotates and does not move up and down.

Bolt strength grades marking for valve

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A bolt is a cylindrical body with external threads consisting of a head and a screw. As one of the most commonly used fasteners, it is used in conjunction with a nut to connect two parts with holes like valves. The bolts used for valve flange connection can be classified into 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9 and etc. The bolts of class 8.8 and above are called high-strength bolts which made of low or medium carbon alloy steel after heat-treated (quenched and tempered). Bolt grades are composed of two numbers and a decimal point, which respectively represent the nominal tensile strength value and bending strength ratio of bolt material, where the first number multiplied by 100 represents the nominal tensile strength of the bolt; These two numbers are multiplied by 10 to give the bolt its nominal yield point or yield strength.

 

A strength rating of 4.6 bolt means:

  1. Nominal tensile strength reaches 400MPa;
  2. The bending strength ratio is 0.6;
  3. Nominal yield strength reaches 400×0.6=240 MPa

Strength grade 10.9 high strength bolt, indicating that the material can achieve the following after heat treatment:

  1. Nominal tensile strength up to 1000 MPa;
  2. The bending ratio is 0.9;
  3. Nominal yield strength reaches 1000×0.9=900 MPa

Bolt strength grade is an international standard. Strength grades 8.8 and 10.9 refer to shear stress grades 8.8 and 10.9 GPa for bolts.8.8 nominal tensile strength 800 N/MM2 nominal yield strength 640N/MM2. The letter “X.Y” indicates the strength of the bolt, X*100= the tensile strength of the bolt, X*100*(Y/10)= the yield strength of the bolt (as specified: yield strength/tensile strength =Y/10). For example, the tensile strength of class 4.8 bolts is 400MPa; Yield strength: 400*8/10=320MPa. But there are exceptions, such as stainless steel bolts are usually labeled A4-70, A2-70.

 

Bolt grade marking and corresponding material selection:

Strength class

 Recommend material

Minimum tempering temperature
3.6 Low carbon alloy steel 0.15%≤C≤0.35%  
4.6 Medium carbon steel 0.25%≤C≤0.55%  
4.8  
5.6  
5.8  
6.8  
8.8 Low Carbon Alloy Steel with 0.15%<C<0.35% 425
Medium carbon steel 0.25%<C<0.55% 450
9.8 Low Carbon Alloy Steel 0.15%< C < 0.35%  
Medium Carbon Steel 0.25%<C<0.55%
10.9 Low Carbon Alloy Steel with 0.15%<C<0.35% 340
Medium carbon steel 0.25%<C<0.55% 425

We are a fully stocked manufacturer and distributor of the flanged connected ball valve, bolted bonnet globe valve and we make the valve easy to find for your need. When installing and removing the valves, bolts should be tightened symmetrically, step by step and evenly. These valves bolt selection should refer to the following chart:

Valve DN Screw hole diameter(mm) Nominal bolt diameter(mm) Bolt number Valve thickness   (mm) Flange thickness        (mm) Nut

(mm)

 Spring gasket (mm) Single screw length (mm) Bolt size
DN50 18~19 M16 4 0 20 15.9 4.1 68 M16*70
DN65 18~19 M16 4 0 20 15.9 4.1 68 M16*70
DN80 18~19 M16 8 0 20 15.9 4.1 68 M16*70
DN100 18~19 M16 8 0 22 15.9 4.1 72 M16*70
DN125 18~19 M16 8 0 22 15.9 4.1 72 M16*70
DN150 22~23 M20 8 0 24 19 5 80 M20*80
DN200 22~23 M20 12 0 26 19 5 84 M20*90
DN250 26~27 M22 12 0 29 20.2 5.5 91.7 M22*90
DN300 26~27 M22 12 0 32 20.2 5.5 97.7 M22*100
DN350 26~27 M22 16 0 35 20.2 5.5 103.7 M22*100

 

 

The material for high temperature industrial valve

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Working temperature is a key factor should be taken into consideration for valve design, manufacture and inspection. Generally, the operating temperature t > 425℃ valve is referred to as a high-temperature valve, but the number is difficult to distinguish the temperature range of high temp valve. High temp valve including high temp gate valve, high temperature globe valve, high temperature check valve, high temperature ball valve, high temperature butterfly valve, high temperature needle valve, high temperature throttle valve, high temperature pressure reducing valve. Among them, the most commonly used are gate valve, globe valve, check valve, ball valve and butterfly valve. High temp valves are widely used in petrochemical, chemical fertilizer, electric power and metallurgy industries. According to ASME B16.34, the material of the valve body and interior part are different in each temperature range. In order to ensure the valve in accordance with its corresponding high temp working conditions, it is absolutely necessary to scientifically and reasonably design and distinguish the high temp level of valve.

Some high temp valve manufacturers divide high temperature valves into five grades according to temp rating based on its production experience. That is, the valve operating temperature t>425~550℃ is grade PI, t>550~650℃ is grade PII, t>650~730℃ is grade PIII, t>730~816℃ is grade PIV, and t>816℃ is grade PV. Among them, PI~PIV valve mainly depends on the selection of appropriate materials to ensure its performance, PV valve in addition to material selection is more important to use special design such as lining insulation lining or cooling measures. High-temperature valve design should pay attention to the use of temperature shall not exceed the maximum allowable use temperature of the material. According to ASMEB31.3, the maximum temperature of common high-temperature valve materials is shown in the following table. Special note is that in the actual design of the valve also consider the corrosive medium and stress levels and other factors, the allowable temperature of the valve material is actually lower than the table.

