ASTM A335 P11 Pipe

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ASTM A335 P11 Seamless Pipe

1.25Cr-0.5Mo Chrome Moly Alloy Steel Pipe for Elevated-Temperature Pressure Service

Xi'an Dongmeng Group Co., Ltd. supplies ASTM A335 P11 / ASME SA335 P11 seamless chromium-molybdenum alloy steel pipe for power generation, boiler systems, refineries, petrochemical plants and industrial high-temperature pressure piping.

ASTM A335 P11 is a nominal 1.25Cr-0.5Mo ferritic alloy steel combining chromium and molybdenum to provide improved elevated-temperature strength and oxidation resistance compared with conventional carbon steel.

P11 is widely specified in steam and process piping, but it should not be selected simply because it is described as a "high-temperature pipe." Final material selection must consider the applicable design code, design temperature and pressure, allowable stress, process medium, corrosion mechanism, welding requirements and project metallurgy specification.

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ASTM A335 P11 is a seamless ferritic alloy-steel pipe manufactured for elevated-temperature service.

The designation has two important parts.

ASTM A335 defines the seamless alloy-steel pipe specification.

P11 identifies the 1.25Cr-0.5Mo material grade.

P11 contains approximately 1.00–1.50% chromium and 0.44–0.65% molybdenum. Chromium contributes to resistance against high-temperature oxidation, while molybdenum contributes to elevated-temperature strength and hardenability.

P11 is therefore frequently used where conventional carbon steel does not provide the required elevated-temperature material performance.

However, ASTM A335 is a material specification, not a complete piping design code.

The allowable pressure, temperature and service life of a P11 piping system must be determined according to the applicable engineering code and project design.

ASTM A335 P11 corresponds to UNS K11597.

These limits distinguish P11 from other ASTM A335 Cr-Mo grades such as P22, P5, P9 and P91.

The chromium-molybdenum combination is what gives P11 its characteristic elevated-temperature performance.

Chromium contributes to oxidation resistance and hardenability.

Molybdenum contributes to elevated-temperature strength and creep resistance.

This does not mean P11 should be marketed as a universally "corrosion-resistant" pipe.

Suitability for refinery, petrochemical or hydrogen-containing process environments must be evaluated against the actual corrosion and degradation mechanisms.

Typical minimum room-temperature tensile properties include:

The minimum tensile and yield requirements are 415 MPa and 205 MPa respectively.

A common supplier-page mistake is to write:

Elongation ≥30%

without qualification.

For P11, elongation requirements depend on the specimen orientation and dimensions.

For example, for applicable strip tests at approximately 8 mm wall thickness and above, the basic values are:

Longitudinal: 30%

Transverse: 20%

Calculated minimum elongation decreases for thinner test specimens according to ASTM requirements.

For purchasing documentation, it is therefore better to state:

Elongation: according to ASTM A335 specimen and wall-thickness requirements.

Heat treatment is one of the most important technical sections for a professional P11 page.

ASTM A335 P11 may be supplied in:

Full Annealed Condition

Isothermal Annealed Condition

or

Normalized and Tempered Condition

When P11 is supplied normalized and tempered, the minimum tempering temperature is:

1200°F [650°C]

The heat-treatment condition should be confirmed on the purchase order and material certificate.

Heat treatment affects:

Microstructure

Mechanical properties

Hardness

Weldability

Fabrication behavior

Elevated-temperature performance

Heat-affected-zone response during welding

For critical power-generation or refinery projects, buyers should review the heat-treatment condition rather than accepting a generic statement such as "heat treated according to ASTM."

ASTM A335 P11 is a seamless pipe specification.

A typical manufacturing route includes:

1. Steelmaking

Steel chemistry is controlled to meet the required P11 composition.

2. Billet Preparation

Qualified billets are identified by heat number and prepared for seamless processing.

3. Piercing

The solid billet is pierced to create a hollow shell without a longitudinal weld seam.

4. Hot Finishing or Cold Drawing

The hollow shell is processed to achieve the required outside diameter and wall thickness.

