Introduction
Thermal‑power and petrochemical facilities face harsh high‑temperature, high‑pressure service conditions. Ordinary carbon‑steel valves suffer creep, cracking and leakage, triggering unplanned outages. As core high-temperature alloy steel valve options, WC6 valve and WC9 alloy valve are widely adopted power station alloy valves for steam and hydrocracking pipelines. Sedelon manufactures complete WC6/WC9 valve ranges. This article compares their material performance, application limits and quality control to support reliable specification for EPC teams and valve distributors.
Differences in Core Materials between WC6 Valves and WC9 Alloy Steel
Comparison Table of Chemical Composition and Mechanical Parameters
The chemical composition directly determines the high-temperature inherent performance of the cast chromium-molybdenum alloy valve. Although WC6 and WC9 both belong to the ASTM A218 chromium-molybdenum alloy steel system, there is a significant difference in the content of chromium and molybdenum. The difference in composition leads to a clear differentiation in the high-temperature creep resistance, anti-oxidation, and anti-hydrogen embrittlement performance of the two, directly limiting the use boundary of each type of power station alloy valve.
| Comparison project | WC6 valve (1.25Cr – 0.5Mo) | WC9 alloy steel valve (2.25Cr – 1Mo) Execution |
| material standards | ASTM A217 WC6 | ASTM A217 |
| WC9 Chromium content | 1.00 – 1.50% | 2.00 – 2.75% |
| Molybdenum content | 0.45 – 0.65% | 0.90 – 1.20% |
| Minimum tensile strength | 485 MPa | 485 MPa |
| Minimum yield strength | 275 MPa | 275 MPa |
| Long-term maximum operating temperature | Maximum 538 °C (1000 °F) | Maximum 593 °C (1100 °F) |
| Recommended heat treatment process | Normalizing + tempering, tempering ≥ 595 °C | Normalizing + tempering, tempering ≥ 675 °C |
The mechanical strength index of WC6 and WC9 is very close at room temperature, and the real performance gap is concentrated in the long-term continuous high-temperature pressure condition. The chromium element enhances the anti-oxidation ability of materials, and the molybdenum element effectively inhibits high-temperature creep deformation. This table is only for basic reference. The actual allowable working pressure cannot be directly copied from the table. You need to refer to the ASME B16 .34 temperature-pressure rating table according to the actual operating temperature and pressure grade. Do not use it beyond the temperature and pressure limits; otherwise, safety hazards will be hidden.
Analysis of Core Performance Differences
Based on the difference in composition, we can further sort out the four major performance differences that affect engineering practical applications.
- High temperature creep resistance: WC9 contains higher chromium-molybdenum alloy elements, which can stabilize the carbide structure in the metal matrix, effectively slow down creep deformation under long-term high temperature and high pressure loads, and reduce the risk of permanent wall thickness deformation of the valve body. For the main steam pipeline of supercritical power plants, creep resistance is one of the most important evaluation indices of high-temperature alloy steel valves.
- Antioxidant scale performance: WC9 with higher chromium content, will form a dense chromium oxide protective film on the inner wall of the valve flow channel, slow down the oxidation of high-temperature steam and scale on the inner wall, reduce the risk of scale debris scratching the sealing surface, and be suitable for refineries and supercritical power plant equipment.
- Hydrogen medium adaptability: WC9 has better hydrogen embrittlement resistance. Compared with WC6 valves, it is less likely to produce internal hydrogen-induced cracks in high-pressure hydrogen-rich medium environments in hydrocracking and hydrocracking units.
- Manufacturing and cost factors: The cost of WC9 alloy raw materials is higher; At the same time, the heat treatment tempering temperature requirement is higher, the cooling rate control is stricter, the production cycle and processing difficulty increase simultaneously, and the overall product cost is higher than WC6 valves.
Standard Application Conditions for Sedelon WC6 and WC9 Alloy Valves
Full Applicability Range of WC6 Valves
As a cost-effective high-temperature alloy steel valve, the Sedelon WC6 valve is widely used in medium- and high-temperature process pipelines with continuous operating temperatures below 538 ℃, covering the power and petrochemical industries.