 

Pressure-temperature rating for commonly used stainless steel:

Workworn temp  Material Pound class working pressure, pounds per square inch
150 300 400 600 900 1500 2500 4500
800℉

(427℃)

 CF8, 304, 304H 80 405 540 805 1210 2015 3360 6050
CF8M, 316, 316H 80 420 565 845 1265 2110 3520 6335
321, 321H 80 450 600 900 1355 2255 3760 6770
CK-20, 310, 310H 80 435 580 875 1310 2185 3640 6550
1000℉

(538℃)

 CF8, 304, 304H 20 320 430 640 965 1605 2625 4815
CF8M, 316, 316H 20 350 465 700 1050 1750 2915 5245
321, 321H 20 355 475 715 1070 1785 2970 5350
CK-20, 310, 310H 20 345 460 685 1030 1720 2865 5155
1200℉

(650℃)

 CF8, 304, 304H 20(1) 155 205 310 465 770 1285 2315
CF8M,316,316H 20(1) 185 245 370 555 925 1545 2775
321, 321H 20(1) 185 245 365 555 925 1545 2775
CK-20, 310, 310H 20(1) 135 185 275 410 685 1145 2055
1350℉

(732℃)

 CF8, 304, 304H 20(1) 60 80 125 185 310 515 925
CF8M, 316, 316H 20(1) 95 130 190 290 480 800 1440
321, 321H 20(1) 85 115 170 255 430 715 1285
CK-20, 310, 310H 20(1) 60 80 115 175 290 485 875
1500℉

(816℃)

 CF8, 304, 304H 10(1) 25 35 55 80 135 230 410
CF8M, 316, 316H 20(1) 40 55 85 125 205 345 620
321, 321H 20(1) 40 50 75 115 190 315 565
CK-20, 310, 310H 10(1) 25 35 50 75 130 215 385

 

Pressure – temperature rating of Cr – Mo high-temperature steel

Working temp Grades Pound class working pressure, pounds per square inch
150 300 400 600 900 1500 2500 4500
800℉

(427℃)

 WC4, WC5, F2 80 510 675 1015 1525 2540 4230 7610
WC6, F11C1.2, F12C1.2, 80 510 675 1015 1525 2540 4230 7610
WC9, F22C1.3 80 510 675 1015 1525 2540 4230 7610
C5, F5 80 510 675 1015 1525 2540 4230 7610
1000℉

(538℃)

 WC4, WC5, F2 20 200 270 405 605 1010 1685 3035
WC6, F11C1.2, F12C1.2, 20 215 290 430 650 1080 1800 3240
WC9, F22C1.3 20 260 345 520 780 1305 2170 3910
C5, F5 20 200 265 400 595 995 1655 2985

 

In short, high temp valve with the operating temperature higher than 425℃, the main material of which is alloy steel or stainless steel or Cr-Ni heat resistant alloy. Actually, in practice application, the material WCB(or A105) is also widely used in the main body of the valve, such as high-temperature ball valve, check valve and butterfly valve. When the working temperature of the ball valve with PTFE and rubber as sealing ring is higher than 150 ~ 180℃, it is not recommended to use the counterpoint polystyrene seat (working temperature t≤320℃) or metal seat, that is proper “high-temperature ball valve”.

What’s the Water hammer effect of valve?

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When a valve is closed suddenly, the inertia of the pressurized flow creates a water shock wave that can cause damage to the valve or piping system. This is known as the “water hammer effect” in hydraulics or positive water hammer. On the contrary, the sudden opening of the closed valve can also produce water hammer effect, known as negative water hammer, which has a certain destructive force but is not as large as the positive water hammer.

The closing part is suddenly sucked into the seat when the valve is to close, it is called the cylinder blocking effect. This is caused by a low-thrust actuator that does not have enough thrust to remain close to the seat, causing the valve to suddenly close, creating a water hammer effect. In some cases, quick-opening flow characteristics of the control valve can also lead to the water hammer effect.

The water hammer effect is extremely destructive: too high pressure will cause the pipe and valves to breakage, and too low pressure will cause collapse, damaging valves and fixtures. It also makes a lot of noise, but the real damage to valves and piping are caused by mechanical failure. Because kinetic energy changes rapidly into static pipe pressure, water hammers can break through the pipe or damage pipe supports and joints. For valves, water hammer can produce severe vibration through the spool, which may lead to failure of the core, gasket or packing.

When the power is cut off and the machine stops, the potential energy of the pump water system will overcome the inertia of the motor and make the system stop sharply, which will also cause pressure impact and water hammer effects. To eliminate the serious consequences of the water hammer effect, any sudden pressure changes in the system must be prevented. In the pipeline need to prepare a series of buffer measures and equipment such as water hammer eliminator, water hammer pump station, straight water hammer pump.

To prevent pressure fluctuations, the valve should be closed at an even rate. For control valves that must be throttled when close to the seat, an actuator with a sufficiently large output thrust, such as a piston pneumatic or hydraulic actuator, or a special notch in the travel sleeve of a manually rotating operator, should be used to reduce or prevent cylinder blocking effects. Installing certain types of anti-surge equipment in the pipeline system can also reduce water hammer effects such as pressure relief valves or buffer drums. In addition, gas injection into the system reduces fluid density and provides some compressibility to handle any sudden fluctuations.