Why Does the SD61H-P58.27 Superheater Isolation Valve Use a Welded Connection?

In power plant boiler reheater and superheater systems, Hydrotest Isolation Valves are critical devices for pressure boundary isolation. Their connection method directly impacts pipeline stress distribution, operational safety, and maintenance convenience. As a core component of Ultra-Supercritical units, the SD61H-P58.27 Hydrotest Isolation Valve utilizes welded connections at both ends rather than traditional flange connections. This is a targeted engineering design for high-parameter conditions. Below are the professional answers to core industry questions.

I. Core Questions: Why Prioritize Welded Connections?

Q: What are the operating conditions for the SD61H-P58.27 in USC units? Can welded connections handle them?

A: This valve is primarily used in the main steam systems of USC thermal power units. Operating pressures reach up to 58.27MPa with temperatures exceeding 600°C. These are classic high-temp, high-pressure extreme conditions. A welded connection integrates the valve with the main header into a single, equal-strength unit. This completely eliminates the leakage vulnerabilities of flanges. It is fully compatible with ultra-high parameter operations and meets the mandatory requirements of ASME B31.1, DL/T 850, and TSG 11-2020 for ultra-high-pressure boiler piping.

Q: What are the core advantages of welded connections over flange connections in high-parameter environments?

A: Traditional flange connections have three major weaknesses under 58.27MPa pressure and cyclic thermal loads:

① Gaskets prone to creep failure and low sealing reliability;

② Bolt preload decay during thermal cycles, requiring frequent hot-tightening;

③ Potential fatigue cracking at the flange neck. Welded connections bypass these issues entirely. The core benefits are:

• Safety: No gaskets or bolts to wear out, eliminating potential leak points in ultra-high-pressure systems.
• Stress Distribution: Creates a continuous rigid structure with the main steam pipe, avoiding sudden changes in stiffness and ensuring uniform thermal expansion stress.
• Longevity: Reduces pipeline vibration response and stabilizes the load on pipe hangers/supports, effectively extending the service life of the entire system.

II. Maintenance Questions: Does Welding Affect Serviceability?

Q: Once welded, does future maintenance require cutting the pipe? Is it difficult to operate?

A: No pipe cutting is required. Maintenance is convenient. We have optimized the structure for a Weld Once, Never Remove design:

• Hydrostatic Test Phase: Internal components (valve disc, pressure rod, support plate) are loaded directly from the top of the valve body without disturbing the pipeline.
• Post-Test Operation: Internals can be removed via the upper manhole and replaced with a high-precision flow sleeve. No welding is required during this process.
• Operational Consistency: The flow sleeve's inner diameter matches the DN300/DN400 pipe (deviation ≤ ±0.5mm), resulting in near-zero pressure drop. It achieves reliable testing with zero-impact operation.

Q: How is sealing performance guaranteed after internal parts are replaced?

A: The valve body is forged from high-grade heat-resistant alloys like F91/F92, following ASME Section I standards. Internal spares (discs, seal rings, etc.) are precision-matched. Once replaced, they are compressed by the upper structural assembly to form a complete sealing system with the welded body, ensuring long-term Zero-Leakage operation.

III. Product & Compatibility: Applications for SD61H-P58.27

Q: Which units typically use the SD61H-P58.27? What is its track record?

A: Specifically designed for USC thermal units, it is used in boiler superheater and reheater systems as an isolation device for hydrostatic testing and long-term operation. It has been successfully deployed in multiple 1000MW USC units with a track record of stable operation and zero recorded leaks or failures.

Q: Are there other supporting Hydrotest Isolation Valve products for HTHP scenarios?

A: We provide a comprehensive range of hydrotest isolation valves and components. Core products include:

IV. Manufacturer: Technical Edge

Q: What are your core technical guarantees as a manufacturer?

A: As a specialist in high-pressure hydrotest isolation valves, our guarantees cover three areas:

① Material Integrity: Use of high-grade F91/F92 heat-resistant alloys with strict raw material control;

② Standard Compliance: Adherence to international and domestic standards like ASME Section I and ASME B31.1;

③ Proven Application: Years of experience with 1000MW units, ensuring products are field-tested for zero-leakage and backed by full-process technical support from selection to installation.

HKCYT-2025-12-25