Web Avatar Logo

Ladish Valve Seating, Test Standards, Seating Material

Content provided by Barry Hoeffner

Since 1961, Ladish has been the premier manufacturer of Stainless Steel, Alloy 20, Duplex, Nickel and Exotic Alloy Industrial valves. Product line includes Gate, Globe, Check and Ball Valves. With size ranges from .5” – 30”, & Classes 150 –  2500. we are well equipped to meet your valve needs.

Ladish is known for:

  • Standard and Specialty Engineered Products
  • Local Manufacturing and Testing
  • ISO 9001 Certified
  • PED /CE
  • Q1 & API 6D Certified


Valve Sealing

  • 90+% of Valve Inquiries / Orders in the USA call out for through-leakage to meet API 598. Does this meet the real requirement of the customer?
    • Standard API 598 Testing of Soft Seated Valves is only with Low Pressure Air following Hydro Shell Testing. High Pressure Testing is Optional and can damage seats.
    • The Leak Requirements are good, but test duration is very short. Some Customers required extended time.
  • Key Question: For Specialty (High Value) Valves, what is the required Leakage Rate and How Should it be measured?
    • Does The Customer Know?
    • Is the requirement to seal on small molecules (Hydrogen)? Is so, special testing and seal requirements may be in order.

ANSI FCI 70.2 Leakage Classifications for Control Valves

Class V: 1.1 times cold working pressure allowable leakage: .005ml/min of water per inch of port diameter per psi differential.

Class VI: 50 psi air or nitrogen. Allowable leakage: 2” – 3 bpm*, 6” – 27 bpm*, 8 – 45 bpm* Allow sufficient time for leakage flow to stabilize and use a suitable measuring device.

*bpm – bubbles per min.

There is no “ZERO LEAKAGE”:

Leak Rate (std. cc/min) Reference Leak Rate Comment
1 X 10-8 1 cc every 3 years The Rate of Helium Diffusion through glass
1 X 10-7 3 cc / year Size of 3 marbles
1 X 10-6 1 cc every two days Drop of water can stop this leak for several hours
1 X 10-5 1 cc per day Soap in needed in test water to detect
1 X 10-4 1 cc every 3 hours Bubbles rise in water
1 X 10-3 4 cc per hour Easily Detectable in Shop test for short duration
1 X 10-2 A LOT! Audible Leaking

Common Leak Measurement Standards:

Valve type Common test standard
Steel gates, globes and checks API 598
Cast Iron gates API 598, MSS SP-70*
Bronze gates, globes and checks MSS SP-80*
Pressure seal valves ASME B16.34*
Steel valves larger than NPS 24” ASME B16.34*
Pipeline valves API 6D*
Cast iron globes API 598, MSS SP-85*
Cast iron checks API 598, MSS SP-71*
Cast iron plugs API 598, MSS SP-78*
Steel ball valves API 598
Steel butterfly valves API 598
Cryogenic valves BS 6364, API 598
Pressure relief valves ASME PTC 25, API 527
Control valves ISA-S75, FCI 70-2
Class V Testing:
  • The historical class V leakage criterion and test is different in character from the other leakage classes. It was developed for nuclear power-plant applications and requires a water test at a pressure differential within 5% of the maximum operating differential. It is suited for critical applications where the control valve may be closed-without a blocking valve-for a long time with high differential pressure across the seating surfaces.
  • In this application, excessive leakage can actually cause damage to the valve. Today, however, the class V test often applies to all types of control and Isolation valves-with leakage rates that fall between the class IV and class VI test.
  • For valves designed specifically for gas service, cryogenic service, or clean service, water testing becomes impractical. By including a class V test procedure for low-pressure air testing, you can accommodate a broader range of control valves and services, yet you will want to preserve the original high-pressure water for the more specialized valves for which it was originally intended.
Ball Specifications Details:

Class Design Standards

  • API 6D
  • API 608
  • ASME B16.34
  • API 607 – Fire Safe Test – Can Influence Design

Standard Seat Materials

  • PTFE (Polytetrafluoroethylene) and Enhanced Versions
  • TFM (Molecularly Enhanced PTFE)
  • TFMC (Molecularly Enhanced PTFE – Carbon Filled)
  • DEVLON (Nylon)
  • PEEK
  • METAL (Coated or Hardened)
Elastomer Seating & Sealing Materials:
  • Elastomers represent the most common material used for valve seating and seals. This is due to the outstanding sealing ability, low friction coefficient (for ball valves) and compatibility with most low temperature (<500F) processes.
  • Elastomer Selection (as with all material selection) begins with Process Compatibility. Some Selection Criteria are:
    • Temperature
    • Pressure (Mechanical compatibility)
    • Process Consideration: Will the elastomer and/or “fillers” survive in the specific process?

