ASTM A691 Chrome Moly EFW Steel Pipe: Complete Grade Guide for High-Temperature High-Pressure Service

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Womic Steel manufactures ASTM A691 electric-fusion-welded (EFW) steel pipe in the full range of chrome-moly grades for high-pressure service at elevated temperatures. This page is the entry point for the A691 product family—it explains what the specification covers, how the grades progress from 1Cr to 9Cr, what Class 22 means across the family, and links to the individual grade pages for detailed specifications, project cases, and ordering information.

Key search terms covered on this page: ASTM A691 chrome moly EFW pipe, A691 EFW steel pipe, chrome moly welded pipe, high temperature EFW pipe, A691 grade chart, A691 Class 22, A387 plate welded pipe, 1Cr 1.25Cr 2.25Cr 5Cr 9Cr EFW pipe.

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What ASTM A691 Covers

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 specification nominally covers pipe 16 inches (400 mm) outside diameter and larger with wall thicknesses up to 3 inches (75 mm) . The EFW process uses filler metal and allows the use of plate that has been rolled and welded into cylindrical shape, which makes large-diameter and heavy-wall pipe possible where seamless pipe is unavailable or uneconomical.

The A691 family is built around chromium-molybdenum plate grades from ASTM A387. Each A691 grade corresponds to a specific A387 plate grade, and the finished pipe’s chemistry and mechanical properties follow that plate specification.

A691 Grade Progression: 1Cr to 9Cr

The grades form a progression of increasing chromium and molybdenum content, each suited to progressively more aggressive high-temperature environments. The table below summarizes the family and links to the detailed page for each grade.

Grade	Base Plate	Cr Content	Mo Content	Primary Driver for Selection	Detailed Page
1Cr	A387 Gr.12	~1.00%	~0.50%	Moderate elevated temperature, lower alloy cost	ASTM A691 1Cr CL22
1.25Cr	A387 Gr.11	1.00–1.50%	0.45–0.65%	General high-temp steam and process lines	ASTM A691 1.25Cr CL22
2.25Cr	A387 Gr.22	2.00–2.50%	0.90–1.10%	Hydrogen service, power plant steam	ASTM A691 2.25Cr CL22
5Cr	A387 Gr.5	4.00–6.00%	0.45–0.65%	Refinery sulfidation resistance	ASTM A691 5Cr CL22
9Cr	A387 Gr.9	8.00–10.00%	0.90–1.10%	Severe oxidation, advanced power cycles	ASTM A691 9Cr CL22

The progression is not arbitrary. Each step up in chromium content buys additional oxidation resistance, elevated-temperature strength, and resistance to specific corrosion mechanisms such as sulfidation and hydrogen attack. The trade-off is higher cost, more demanding welding and heat treatment, and reduced availability of plate. Selecting the right grade means matching the alloy content to the actual service environment, not simply choosing the highest grade available.

Class 22 in the A691 Family

Class 22 is one of the most commonly specified class designations across the A691 grades. It requires stress relieving after welding, full radiographic examination of the longitudinal seam, and hydrostatic testing . For the higher chrome-moly grades—especially 5Cr and 9Cr—the stress relief step is metallurgically critical, not just a specification formality, because these steels form hard microstructures in the weld and heat-affected zone that must be tempered to restore toughness.

Class	Heat Treatment	Radiography	Pressure Test	Typical Use
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	Critical high-temp piping

For critical power plant piping, Class 42 is often specified in EPC documents because it combines full RT with normalized-and-tempered heat treatment. Class 22 is appropriate where stress relieving alone satisfies the design code and the operating conditions do not require normalized plate properties in the finished pipe.

Size Range Across the A691 Family

Womic produces A691 chrome-moly pipe in all the grades listed above using LSAW with single or double straight seam configuration.

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
Grades	1Cr, 1.25Cr, 2.25Cr, 5Cr, 9Cr

Single Straight Seam vs Double Straight Seam

Single straight seam 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 and PWHT on a single seam.

Double straight seam covers OD from about 1,200 mm to 2,540 mm with wall thickness up to 75 mm or more. Two plates are rolled into half-cylinders and each is welded longitudinally. The trade-off is two weld seams to inspect and heat treat, but it enables large-diameter alloy pipe that single seam cannot produce.

Applications Across the A691 Family

The grade progression maps directly onto application temperature and corrosion severity.

