ASTM A691 5Cr EFW Pipe

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Item	ASTM A691 5Cr EFW Pipe
Product	Electric-Fusion-Welded Alloy Steel Pipe
Standard	ASTM A691/A691M
Grade	5Cr
Alloy System	Approx. 5Cr-0.5Mo
Base Plate	ASTM A387/A387M Grade 5
UNS Reference	S50200 for A387 Grade 5
Manufacturing	EFW with filler metal
Nominal ASTM Scope	OD ≥ 16 in. [400 mm]
Nominal Wall Thickness Scope	Up to 3 in. [75 mm]
Common Classes	Class 22, 32, 42 and project-specified classes
Heat Treatment	Depends on ordered A691 class
Weld Examination	Radiography according to ordered class
Pressure Test	According to ordered class
Documentation	MTC / EN 10204 3.1, inspection reports and project documentation as required
Typical Applications	Refinery process piping, high-temperature pressure piping, heater and petrochemical systems

Important procurement note:
ASTM A691 5Cr is the material grade, while terms such as Class 22, Class 32 or Class 42 describe the manufacturing/inspection condition of the finished pipe. They must not be confused with ASTM A387 Grade 5 Plate Class 1 or Plate Class 2.

ASTM A691 covers carbon and alloy steel pipe manufactured by electric fusion welding with filler metal added from pressure-vessel-quality plate. The standard is intended for high-pressure service at elevated temperatures.

For Grade 5Cr:

ASTM A691 5Cr Pipe
→ manufactured from ASTM A387 Grade 5 plate
→ nominally 5% Cr + 0.5% Mo
→ formed into pipe
→ longitudinal seam welded using an electric-fusion welding process with filler metal
→ heat treated, examined and pressure tested according to the ordered A691 class.

This distinction is important because ASTM A691 does not simply describe "a welded version of P5 pipe." It is a separate product specification with its own plate source, class system, heat-treatment requirements and inspection framework.

ASTM A691 identifies 5Cr pipe as being produced from ASTM A387/A387M Grade 5 pressure-vessel plate. Current ASTM A387/A387M-25 describes Grade 5 as nominally 5.00% chromium and 0.50% molybdenum.

A commonly referenced A387 Grade 5 heat-analysis range is:

Element	Typical ASTM A387 Grade 5 Requirement
Carbon (C)	≤ 0.15%
Manganese (Mn)	0.30–0.60%
Silicon (Si)	≤ 0.50%
Phosphorus (P)	≤ 0.025%
Sulfur (S)	≤ 0.025%
Chromium (Cr)	4.00–6.00%
Molybdenum (Mo)	0.45–0.65%

Product-analysis tolerances can differ from heat-analysis limits. The chemistry accepted for a purchase order should therefore be verified against the specified ASTM edition and actual MTC, rather than relying only on a generic website table. Current A387 Grade 5 data continues to identify the material as a 5Cr-0.5Mo alloy.

The chromium content provides improved resistance to high-temperature oxidation and contributes to resistance in certain refinery environments, while molybdenum supports elevated-temperature strength.

However, ASTM A691 5Cr should not automatically be described as corrosion-resistant in every process medium. Actual suitability depends on temperature, pressure, sulfur activity, hydrogen partial pressure, process chemistry and applicable engineering code.

A common mistake on supplier websites is to publish one tensile-strength value as if it applied to every ASTM A691 5Cr pipe.

That is technically incomplete.

ASTM A691 5Cr uses A387 Grade 5 plate, and A387 Grade 5 itself can be supplied in two plate strength classes. ASTM A387/A387M-25 confirms that Grade 5 remains available in two tensile-strength classes.

Typical reference values are:

Base Plate Condition	Tensile Strength	Yield Strength, Min.	Elongation
A387 Grade 5 Class 1	415–585 MPa	205 MPa	18% min.
A387 Grade 5 Class 2	515–690 MPa	310 MPa	18% min.