Cold drawing may be used where tighter dimensional or surface requirements are needed.

5. Heat Treatment

The pipe receives the specified finishing heat treatment.

6. Straightening and Finishing

Outside diameter, wall thickness, straightness, length and end condition are controlled.

7. Mechanical Testing and NDE

Required mechanical tests, hydrostatic testing and nondestructive examination are performed.

8. Final Inspection

Marking, dimensions, heat-number traceability and certification are verified before shipment.

This distinction should be very clear on a professional product page.

ASTM A335 P11 = Seamless Ferritic Alloy Steel Pipe

ASTM's current scope explicitly defines A335 as seamless pipe.

Therefore, products should not be advertised as:

A335 P11 ERW Pipe

or

A335 P11 Welded Pipe

For large-diameter welded 1.25Cr-0.5Mo pipe, an ASTM A691 1-1/4Cr EFW pipe may instead be evaluated according to project requirements.

These are different product specifications and are not automatically interchangeable.

Inspection should be presented as a purchasing requirement rather than a generic list of factory capabilities.

Under the current ASTM A335/A335M standard, each pipe is subject to hydrostatic testing and nondestructive examination according to the applicable requirements.

Typical quality verification includes:

Chemical Analysis

Verification of P11 chemistry and heat identity.

Tensile Testing

Verification of room-temperature mechanical properties.

Flattening or Bend Testing

Applied according to the applicable pipe dimensions and ASTM requirements.

Hydrostatic Testing

Used to verify pipe integrity under the specified test conditions.

Nondestructive Examination

Each pipe is examined by an applicable NDE method according to ASTM A335 requirements and the limitations of the referenced examination practice.

Depending on project requirements, additional testing may include:

Ultrasonic Examination

Eddy Current Examination

Flux Leakage Examination

PMI

Hardness Testing

Impact Testing

Surface Inspection

Dimensional Inspection

Third-Party Witness Inspection

The exact inspection scope should be stated in the purchase specification.

P11, P22, P5, P9 and P91 can appear visually identical in a warehouse or fabrication shop.

Their alloy chemistry is very different.

For projects handling several Cr-Mo grades, PMI can provide an additional safeguard against material mix-up.

PMI should be specified at RFQ stage if it is required by the project ITP or material-control procedure.

 ASTM A335/A335M currently covers seamless ferritic alloy-steel pipe intended for high-temperature service and requires hydrostatic testing and nondestructive examination

 Custom outside diameter, wall thickness, length, bevel angle, marking and packing can be supplied according to project drawings or purchase specifications.

ASTM A335 P11 seamless pipe is commonly used in industries where pipe systems must withstand high temperature, pressure and long-term service conditions.

Power Plant

Used for steam lines, boiler piping, superheater systems, reheater lines, headers and high-temperature pressure pipelines.

Petrochemical Plant

Used for process piping, high-temperature hydrocarbon service, refinery units, catalytic cracking systems and pressure piping networks.

Boiler and Pressure Equipment

Used in boiler construction, pressure vessel connection piping, heat recovery systems and high-temperature auxiliary systems.

Refinery and Oil & Gas

Used for hot process media, refinery piping, high-pressure systems and equipment connection lines.

Heat Exchanger System

Used for manifold piping, connecting pipes, high-temperature transfer lines and industrial heat exchange equipment.

These grades should not be presented as a simple "good → better → best" ranking.

P11 contains:

Cr 1.00–1.50%

Mo 0.44–0.65%

P22 contains:

Cr 1.90–2.60%

Mo 0.87–1.13%

Their minimum room-temperature tensile and yield strengths are the same under ASTM A335: 415 MPa tensile and 205 MPa yield.

Therefore, it is inaccurate to explain P22 simply as:

"P22 is stronger than P11."

The important differences involve chemistry, elevated-temperature behavior, oxidation resistance, hardenability, allowable stresses and service-specific metallurgy.

Final material selection should follow the applicable engineering code.

