Securing Critical Processes: The Importance of Severe Service Valves

Metal-seated, zero-leakage, severe service valves are specialized solutions for various industries most demanding and challenging applications. These valves provide exceptional performance, reliability, and safety in environments where traditional valves may fail to meet stringent requirements. Their unique design and advanced features make them essential components in oil and gas, chemical processing, power generation, and more.

The primary characteristic of metal-seated, zero-leakage, severe service valves is their ability to achieve a perfect seal, even under extreme conditions. Unlike conventional valves that may use soft seats or elastomeric materials, these valves employ superior metal-to-metal seating surfaces. The metal seats are precision-machined and often coated with advanced materials like stellite or tungsten carbide to enhance their durability and resistance to wear corrosion, and erosion. This metal-to-metal seating ensures a tight seal, preventing fluid or gas leakage, even at high temperatures and pressures.

Zero leakage is a critical requirement and a responsibility in many industrial applications, particularly in the oil and gas sector. Leakage of hydrocarbons or other hazardous fluids can lead to severe environmental contamination, safety risks, and significant financial losses. Metal-seated, zero-leakage valves address this issue by providing a reliable and long-lasting solution. They are designed to maintain their sealing integrity even after numerous cycles and in the presence of abrasive or corrosive media. This level of performance is essential in downstream processing, where the slightest leakage can disrupt operations and compromise product quality.

In addition to their zero-leakage capabilities, severe service valves withstand extreme operating conditions. Depending on the specific application requirements, they use high-strength, heat-resistant materials such as stainless steel, nickel alloys, or titanium. These materials enable the valves to handle high temperatures, pressures, and aggressive media without failure or degradation. The robust construction also allows for a longer service life, reducing the need for frequent maintenance and replacements.

Severe service valves find applications in various critical processes across industries such as steam systems, boiler feedwater control, and turbine bypass applications in the power generation sector. The valves' ability to handle high-temperature steam and maintain tight shutoff is crucial for efficient and safe power plant operations. In the chemical processing industry, severe service valves apply in reactor systems, high-pressure fluid handling, and corrosive environments. They ensure process integrity, prevent leakage of toxic chemicals, and contribute to the plant's overall safety.

The oil and gas industry relies heavily on metal-seated, zero-leakage, severe service valves throughout its upstream, midstream, and downstream operations. These valves are vital in ensuring smooth and safe operations, from wellhead control and pipeline isolation to refinery processes and gas processing plants. They handle the extreme pressures, temperatures, and abrasive nature of hydrocarbons, providing reliable flow control and isolation capabilities.

In conclusion, metal-seated, zero-leakage, severe service valves are indispensable components in industries that demand the highest performance, reliability, and safety levels. Their unique design, materials construction, and zero-leakage capabilities make them the preferred choice for handling extreme conditions and critical applications. By investing in these advanced valve solutions, industries can mitigate risks, improve process efficiency, and ensure compliance with stringent environmental and safety regulations.

Mead O'Brien
https://meadobrien.com
(800) 874-9655

ValvTechnologies RiTech® Coating an Excellent Alternative for Applications Where Stellite Disbonding a Concern

Stellite is a trademarked name of Kennametal Inc. describing a range of cobalt-chromium alloys designed for wear resistance. Commonly used on severe service valves, Stellite alloys operate at high temperatures (600 – 1112° F), can be polished to excellent levels of surface finish producing low friction coefficients and in-turn providing good sliding wear. In high-temperature, high-pressure steam applications, however, there are reported issues of Stellite delamination when valves operate at Stellite's upper operating temperature range.

Table of ValvTechnologies RiTech Coatings
(Click for larger view)

ValvTechnologies, a manufacturer of severe service valves, offers their RiTech® coatings and process as a better alternative to Stellite for these applications.

ValvTechnologies' RiTech® is a high-velocity oxygen fuel (HVOF), hot, high-velocity, gas jet coating process. RiTech® 31 is an alloy that maintains its hardness at high temperatures and is self-repairing in operation.