Current 2025 material references report these Class 1 and Class 2 values for A387 Grade 5.

Do Not Confuse Plate Class with A691 Pipe Class

This point should be stated clearly in a purchase specification:

A387 Grade 5 Class 2 ≠ A691 5Cr Class 22.

The first relates to the strength class of the pressure-vessel plate.

The second relates to the heat treatment, radiographic examination and pressure testing of the manufactured pipe.

ASTM A691 uses a two-digit class system.

The first digit primarily identifies pipe heat treatment:

A691 Class Series	Pipe Heat Treatment
10–13	No pipe heat treatment
20–23	Stress relieved
30–33	Normalized
40–43	Normalized and tempered
50–53	Quenched and tempered

The second digit indicates the inspection/test combination:

Last Digit	Radiography	Pressure Test
0	No	No
1	Yes	No
2	Yes	Yes
3	No	Yes

ASTM publishes this class structure directly in the A691 specification. 

This is especially important because Class 22 is frequently misdescribed online.

ASTM A691 5Cr Class 22 means:

5Cr material grade

stress-relieved pipe

weld radiographically examined

pressure tested

It does not mean normalized and tempered.

Normalized-and-tempered pipe with radiography and pressure testing corresponds to Class 42 under the ASTM A691 class system.

For critical projects, the required class should therefore be stated explicitly on the RFQ and purchase order.

ASTM A691 nominally covers:

Outside Diameter:
16 in. [400 mm] and larger

Wall Thickness:
Up to 3 in. [75 mm], inclusive

ASTM also permits other dimensions when the pipe complies with the remaining requirements of the specification.

For project quotations, buyers should specify:

outside diameter

nominal or minimum wall thickness

required length

dimensional tolerance

pipe class

end preparation

quantity

design code

service temperature

operating medium

required NDE

documentation requirements

Large-diameter and non-standard wall combinations should be reviewed against plate availability, forming capability, welding procedure and heat-treatment capacity before production.

A properly controlled ASTM A691 5Cr production route typically includes:

1. ASTM A387 Grade 5 Plate Verification

Incoming pressure-vessel plate is checked for heat number, grade, plate class, chemistry, mechanical properties and traceability.

2. Plate Preparation

Plate edges are prepared according to the qualified welding procedure.

3. Forming

The plate is formed progressively into the specified pipe diameter while controlling ovality and alignment.

4. Longitudinal EFW Welding

The longitudinal joint is electric-fusion welded using added filler metal.

ASTM A691 is therefore fundamentally different from ERW pipe, where resistance heating and pressure produce the seam without the same filler-metal welding concept.

5. Weld Inspection

The longitudinal weld is examined according to the selected A691 class and project requirements.

6. Heat Treatment

Depending on the ordered class, the finished pipe may be:

untreated,

stress relieved,

normalized,

normalized and tempered, or

quenched and tempered.

7. Mechanical Testing

Applicable tensile and bend testing is performed in accordance with the specification and purchase requirements.

8. Pressure Testing

When specified by the selected class, pressure testing is carried out according to ASTM A691 requirements.

9. Dimensional Inspection

Typical checks include:

outside diameter

wall thickness

ovality

straightness

pipe length

weld profile

end condition

10. Final Identification and Documentation

Each shipment should maintain traceability between the pipe, heat number, plate certificate, manufacturing records and final MTC.

For refinery, petrochemical and pressure-piping projects, buyers usually need more than a simple dimensional certificate.

Dongmeng Group can coordinate inspection according to the ordered specification and project ITP.