P11 may be specified where the engineering design requires a 1.25Cr-0.5Mo alloy and its corresponding code properties are adequate for the intended service.

That does not mean P11 should be selected simply because it costs less.

The selection should consider:

Design temperature

Design pressure

Allowable stress

Process environment

Corrosion mechanism

Required service life

Welding requirements

Existing plant metallurgy

Project material specification

P5 contains significantly more chromium than P11 but similar nominal molybdenum content.

Therefore P5 is not simply a "higher-temperature P11."

It belongs to a different alloy family and is frequently associated with refinery/process metallurgy where approximately 5% chromium is specified.

P91 is a creep-strength-enhanced ferritic steel containing approximately 9% chromium together with Mo, V, Nb and N additions.

It offers significantly different high-temperature mechanical behavior but also requires much tighter fabrication and heat-treatment control.

P91 should therefore not be presented as an automatic upgrade or replacement for P11.

These products have related Cr-Mo metallurgy but different manufacturing routes.

For large diameters where seamless P11 becomes commercially difficult, engineers may evaluate A691 1-1/4Cr.

However:

A691 1-1/4Cr is not automatically equivalent to or interchangeable with A335 P11.

The proposed substitution should be reviewed against the governing piping code and project specification.

Common corresponding material families include:

These materials belong to corresponding Cr-Mo families.

They should not, however, be treated as automatically interchangeable without checking component class, heat treatment, pressure rating and project requirements.

ASTM A335 P11 is suitable for fusion welding, but welding should be controlled by an approved WPS/PQR.

Important fabrication controls include:

Base-material verification

Low-hydrogen welding practice

Suitable Cr-Mo filler metal

Preheat

Interpass temperature

Heat input

Hydrogen control

PWHT

Hardness control

NDE

Repair-welding procedure

Suitable B2-family filler metals may be considered for P11 welding where permitted by the qualified welding procedure.

A product page should not give one universal preheat or PWHT temperature for every P11 joint.

Not as a universal ASTM A335 material requirement.

ASTM A335 specifies the supplied pipe material.

Post-weld heat treatment of a fabricated piping joint is controlled by factors such as:

Governing piping code

Material P-Number / Group

Wall thickness

Joint type

Service conditions

Welding procedure

Applicable exemptions

Project specification

Therefore, the purchaser and fabricator should follow the applicable construction code and approved WPS/PQR.

Avoid statements such as:

"All P11 welding must always receive PWHT at one fixed temperature."

That oversimplifies engineering requirements.

P11 is widely associated with elevated-temperature steam piping and boiler-related systems.

Potential applications include:

Steam headers

Steam distribution piping

Boiler connection piping

Power-generation process piping

HRSG-related piping

High-temperature auxiliary piping

However, ASTM A335 itself does not define one universal maximum operating temperature for P11.

Actual design temperature capability depends on code allowable stresses, pressure, wall thickness, design life and creep considerations.

No single temperature should be presented as the universal maximum temperature of all P11 pipe systems.

ASTM A335 is a material specification.

Final allowable design conditions depend on:

Applicable piping code

Allowable stress at temperature

Design pressure

Wall thickness

Design life

Creep considerations

Process environment

Welding condition

Thermal cycling

For high-temperature RFQs, the purchaser should provide both:

Design Temperature

and

Design Pressure

so that the project requirements can be technically reviewed.

ASTM A335 P11 may be used in refinery and petrochemical systems where 1.25Cr-0.5Mo metallurgy is specified.

Potential services include:

High-temperature hydrocarbon piping

Process-unit piping

Heater-related connecting lines

Hot process transfer lines

Pressure-equipment connections

However, P11 should not be marketed as generically resistant to every refinery corrosion mechanism.

Material suitability should be reviewed against the actual process chemistry and project corrosion/material selection criteria.

Cr-Mo steels are used in selected high-temperature hydrogen services, but the alloy designation alone does not establish suitability against high-temperature hydrogen attack.

Engineering review should consider:

Operating temperature

Hydrogen partial pressure

Material condition

Design life

Applicable industry guidance

Project metallurgy specification

The operating conditions should therefore be included in the RFQ for hydrogen-service projects.