- Power plant scenario: Subcritical power plant auxiliary steam pipeline, oxygen removal device outlet isolation circuit, boiler water bypass and cut-off valve, secondary reheat auxiliary pipeline;
- Refinery scenario: Steam pipeline of vacuum distillation tower, cut-off valve of heat exchanger inlet and outlet, process pipeline of medium-temperature light hydrocarbon;
- Compatible media: overheated steam below 538°C, high-temperature heat transfer oil, high-temperature process fluids without hydrogen;
- Recommended valve type: WC6 gate valve, WC6 stop valve, WC6 check valve; Seam weld / RTJ flange connection, Class150-Class1500 pressure rating.
- WC6 is not suitable for long-term continuous operation at temperatures above 538℉;It is also not recommended to load heavy hydrogen equipment in refineries. Even if the short-term temperature falls within the WC6 range, the above conditions must be upgraded to use WC9 alloy steel valves.
Specific Stringent High-Temperature Conditions for WC9 Alloy Steel
The WC9 alloy steel valve of Sedelon WC9 is used as the core station alloy valve of the supercritical unit and the hydrogenation unit of the refinery for harsh conditions that exceed the temperature limit of WC6 or hazardous media containing hydrogen.
- Power plant scenario: Main steam pipeline of supercritical boiler, isolation valve of first reheater, cut-off circuit of high-pressure steam turbine inlet, isolation of high-temperature steam main pipe;
- Refinery Scene: Hydrogenation Cracking, Inlet and Outlet of Hydrogenation Reactor, High-Temperature Reforming Pipeline, High-Temperature Heavy Oil and Slag Oil Loop;
- Compatible media: 538-593°C overheated steam, high-temperature heavy hydrocarbons, high-pressure hydrogen-rich process media;
- Recommended valve type: Pressure self-tightening gate valve, high-temperature stop valve, high-pressure check valve, RTJ flange / welded end, Class 600-Class 2500 high pressure rating.
- If the operating condition has frequent temperature fluctuations, and the short-term peak temperature exceeds 538°C, engineering practice still recommends using WC9 alloy steel to avoid the cumulative damage caused by alternating temperature cycles.
Complete Set of Standard Parameters for Sedelon WC6/WC9 Alloy Valves
Unified Design Implementation Standards
All WC6, WC9 alloy steel valves of Sedelon strictly implement the entire set of international standard systems, covering casting material, structural design, end size, welding, and finished product acceptance, ensuring product interchangeability and meeting global EPC project bidding requirements:
– Casting material standard: ASTM A217 WC 6 / WC 9;
– Design structure: API 600, ASME B16. 34;
– End dimensions: ASME B16. 5 flanges, ASME B16 . 25 welds;
– Test specification: API 598;
‑ Welding evaluation of pressure-bearing welds: ASME Volume IX.
Complete Nominal Diameter and Pressure Coverage
The WC6 and WC9 alloy steel valves of Sedelon have rich diameter and pressure grade coverage, including the mainstream specifications of power plants and refineries. When selecting the connection form, high-temperature and high-pressure alloy valves generally prefer to use welding or RTJ flanges, and try to avoid ordinary RF flanges to reduce the risk of leakage under temperature cycling conditions.
| Parameter Item | WC6 Valve | WC9 Alloy Steel Valve |
| Pressure Rating | Class 150 ~ Class 1500 | Class 150 ~ Class 2500 |
| Nominal Bore NPS | NPS 2″–NPS 24″ | NPS 2″–NPS 24″ |
| Connection Type | RF / RTJ Flange, BW Butt-Weld | Preferential RTJ Flange, BW Butt-Weld (High Pressure) |
| Actuation Type | Handwheel, Gear, Electric / Pneumatic Actuator | Handwheel, Gear, Electric / Pneumatic Actuator |
Special projects can be customized with non-standard dimensions; for Class 900 and above high-pressure grade alloy valves, Sedelon adopts a pressure self-tight valve cover structure, replacing the bolt valve cover, to improve the reliability of sealing under long-term temperature cycle load. Customers can also be equipped with special high-temperature actuators if needed.
Standard Internal Component Matching
The material of the internal part must match the alloy material of the valve body; otherwise, the mismatch of the coefficient of thermal expansion under temperature cycling will cause the valve to be stuck, the seal to fail, and the parts to wear out quickly.
‑ WC6 series: A182-F11 forged alloy valve stem, Stellite 6 hard alloy cladding on the sealing surface;The gate valve adopts an elastic wedge gate plate.
– WC9 series: A182-F22 forged alloy valve stem, Stellite 12 cladding to enhance high-temperature wear resistance; The high-pressure model is equipped with a pressure self-tight valve cover.
