What ASTM A691 1.25Cr CL22 Means
ASTM A691 covers carbon and alloy steel pipe, electric-fusion-welded with filler metal added, fabricated from pressure-vessel-quality plate, suitable for high-pressure service at high temperatures . The designation breaks into three parts.
Grade 1.25Cr identifies the base plate. This grade corresponds to ASTM A387 Gr.11, a chromium-molybdenum alloy steel plate designed for elevated-temperature service. The chromium content provides oxidation resistance and elevated-temperature strength, while molybdenum contributes creep resistance and hardenability. The pipe’s chemistry and mechanical properties follow the A387 Gr.11 plate specification.
Class 22 defines heat treatment and testing. Class 22 requires the pipe to be stress relieved after welding, the longitudinal weld seam to be radiographically examined, and the finished pipe to undergo hydrostatic testing . This class sits in the middle of the A691 class system, providing PWHT and full RT without the normalization or quenching-and-tempering required by higher classes.
EFW indicates the manufacturing method: alloy steel plate is formed into cylindrical shape, and the longitudinal seam is welded using submerged arc welding (SAW) with filler metal added . This differs from ERW pipe, which uses no filler metal.
Chemical and Mechanical Properties
Because 1.25Cr is tied to A387 Gr.11 plate, the finished pipe’s chemistry and strength follow that plate standard.
| Property | Typical Value |
| Carbon | 0.05–0.17% |
| Manganese | 0.40–0.65% |
| Phosphorus (max) | 0.025% |
| Sulfur (max) | 0.025% |
| Silicon | 0.50–0.80% |
| Chromium | 1.00–1.50% |
| Molybdenum | 0.45–0.65% |
| Yield Strength (min) | 310 MPa |
| Tensile Strength | 515–690 MPa |
| Elongation (min) | 18% |
| Max Operating Temperature | 565–593°C |
The chemistry and mechanical values above are representative for A387 Gr.11 plate and finished A691 1.25Cr pipe . Actual test results on the mill certificate reflect the specific heat and plate used. Class 22 stress relieving does not alter the base chemistry.
Grade Comparison: 1.25Cr vs 2.25Cr vs 1Cr
Buyers searching 1.25Cr often compare it against the neighboring chrome-moly grades. The difference is chromium and molybdenum content, which drives elevated-temperature strength and creep resistance.
| Grade | Base Plate | Cr Content | Mo Content | Typical Use |
| 1Cr | A387 Gr.12 | ~1% | ~0.5% | Moderate elevated temperature |
| 1.25Cr | A387 Gr.11 | 1.00–1.50% | 0.45–0.65% | General high-temp steam and process lines |
| 2.25Cr | A387 Gr.22 | ~2.25% | ~1.0% | Higher temperature, hydrogen service |
1.25Cr is often selected for steam piping and process lines where the metal temperature falls within its creep range but does not require the higher chromium content of 2.25Cr for oxidation resistance or hydrogen attack resistance.
Class 22 vs Other A691 Classes
Class 22 is frequently specified for high-temperature piping, but buyers often ask how it compares to Class 12 (RT without PWHT) and Class 32 (normalized plus PWHT).
| Class | Heat Treatment | Radiography | Hydrotest | Typical Specification |
| 12 | None | Full RT | Yes | As-welded, moderate service |
| 22 | Stress Relieved | Full RT | Yes | High-temp service with PWHT |
| 32 | Normalized | Full RT | Yes | Higher toughness demand |
| 42 | Normalized + Tempered | Full RT | Yes | Severe service, critical high-temp |
For critical high-temperature piping, Class 42 is often the standard requirement in EPC specifications . Class 22 is appropriate where stress relieving is sufficient and normalized plate properties are not required by the design code.