Ladish Seat Materials:
  • T – Virgin PTFE Polytetrafluoroethylene- Is a Fluorocarbon-based polymer. This seating material has excellent chemical resistance and low coefficient of friction. PTFE is non-contaminating and accepted by FDA for use in food services. Not recommended for liquid alkalis and fluorine.
  • F – TFM® 1600 PTFE Dyneon® TFM PTFE is a modified TFE Polymer. A second generation PTFE that maintains the exceptional chemical and heat resistance properties of first generation PTFE. It has denser polymer structure than conventional PTFE, and exhibits better stress recovery which is important for applications such as seals, seats and gaskets. Its temperature range is -100°F to 500°F (-73°C to 260°C)
  • R – Reinforced Polytetrafluoroethylene (RTFE) PTFE’s mechanical properties are enhanced by adding percentage of Fiberglass filler material to provide improved strength, stability and wear resistance.
    • Do NOT use if there is a possibility of HF Acid
  • C – Carbon Filled TFM – This is a Teflon base filled with carbon fiber and graphite. It has a lower thermal contraction-expansion than PTFE and is ideal for steam or thermal fluid applications up to 550°F (288°C). Allows higher P/T usage.
    • Avoid “Sticky” Applications above 450 degrees F
  • P- PEEK (Unfilled) Polyetheretherketone  Peek Polymer offers a unique combination of chemical, mechanical and thermal properties. Excellent for water and steam application at elevated temperatures up to 600°F and pressures up to 6000 PSIG
    • Not Good in Nitric or HF Acid. Limited application in Sulfuric and Hydrochloric Acid
    • Do NOT Use in Oxidizer Service such as Chlorine, Fluorine or Bromine
    • Increases Torque Requirements up to 50%
  • K- KEL-F® Polychlorotrifluoroethylene  (PCTFE) PCTFE is a fluorocarbon based polymer. It offers a unique combination of physical and mechanical properties non-flammability, chemical resistance, and near zero moisture absorption. It has a temperature range of -425ºF to 400°F (-240ºC to 204°C) which is suitable for cryogenic applications.
    • Preferred Seating Material for Cryogenic Applications below -200F
    • Increases Torque Requirements 20% – 30%

Ladish MEGA Seal Graphite Seated Valves:
  • Available in 1” – 8” Valve sizes, Class 300 and 600.
  • Ladish is currently stocking the Graphite seats with Hastelloy C276 Seat “Carriers” up through 4” size.
  • Operating temperatures to 1000 degrees F
  • A fantastic alternative to Metal Seats when T/P and/or corrosive service are the drivers.

Metal Seated Valves
  • Metal-Seated Valves Represent the fastest growing (by %) segment of the Valve Industry. These seats can be found in Ball Valves, Butterfly Valves, Plug Valves and others.
  • What are “Metal Seats”:
  • Dissimilar Metals (Old Technology no longer widely accepted)
  • Base Metal Contact (Gate and Globe Valves – Not Sliding Wear)
  • Coated or Modified Metal (Most Common)
  • Stellite Weld Overlay (Usually Stellite VI – Cobalt Based)
  • “Surface Modification” of Sealing Surfaces: Ex. Nitriding, Boronizing, etc.
  • Plating: Ex. Chromium Plating or ENP (Electroless Nickel Plating)
  • HVOF Coating: Tungsten and Chromium Carbide are the most common
  • Fused or Vacuum Deposition of “Coating” typically Tungsten Carbide
  • There is no “One size fits all” for “Metal-to-metal” sealing.  Coatings are very application dependent

For more information on seating & sealing, please contact us!

Once again, Ladish will continue To Mark Progress.

Like this article? Give it a share!

Share on facebook
Share on twitter
Share on linkedin
Share on email


281.880.8560 or 866-523-4740

7603 Bluff Point Dr. Houston, TX 77086, United States




We are excited to announce that effective November 1, 2020 we have purchased the trademarks and all assets related to Smith Valves & Diamond Gear from CNC Flow Control!