‑ All internal components are made of materials that meet ASME B16,34 thermal expansion matching to avoid failure caused by mismatched thermal expansion.
Sedelon Alloy Valve Full-Process Quality Control System
The chromium-molybdenum alloy steel valves of power plants and refineries are key pressure-bearing equipment. The tiny defects inside the castings and welds will quickly expand under the high-temperature and high-pressure cyclic load, causing serious safety accidents. Sedelon implements strict full-chain quality control for WC6, WC9 high-temperature alloy steel valves, covering raw material inspection at the factory, alloy special heat treatment production line, certified welding management, and multiple rounds of finished product inspection, meeting the acceptance requirements of power plants and refineries.
Alloy Raw Material Testing Before Production
Each batch of WC6 / WC9 castings is tested for PMI spectral composition to verify the content of chromium-molybdenum alloy elements and eliminate the risk of material mixing. The report of the chemical composition of castings and the report of mechanical tests are fully archived, so that the whole process can be traced. Unqualified raw materials are directly rejected and do not enter the machining process, avoiding the flow of wrong materials into subsequent production stages from the source.
Alloy-Specific Standardized Heat Treatment Production Line
Heat treatment is the core process that determines the final high-temperature performance of WC6 and WC9 cast alloy valves. According to the ASTM A219 standard, WC6 and WC9 require different tempering temperatures, and Sedelon has configured an independent alloy steel heat treatment furnace with precise temperature monitoring and recording functions.WC6 minimum tempering 595℉, WC9 minimum tempering 675℉.Stabilize the metal grain structure by normalizing and tempering, ensure high-temperature creep resistance, and avoid delayed cracks after field operation. The heat treatment curve can be provided together with the project data when the customer needs it.
WPS/PQR Certified Standardized Welding
All the welds on the pressure-bearing body of the valve, the welds on the connecting pipe, and the spot welds are executed according to the ASME Volume 9 effective WPS/PQR process evaluation, and only WPQ welders with qualifications can perform welding on alloy steel. Strictly enforce the preheating and post-weld heat treatment parameters to avoid the cold crack defect of chromium-molybdenum alloy steel. Each welding process record is archived and available for project review.
Multiple Rounds of Non-Destructive Testing + Hydrostatic Testing of Finished Products
Machining and assembly are completed, and each alloy valve is subjected to multi-dimensional inspection to detect surface and internal defects in sequence.
- Visual inspection + casting PT penetrant inspection to detect surface micro-cracks;
- RT X-ray non-destructive inspection for all critical pressure-bearing welds;
- 1.5 times the rated pressure shell water pressure strength test;
- Perform valve seat leakage test according to API 598 standard.
Sedelon can provide a complete ITP inspection plan, PMI report, complete WPS/PQR welding documents, and factory test certificate for EPC bidding and on-site inspection.
FAQs
Q1：Sedelon WC6 Q1 What is the maximum long-term operating temperature of the valve?
A1：Maximum continuous temperature of 538℃, suitable for high-temperature steam pipelines in conventional power plants and oil refineries.
Q2：Under what operating conditions must WC9 alloy steel valves be selected instead of WC6?
A2：When the medium temperature exceeds 540℃, or when the medium contains corrosive media such as hydrogen or ammonia (hydrogenation reactors, supercritical main steam pipelines).
Q3: Which industry standards do Sedelon WC6 and WC9 alloy valves comply with?
A3: ASTM A217 material standard, API 600, ASME B16.34, and a complete set of WPS/PQR welding qualification documents.
Q4: What pressure ratings and diameters do Sedelon WC9 alloy steel valves cover?
A4: Class 150 to Class 2500, 2-inch to 24-inch full diameter, supporting high-pressure RT flanges and butt-welded construction.
Q5: Can Sedelon provide PMI material reports and complete welding documentation for alloy valves?
A5: Yes, it is acceptable; we can provide PMI test reports, WPS/PQR, and factory inspection ITP forms for engineering bidding and project archiving.
Conclusion
Proper selection of WC6 valve and WC9 alloy valve is critical for pipeline safety. WC6 delivers good cost‑effectiveness under 538 °C, while WC9 alloy valve suits higher‑temperature supercritical steam and hydrogen‑rich media. As a professional high-temperature alloy steel valve producer, Sedelon complies with ASTM A218, API and ASME standards. Verified tests and full documentation make its power station alloy valve qualified for thermal‑power and refinery projects for global EPC contractors and distributors.
