ASTM A691 1-1/4CR Pipe

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ASTM A691 1-1/4Cr EFW Pipe

Large-Diameter 1.25Cr-0.5Mo Electric-Fusion-Welded Pipe for High-Pressure and High-Temperature Service

 

Xi'an Dongmeng Group Co., Ltd. supplies ASTM A691 1-1/4Cr electric-fusion-welded alloy steel pipe for refinery, petrochemical, power generation and high-temperature process piping projects.

ASTM A691 1-1/4Cr is a chromium-molybdenum EFW pipe manufactured from pressure-vessel-quality ASTM A387/A387M Grade 11 plate. The nominal 1.25% chromium and 0.5% molybdenum alloy system provides better elevated-temperature strength and oxidation resistance than conventional carbon steel.

For large-diameter piping where seamless ASTM A335 P11 may become commercially or dimensionally restrictive, A691 1-1/4Cr provides an engineered welded-pipe option. However, A691 and A335 P11 are different product specifications and should not be treated as automatically interchangeable without engineering and code review.

The designation contains two different pieces of purchasing information.

ASTM A691 defines an electric-fusion-welded carbon or alloy steel pipe manufactured from pressure-vessel-quality plate for high-pressure service at elevated temperature.

1-1/4Cr identifies the chromium-molybdenum material family. For this grade, the source plate corresponds to ASTM A387/A387M Grade 11, commonly described as a nominal 1.25Cr-0.5Mo alloy.

This distinction becomes important when preparing a purchase order because an A691 pipe normally requires both a grade and a class.

For example:

ASTM A691 1-1/4Cr Class 22

Here, 1-1/4Cr is the material grade, while Class 22 defines the pipe manufacturing heat-treatment and inspection combination.

A frequent purchasing mistake is confusing A691 material grade with A691 pipe class.

The grade identifies the pressure-vessel plate material used to manufacture the pipe.

The class identifies the manufacturing treatment and verification requirements applied to the finished pipe.

A practical way to understand the A691 class system is shown below.

The second digit indicates the inspection/testing combination.

Therefore, ASTM A691 1-1/4Cr Class 22 means:

1-1/4Cr material + stress-relieved pipe + radiographic examination + pressure testing.

This is different from A691 2-1/4Cr, which is another material grade based on a higher chromium-molybdenum alloy system.

A691 1-1/4Cr is manufactured from ASTM A387 Grade 11 Cr-Mo pressure-vessel-quality plate.

Typical heat-analysis limits are:

The chromium addition improves resistance to high-temperature oxidation, while molybdenum contributes to elevated-temperature strength and creep resistance.

This alloy should not, however, be marketed as a general-purpose corrosion-resistant material in the same way as stainless steel. Process-fluid compatibility must be evaluated separately.

Mechanical requirements depend partly on the strength class of the ASTM A387 Grade 11 plate specified for production.

Important: ASTM A387 plate Class 1/Class 2 should not be confused with ASTM A691 pipe Class 11, 22, 32, 42, etc.

For project procurement, the material strength level, A691 pipe class and applicable design code should therefore be identified separately in the purchase specification.

Class 22 is one of the most frequently requested configurations for critical large-diameter Cr-Mo EFW piping.

Under the A691 classification system, Class 22 specifies:

Stress relief after pipe manufacture

Radiographic examination of the weld

Pressure testing

This combination provides considerably more verification than an A691 class that does not require radiography or pressure testing.

For refinery, petrochemical and power-generation projects, the required class should always be specified by the purchaser, EPC contractor or piping engineer rather than selected only on price.

Production normally begins with traceable ASTM A387 Grade 11 pressure-vessel-quality plate.

The plate is identified by heat number and verified against the purchase specification before forming.

The plate is then formed into cylindrical pipe sections using suitable large-diameter forming equipment.

The longitudinal joint is electric-fusion welded with filler metal. Submerged arc welding may be used as the production welding process where suitable for the manufacturing procedure.

After welding, the pipe receives the heat treatment required by its ordered A691 class.

The weld and pipe are then inspected and tested according to the ordered class and any supplementary project requirements.

Final dimensional inspection, marking, documentation review and packing are completed before shipment.

ASTM A691 does not impose the same radiographic requirement on every class.

Radiographic examination is determined by the specified A691 pipe class.

For example, Classes ending in 1 or 2 include radiographic examination, while Classes ending in 0 or 3 do not include radiography as part of the basic class designation.

For Class 22 pipe, radiographic examination is required.

Additional inspection such as ultrasonic examination, magnetic particle examination, liquid penetrant examination, hardness testing or expanded NDE scope can be arranged when required by the purchase specification, project code or inspection and test plan.

Pressure testing is also controlled by the ordered A691 class.

Classes ending in 2 or 3 include the specified pressure test, while classes ending in 0 or 1 do not include it as part of the class designation.

This is another reason an RFQ stating only "ASTM A691 1-1/4Cr" is incomplete for many engineered projects.

A preferred purchasing description would be:

ASTM A691/A691M 1-1/4Cr Class 22, OD × WT × Length, applicable standard edition, required documentation and supplementary inspection requirements.

ASTM A691 1-1/4Cr and ASTM A335 P11 belong to a similar Cr-Mo chemistry family, but they are different piping products.

A691 1-1/4Cr should therefore not simply be described as an "equivalent replacement" for A335 P11.