Typical P11 supply conditions may include:

Bare

Light protective oil

Black surface

Temporary varnish

Project-specific external protection

FBE, 3PE or other coating systems may be supplied when specifically required and technically suitable.

The coating temperature rating must be checked against the actual operating environment.

An organic coating should not automatically be specified simply because the base pipe is designed for elevated-temperature service.

For international P11 projects, Dongmeng Group can provide an agreed documentation package including:

Heat number

Material Test Certificate

Chemical analysis

Mechanical test results

Heat-treatment condition

Hydrostatic test information

NDE documentation

Dimensional inspection

Product marking

Packing list

Certificate of origin where required

EN 10204 3.1 MTC can be supplied according to the agreed order.

EN 10204 3.2 certification or third-party inspection requirements should be stated before production so that inspection hold points and document requirements can be arranged correctly.

For complete pressure piping systems, ASTM A335 P11 pipe is commonly used together with matching fittings and flanges.

We can support buyers with pipe, fittings, flanges and related alloy steel materials according to project BOM requirements. 

ASTM A335 P11 pipe is suitable for fusion welding, but proper welding control is important for pressure piping systems. Preheating, interpass temperature control and post-weld heat treatment may be required depending on wall thickness, design code and project specification.

For welded piping systems, buyers should confirm:

Welding procedure specification

Preheat requirement

PWHT requirement

Filler metal selection

Hardness control after welding

NDT requirement after fabrication

Engineering code or project standard

We can supply pipes with heat treatment records, MTC, batch traceability and additional testing documents to support project fabrication and quality approval.

Xi'an Dongmeng Group Co., Ltd. follows a strict inspection process for ASTM A335 P11 seamless pipe before shipment.

Raw Material Inspection

Heat number verification

Chemical composition analysis

Material grade confirmation

Mill certificate review

Dimensional Inspection

Outside diameter check

Wall thickness check

Length inspection

Straightness inspection

End bevel and surface inspection

Mechanical and NDT Testing

Tensile test

Yield strength test

Elongation test

Hardness test

Hydrostatic test

Ultrasonic testing

Additional third-party inspection on request

ASTM A335 P11 pipes are packed for international shipment to reduce damage during handling, storage and sea transportation.

Standard Packing

Steel strip bundle packing

Plastic end caps

Waterproof wrapping

Anti-rust oil or varnish coating

Bundle labels

Shipping marks

Container loading support

Custom Packing

Wooden box or wooden frame for small sizes

Special marking according to project code

Color coding by grade

Barcode label

Heat number label

Customer logo or project tag on request

To help us quote accurately, please send the following information:

Standard: ASTM A335 / ASME SA335

Grade: P11

Pipe size: OD or NPS

Wall thickness: SCH or mm

Quantity: meters, pieces or tons

Length: 6m, 12m, SRL, DRL or cut length

Pipe ends: PE, BE or threaded

Testing requirement: hydrostatic test, UT, third-party inspection

Certificate requirement: MTC 3.1 or 3.2

Destination port

Required delivery time

Our sales and technical team will provide quotation, weight calculation, delivery schedule and document support for your project

 

 

 

Xi'an Dongmeng Group Co., Ltd. supports international Cr-Mo piping procurement with attention to material verification, dimensional control, traceability, testing and documentation.

For ASTM A335 P11 projects, we can support:

Material Verification
Heat number, chemistry and MTC review.

Standard & Heavy-Wall Sizes
Common schedules and project-specific heavy-wall requirements subject to mill capability.

Fixed-Length Processing
6 m, 12 m and project-specific cutting.

End Preparation
Plain end and beveled end according to purchase requirements.

Inspection Support
ASTM testing plus supplementary project inspection where specified.

PMI
Grade verification can be arranged for projects requiring additional alloy identification.

Third-Party Inspection
Purchaser-approved inspection agencies can be coordinated.

Export Packing
Pipe bundling, end protection, waterproof wrapping and seaworthy export packing.