Size Range and Manufacturing Options
Womic produces A691 1.25Cr CL22 pipe using LSAW with either single straight seam or double straight seam configuration. ASTM A691 nominally covers pipe 16 inches (400 mm) outside diameter and larger with wall thicknesses up to 3 inches (75 mm) .
| Parameter | Range |
| Outside Diameter | 16″ to 100″ (400 mm to 2,540 mm) |
| Wall Thickness | 6 mm to 75 mm (heavier on request) |
| Length | 6 m, 12 m standard; up to 18 m or 24 m on request |
| Manufacturing Method | EFW / LSAW with filler metal |
| Seam Type | Single straight seam or double straight seam |
Single Straight Seam vs Double Straight Seam
Single straight seam is used when one plate can be rolled into a full cylinder. At Womic this covers OD up to about 1,422 mm with wall thickness up to 50.8 mm on the JCOE line. One longitudinal weld concentrates inspection on a single seam.
Double straight seam is used when diameter or wall thickness exceeds what a single plate can form. Two plates are rolled into half-cylinders and each is welded longitudinally. This covers OD from about 1,200 mm to 2,540 mm with wall thickness up to 75 mm or more. The trade-off is two weld seams to inspect, but it enables large-diameter alloy pipe that single seam cannot produce.
Welding and Heat Treatment
The longitudinal seam is welded by submerged arc welding with filler metal selected to match the 1.25Cr base metal. After welding, the pipe is stress relieved per Class 22 requirements: heated uniformly to a temperature below the critical range, held for a time proportional to wall thickness, and cooled in a controlled manner. This relieves residual stresses from forming and welding and stabilizes the microstructure for elevated-temperature service.
For 1.25Cr pipe, post-weld heat treatment is not merely a specification formality. The chromium-molybdenum steel is susceptible to hardness and cracking in the heat-affected zone if cooled too rapidly after welding, so the stress relief serves both dimensional stability and metallurgical control.
What Class 22 Testing Involves
Stress Relieving: After welding, the pipe is heated to a temperature below the critical range and held to relieve residual stresses.
Radiographic Examination: The longitudinal weld seam is examined by X-ray or gamma ray to detect internal defects. Class 22 requires full RT of the longitudinal seam, not spot examination.
Hydrostatic Testing: Each pipe is filled with water and pressurized to a level determined by the specified wall thickness and diameter, held for a defined period, and inspected for leaks or permanent deformation.
Supplementary requirements in ASTM A691 can be invoked for impact testing, additional radiography, or hardness testing when the project demands more than the base Class 22 scope.
Applications for A691 1.25Cr CL22 Pipe
Power plant steam piping including superheater and reheater lines, main steam, and hot reheat piping where the metal temperature falls within the 1.25Cr creep range
Refinery high-temperature transfer lines carrying process fluids at elevated temperature where carbon steel is inadequate
Large-diameter alloy headers where seamless pipe above NPS 24 is impractical or unavailable
Petrochemical high-pressure piping in hydrocracking and hydrotreating units where chrome-moly pipe is specified for temperature and pressure resistance
Project Cases
India Power Station Maintenance Project (2022)
A power station maintenance project in India specified ASTM A691 1.25Cr CL22 EFW pipe, 508 mm OD × 25.4 mm WT × 12,000 mm, quantity 6 pieces . This case demonstrates the use of 1.25Cr CL22 pipe for power station maintenance and replacement work, where the pipe must match the existing high-temperature steam system’s material specification and be available in short lead times.
European Low-Temperature Pipeline Reference
While the specific grade in this project was CC60, the same A671/A691 Class 22 production route was used for a low-temperature pipeline in Germany (922 metric tons, OD 406.4–1,219.2 mm). For high-temperature service requiring 1.25Cr, the same EFW forming, welding, and stress-relieving equipment is used, with the plate specification changed to A387 Gr.11.