The article below, written by the editors of the Combined Cycle Journal and distributed by ValvTechnologies, explains the reported Stellite delamination problems as well as a RiTech® 31 user experience.

For more  information about ValvTechnologies valves and RiTech® 31, contact Mead O'Brien by calling (800) 892-2769 or by visiting https://meadobrien.com.

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Coating Critical Steam-valve Parts with Chrome Carbide Avoids Stellite Delamination Issue

The original article can be found here on the Combined Cycle Journal site. 

Stellite liberation from large valves installed in main and hot reheat (HRH) steam systems serving F-class combined cycles, considered a major industry problem 10 years ago, has been eliminated by substituting chrome carbide as the hard-facing material for critical valve parts.

The editors first learned of stellite delamination at the 2009 7F Users Group Conference where the liberated material from a 20-in. HRH block valve was displayed. The industry had been made aware of stellite liberation by GE, which issued Technical Information Letter 1626 about three months ahead of the 7F meeting. It advised steam-turbine owners to check the condition of the stellite inlay sections used in fabricating seats for the OEM’s combined stop and control valves.

Revision 1 of that TIL, published at the end of 2010, recommended a “one-time seat stellite inlay UT inspection during valve installation or the next planned maintenance inspection”—this to identify any lack of bonding between the inlay and base metal on units with fewer than 50 starts.

Disbonding of stellite associated with combined-cycle plants has occurred primarily in parallel-slide gate valves and non-return globe valves. Hardfacing has been liberated from valve seats, guide rails, and discs. Tight shutoff of valves has been compromised in some cases.

Many incidents of stellite liberation were reported. To illustrate: CFM/VR-TESCO LLC (formerly Continental Field Machining), a leading valve services company said that in 2011 and 2012 it repaired 50 valves manufactured from F91 (forged body) or C12A (cast body) and ranging in size from 12 to 24 in. More than half of these jobs involved stellite liberation.

These repair projects were split roughly 50/50 between valves within the Code (ASME Boiler & Pressure Vessel Code) boundary and those that were part of the boiler external piping. Repairs on the former were performed according to guidelines presented in Section I of the Code and in the National Board Inspection Code; those outside the Code boundary were performed according to ASME B31.1.

There hasn’t been much discussion on stellite disbonding the last few years—at least at meetings attended by the editors, which include the Combined Cycle Users Group, Steam Turbine Users Group, and HRSG Forum with Bob Anderson.

However, mention was made by one owner/operator regarding the successful use of ValvTechnologies Inc.’s IsoTech® parallel-slide gate valves on his company’s HRSGs in eliminating the need for stellite. According to the manufacturer, critical parts for its severe-service valves, used where steam temperatures exceed 1000F, are provided with its RiTech® 31 coating.

This chrome carbide refractory coating is much harder than Stellite 6 (68-72 RC versus 34-38 RC). It is applied in state-of-the-art HVOF (high-velocity oxygen fuel) spray booths using a proprietary compressive spray technique to achieve high bond strength. Applications extend up to ASME/ANSI Class 4500 at 1800F for valves up to 36 in.

The chrome carbide hard-coated web guide ensures the discs are kept parallel through the entire valve stroke. As the valve is cycled under differential pressure, the hard surfaces reportedly burnish and polish each other, avoiding the scratching and galling cited by some others.

The user sharing his experience with the ValvTechnologies product said their parallel slide gate valves have been operating on four or five of his company’s HRSGs for three years or so and the only hiccup was a stem-packing leak on one valve which was quickly corrected. This testifies to the vendor’s claim that RiTech 31 hard-coating technology is impervious to the effects of high-temperature cycling typically experienced today in combined-cycle main-steam isolation and HRH applications. The company guarantees coating integrity for 10 years or 10,000 cycles—whichever comes first.

Finally, the user mentioned that a representative of the manufacturer annually visits each plant where ValvTechnologies valves are installed to verify that they continue to meet expectations.

Courtesy of Combined Cycle Journal. Combined Cycle Journal is the independent voice of the gas-turbine-based generation sector of America’s electricity industry.