Our objective is to provide the complete:

material + size + heat treatment + inspection + traceability + documentation

package required by the project.

1. What is ASTM A335 P11 pipe?

ASTM A335 P11 is a seamless ferritic alloy-steel pipe containing nominally 1.25% Cr and 0.5% Mo for elevated-temperature service.

2. Is ASTM A335 P11 seamless or welded?

ASTM A335 P11 is a seamless pipe specification.

For welded 1.25Cr-0.5Mo large-diameter pipe, ASTM A691 1-1/4Cr may be evaluated separately.

3. What is the UNS number for P11?

ASTM A335 P11 corresponds to UNS K11597.

4. What is the chemical composition of P11?

Key alloy limits include Cr 1.00–1.50% and Mo 0.44–0.65%, together with C 0.05–0.15%.

5. What are the minimum tensile and yield strengths of P11?

The minimum tensile strength is 415 MPa and the minimum yield strength is 205 MPa.

6. Is P11 elongation always 30% minimum?

No.

Elongation depends on specimen orientation and wall thickness. The applicable ASTM requirement should be used rather than one universal 30% figure.

7. Is P11 always normalized and tempered?

No.

P11 may be supplied full annealed, isothermal annealed, or normalized and tempered according to ASTM requirements.

8. What is the minimum tempering temperature for normalized-and-tempered P11?

The minimum tempering temperature for P11 in the normalized-and-tempered condition is 1200°F [650°C].

9. Does ASTM A335 require hydrostatic testing?

Yes. Current ASTM A335 requirements include hydrostatic testing of each length of pipe.

10. Does ASTM A335 P11 require NDE?

Yes. Each pipe is examined using an applicable nondestructive examination method according to ASTM A335 requirements.

11. What is the difference between P11 and P22?

P11 contains 1.00–1.50% Cr and 0.44–0.65% Mo, while P22 contains 1.90–2.60% Cr and 0.87–1.13% Mo.

The choice should be based on engineering design requirements rather than simply assuming P22 is "stronger."

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

No.

They belong to related Cr-Mo material families but have different manufacturing routes. A335 P11 is seamless; A691 1-1/4Cr is EFW welded pipe manufactured from pressure-vessel-quality plate.

13. What fittings are commonly used with P11 pipe?

ASTM A234 WP11 butt-weld fittings and ASTM A182 F11 forged components belong to corresponding 1.25Cr-0.5Mo material families.

Exact classes and heat-treatment conditions must follow the project specification.

14. Does P11 always require PWHT after welding?

Not as a universal ASTM A335 rule.

PWHT of fabrication welds depends on the governing construction code, wall thickness, service conditions, WPS/PQR and project requirements.

15. Is P11 suitable for hydrogen service?

It may be specified in selected hydrogen-containing systems, but suitability must be evaluated against operating temperature, hydrogen partial pressure and applicable project metallurgy requirements.

16. Can PMI be supplied?

Yes. PMI can be arranged where required to verify alloy grade and reduce the risk of material mix-up.

17. What sizes are available?

Common commercial sizes can include NPS 1/2–24 in. with SCH 40, 80, 120, 160, XS and XXS. Actual availability depends on wall thickness, quantity and mill capability.

18. What information is required for a quotation?

Provide the ASTM/ASME designation, NPS or OD, wall thickness, length, quantity, heat-treatment requirement, NDE/PMI requirements, documentation, third-party inspection requirements and delivery destination.

For an accurate technical and commercial quotation, please send:

ASTM A335 P11 / ASME SA335 P11
NPS / OD × Wall Thickness
Length & Quantity
Heat Treatment Requirement
NDE / PMI Requirements
MTC / TPI Requirements
Design Code / Project Specification
Delivery Destination

Xi'an Dongmeng Group Co., Ltd.

Phone / WhatsApp: +86 157 6921 4734
Email: office@dongmjd.com
Office: Room 4107, Runfeng Building, Sanqiao New Street, Weiyang District, Xi'an City, Shaanxi Province

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