Material substitution should be approved by the responsible piping engineer after checking the applicable ASME piping code, design pressure, design temperature, allowable stress, joint quality factor, cyclic service requirements and project specification.

ASTM A691 1-1/4Cr pipe is primarily considered for large-diameter high-temperature process systems where Cr-Mo metallurgy and welded construction are appropriate.

Typical project areas include refinery process piping, petrochemical plants, power-generation systems, high-temperature steam service, hot hydrocarbon process lines, large-diameter headers and selected high-pressure process applications.

Final suitability depends on operating temperature, pressure, transported medium, corrosion mechanism, piping code and engineering design.

For 1.25Cr-0.5Mo piping systems, commonly specified matching material families include:

These are corresponding Cr-Mo material families, but final material selection, class, heat treatment and pressure-temperature rating must follow the applicable project design specification.

For high-temperature alloy piping, the default supply condition is commonly bare, cleaned or provided with temporary protective coating suitable for storage and transportation.

Shop primer, FBE, 3PE or other external coating systems may be supplied when specifically required.

However, coating suitability must be confirmed against the pipeline's actual operating temperature and service environment. Conventional organic coating systems should not automatically be specified for elevated-temperature service.

Dongmeng Group can supply project documentation according to the purchase specification.

Typical documentation includes material heat identification, chemical analysis, mechanical test results, heat-treatment records where applicable, dimensional inspection reports, weld examination records, pressure-test records when required by class, and an EN 10204 3.1 Material Test Certificate.

EN 10204 3.2 documentation or third-party inspection by organizations such as SGS, TÜV, BV or other purchaser-approved inspection agencies can be arranged when specified before production.

Heat-number traceability can be maintained from source plate through finished pipe and shipment documentation.

For an accurate technical and commercial quotation, the RFQ should state the complete material designation rather than simply "A691 pipe."

Providing these details at RFQ stage reduces technical clarification cycles and helps avoid incorrect quotations based on the wrong class or inspection level.

Xi'an Dongmeng Group Co., Ltd. supplies alloy steel piping for international industrial projects with support covering material selection, technical document review, dimensional customization, inspection coordination and export delivery.

For ASTM A691 project orders, our focus is not only the pipe dimensions but also the complete purchasing specification: base plate grade, A691 class, heat treatment, weld examination, pressure testing, documentation and traceability.

OEM cutting, project-specific lengths, bevel preparation, marking, coating and export packing can be arranged according to the purchase order.

Third-party inspection and additional testing can also be coordinated when specified before production.

What is ASTM A691 1-1/4Cr pipe?

ASTM A691 1-1/4Cr is an electric-fusion-welded chromium-molybdenum alloy steel pipe manufactured from pressure-vessel-quality ASTM A387 Grade 11 plate. It is intended primarily for high-pressure service at elevated temperature.

Is ASTM A691 1-1/4Cr the same as A335 P11?

No. They have related nominal Cr-Mo chemistry, but A691 1-1/4Cr is an EFW welded pipe manufactured from plate, while A335 P11 is a seamless alloy steel pipe specification. Interchangeability requires engineering and code approval.

What does A691 Class 22 mean?

Class 22 specifies stress relief of the pipe, radiographic examination of the weld and pressure testing.

Is A691 Class 22 the same as Grade 22?

No. This is an important distinction. "Class 22" is a heat-treatment and inspection designation. "2-1/4Cr," corresponding to the higher-alloy Grade 22 plate family, is a different material grade.

Does every ASTM A691 pipe require radiographic examination?

No. Radiography depends on the ordered class. Classes ending in 1 or 2 include radiographic examination under the A691 class system.

Does every A691 pipe require pressure testing?

No. Pressure testing depends on the ordered class. Classes ending in 2 or 3 include the pressure test within the class designation.

Does ASTM A691 require all pipe to be normalized and tempered?

No. The required heat treatment depends on the class. The standard includes classes with no pipe heat treatment, stress relief, normalizing, normalizing and tempering, or quenching and tempering.

What sizes does ASTM A691 cover?

The standard nominally covers pipe 16 in. [400 mm] OD and larger with wall thickness up to 3 in. [75 mm]. Other dimensions may be supplied when they comply with the other applicable requirements of the specification.

Can A691 1-1/4Cr be supplied with 3PE or FBE coating?

Coating can be supplied when required, but the coating system must be selected according to actual service and operating temperature. 3PE or conventional FBE should not automatically be specified for high-temperature operating conditions.

What documents should I request?

For industrial procurement, an EN 10204 3.1 MTC, heat-number traceability, chemistry and mechanical test results should normally be requested. Depending on the A691 class and project requirements, heat-treatment, RT and pressure-test records may also be required.

Can third-party inspection be arranged?

Yes. Third-party inspection can be coordinated according to the approved inspection and test plan when specified before production.

What information should I send for a quotation?

Please provide ASTM standard and edition, 1-1/4Cr grade, required A691 class, OD, wall thickness, length, quantity, plate strength requirement where specified, end preparation, testing requirements, documentation level, applicable piping code and delivery destination.

For ASTM A691 1-1/4Cr Class 22 pipe quotations, please send your material specification, OD × wall thickness, length, quantity, required class and inspection requirements.

Xi'an Dongmeng Group Co., Ltd.

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Email: office@dongmjd.com
Office: Room 4107, Runfeng Building, Sanqiao New Street, Weiyang District, Xi'an City, Shaanxi Province

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