Quality Documentation
Each shipment of A691 1.25Cr CL22 pipe from Womic Steel includes:
● EN 10204 3.1 mill test certificate with chemical composition and mechanical test results traceable to the plate heat number
● Radiographic examination report for the weld seam
● Hydrostatic test record
● Post-weld heat treatment chart with temperature and holding time
● Dimensional inspection report
● Third-party inspection available upon request (SGS, BV, TÜV)
Packaging and Shipping
Pipes are supplied with beveled ends protected by plastic caps, or plain ends as specified. The pipe surface receives a protective coating suitable for transport and storage. Small and medium diameters are bundled with steel straps; large diameters and heavy wall pipe are shipped individually with wooden dunnage. Third-party pre-shipment inspection can be arranged.
Frequently Asked Questions
Q: What is the difference between 1.25Cr and 1Cr in ASTM A691?
1.25Cr uses A387 Gr.11 plate with 1.00–1.50% chromium, while 1Cr uses A387 Gr.12 plate with approximately 1% chromium. The 1.25Cr grade has slightly higher chromium and molybdenum content, which provides better elevated-temperature strength and creep resistance. For many steam piping applications, the two grades are close in performance; selection depends on the design code’s allowable stress tables at the operating temperature.
Q: What does Class 22 mean for A691 1.25Cr pipe?
Class 22 means the pipe is stress relieved after welding, the longitudinal weld seam receives full radiographic examination, and the finished pipe is hydrostatically tested. This class is common for high-temperature piping where PWHT is required to stabilize the weld and heat-affected zone, and where full RT is specified for weld integrity verification.
Q: Can you supply A691 1.25Cr with impact testing?
Yes. Charpy V-notch impact testing is a supplementary requirement under ASTM A691. Specify the test temperature, specimen orientation, and acceptance criteria in the purchase order. Impact testing for chrome-moly pipe is less common than for low-temperature carbon steel, but can be arranged when the project specification requires it.
Q: What is the maximum temperature for A691 1.25Cr?
The maximum operating temperature is typically cited as 565–593°C (1050–1100°F), depending on the specific design code and allowable stress basis . Above this range, oxidation and creep resistance become limiting, and higher chromium grades such as 2.25Cr or 9Cr are typically specified.
Q: Is A691 1.25Cr the same as A387 Gr.11?
Not exactly. A387 Gr.11 is a steel plate specification. A691 1.25Cr is a pipe specification that uses A387 Gr.11 plate as starting material, forms and welds it into pipe, applies the heat treatment required by the class, and performs the specified testing. The finished pipe has chemistry and strength consistent with A387 Gr.11, but the product form and testing regime are governed by A691.
Q: Should I choose single straight seam or double straight seam?
The mill selects the seam configuration based on the ordered size. Single straight seam covers OD up to about 1,422 mm and wall thickness up to 50.8 mm at Womic. Double straight seam covers larger diameters and heavier walls. If your project specification restricts the seam type, state this in the purchase order.
Contact Womic Steel for ASTM A691 1.25Cr CL22 EFW pipe quotations. Provide the outside diameter, wall thickness, quantity, length, end finish, and any supplementary testing requirements. We will confirm availability and lead time within one business day.
Website: www.womicsteel.com
E-mail: sales@womicsteel.com
Tel / WhatsApp / WeChat:
Victor: +86 15575100681
Jack: +86 18390957568
Related Products
-
ASTM A691 1.25Cr CL22 EFW Steel Pipe: Manufactu...
-
ASTM A691 1Cr CL22 EFW Steel Pipe: The Entry-Le...
-
ASTM A671 EFW Steel Pipe: Complete Grade Guide ...
-
ASTM A691 2.25Cr CL22 EFW Steel Pipe for High-T...
-
ASTM A671 CC70 CL22 EFW Steel Pipe: Manufacturi...
-
ASTM A691 5Cr CL22 EFW Steel Pipe for Refinery ...
-
ASTM A671 CC65 CL22 EFW Steel Pipe: Manufacturi...
-
ASTM A691 9Cr CL22 EFW Steel Pipe for Power Pla...
-
ASTM A671 CC60 CL22 EFW Steel Pipe: Manufacturi...