Power plant steam piping—1Cr and 1.25Cr for reheat cold-end and moderate-temperature steam lines; 2.25Cr for main steam and hot reheat where temperatures exceed the 1.25Cr range; 9Cr for supercritical and ultra-supercritical service

Refinery hydroprocessing—2.25Cr for hydrocracker and hydrotreater piping where hydrogen attack resistance is required

Refinery reforming and visbreaking—5Cr for sulfidation resistance at 400–500°C

Large-diameter alloy headers—all grades where seamless pipe above NPS 24 is impractical

Petrochemical high-pressure piping—grade selected by operating temperature and stream corrosivity.

Project Cases Across the A691 Family

Power Plant Reheat Steam Piping (China, 2011)

A Chinese power plant project used ASTM A691 1CR CL22 and 2.25Cr CL22 LSAW pipe for reheat steam cold-end piping, in OD ranges of 610–1219 mm and wall thicknesses of 9.52–42 mm. This project was documented at the 14th China (Northern) Steel Pipe and Pipeline Technology Conference and confirms the acceptance of A691 CL22 LSAW pipe in Chinese power plant steam piping where full RT and PWHT are mandatory.

High-Pressure Bypass Piping Replacement (China, 2024)

A 2024 maintenance project at a 350 MW supercritical thermal power plant in China specified A691 Gr.2-1/4Cr CL22 pipe for high-pressure bypass downstream piping replacement. The scope included pipe installation with PWHT and NDT, confirming that A691 CL22 grades remain the standard choice for high-temperature power plant maintenance where seamless pipe is unavailable or uneconomical.

Refinery Hydroprocessing Piping (Middle East)

A refinery project in the Middle East specified A691 2.25Cr CL22 EFW pipe for hydroprocessing unit piping in OD 610 mm and 762 mm, wall thickness 25 mm and 30 mm, with full RT and PWHT per Class 22. The 2.25Cr grade was selected for resistance to hydrogen attack at the operating temperature and hydrogen partial pressure of the hydrotreater.

Quality Documentation Across the Family

Each shipment of A691 chrome-moly 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)

Frequently Asked Questions

Q: Which A691 grade should I choose for my application?

The grade is determined by the operating temperature, the process stream chemistry, and the design code’s allowable stress tables. As a general guide: 1Cr and 1.25Cr for moderate elevated-temperature steam and process lines; 2.25Cr for higher-temperature steam and hydrogen service; 5Cr for refinery sulfidation service; 9Cr for the highest temperature power plant service within the chrome-moly range. The detailed grade pages linked above provide the specific chemistry, temperature limits, and application notes for each grade.

Q: What is the difference between A691 and A671?

Both specifications cover electric-fusion-welded pipe with filler metal, fabricated from pressure-vessel-quality plate. The difference is the base plate family. A671 uses carbon steel plate grades (CA, CB, CC series) for atmospheric and lower-temperature service. A691 uses chromium-molybdenum alloy plate grades (1Cr through 9Cr) for high-pressure service at elevated temperatures. The class system for heat treatment, radiography, and testing is similar across both specifications.

Q: What does Class 22 mean across the A691 grades?

Class 22 means stress relieving after welding, full radiographic examination of the longitudinal seam, and hydrostatic testing. For the higher chrome-moly grades such as 5Cr and 9Cr, the stress relief step is metallurgically critical because these steels form hard microstructures during welding that must be tempered to restore toughness. The PWHT chart should be reviewed as part of the documentation package.

Q: Can you supply mixed grades in one order?

Yes. Womic produces all the A691 grades listed on this page. If a project requires multiple grades for different services—for example, 1.25Cr for reheat lines and 2.25Cr for main steam—the grades can be produced and documented separately within the same order, with each grade receiving its own mill certificate, RT report, and PWHT chart.

Q: What is the lead time for A691 chrome-moly pipe?

Lead time depends on the grade, size, and quantity. Standard lead time for Class 22 pipe in common sizes is 30–45 days. Higher chrome-moly grades such as 5Cr and 9Cr may require longer lead times due to plate availability and the more demanding PWHT requirements. Contact Womic Steel with the specific grade, size, and quantity for a confirmed lead time.

Contact Womic Steel for ASTM A691 chrome-moly EFW pipe quotations. Provide the grade, outside diameter, wall thickness, quantity, length, end finish, PWHT requirements, 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

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