Typical inspection items include:

Inspection Item	Purpose
Material Identification	Confirm correct 5Cr material
Chemical Analysis	Verify Cr-Mo chemistry
Tensile Test	Verify mechanical properties
Bend Test	Evaluate weld/joint integrity
Radiographic Examination	Examine longitudinal weld
Ultrasonic Examination	Additional examination where specified
Pressure Test	Verify pressure integrity when required
Dimensional Inspection	Confirm OD, WT, ovality and length
Visual Inspection	Check pipe and weld surface
PMI	Confirm alloy identity where specified
Hardness Testing	Available when required
Third-Party Inspection	SGS / BV / TÜV or nominated inspector where agreed

Inspection requirements should be defined before production, especially when project specifications impose requirements beyond basic ASTM A691.

 

For engineered pressure piping, traceability can be more important than simply receiving a certificate labeled "A691 5Cr."

A complete documentation package may include:

plate mill certificate

heat number

pipe identification number

welding procedure reference

heat-treatment record

NDE report

mechanical test report

hydrostatic/pressure test report

dimensional inspection report

final MTC

EN 10204 3.1 certification where specified

third-party inspection documentation

This allows procurement teams, EPC contractors and inspectors to trace the finished pipe back to the original plate heat.

A691 5Cr is primarily considered for large-diameter high-temperature pressure piping where a 5Cr-0.5Mo alloy system has been selected by the project engineer.

Typical applications include:

Petroleum Refineries

Used in selected high-temperature refinery process piping systems where increased chromium content is preferred over lower-Cr Cr-Mo materials.

Process Heaters

Large-diameter piping associated with heater and high-temperature process systems.

Petrochemical Plants

Process piping exposed to elevated temperatures and pressure.

High-Temperature Process Lines

Suitable where engineering specifications require 5Cr-0.5Mo alloy steel.

Pressure Equipment Connections

Large-diameter welded pipe may be selected for pressure equipment and process-system connections where ASTM A691 is permitted by the governing design code.

Material selection must still be based on the actual design code and service environment. ASTM A691 Grade 5Cr alone does not define the maximum allowable operating temperature or corrosion limit of a piping system.

These materials are chemically related, but they should not be treated as interchangeable product specifications.

Item	ASTM A691 5Cr	ASTM A335 P5
Product Type	Welded pipe	Seamless pipe
Manufacturing	EFW with filler metal	Seamless
Alloy Family	5Cr-0.5Mo	5Cr-0.5Mo
Typical Size Focus	Large diameter	Small to medium and other seamless sizes
Starting Material	Pressure-vessel-quality plate	Seamless pipe starting material
Weld Seam	Yes	No
A691 Class System	Yes	No
Typical Selection	Large-diameter engineered piping	Seamless high-temperature piping

A691 5Cr is particularly logical when the project requires:

large OD

heavy wall

5Cr-0.5Mo metallurgy

engineered longitudinal welded construction

specified heat treatment

documented weld NDE

pressure testing and project inspection

A335 P5 may be preferred when:

seamless construction is specifically required,

the required size is readily available as seamless pipe,

the piping class or project specification explicitly calls for ASTM A335 P5.

The final choice should be based on the project piping specification, design code and engineering approval-not only on alloy chemistry.

Grade	Nominal Cr-Mo System	General Procurement Position
A691 1-1/4Cr	~1.25Cr-0.5Mo	Lower-chromium Cr-Mo duty
A691 2-1/4Cr	~2.25Cr-1Mo	Widely used high-temperature Cr-Mo system
A691 3Cr	~3Cr-1Mo	Intermediate higher-Cr option
A691 5Cr	~5Cr-0.5Mo	Refinery/process applications requiring higher chromium
A691 9Cr	~9Cr-1Mo	Higher-chromium service
A691 Grade 91	Modified 9Cr-1Mo-V-Nb	Creep-strength-enhanced ferritic system

ASTM's plate-material table identifies these alloy families and specifically maps 5Cr to ASTM A387 Grade 5.

Do not select a higher chromium grade simply because it appears "better." Temperature, creep design, weldability, PWHT, process corrosion and project specifications all need to be considered.

5Cr-0.5Mo steel requires substantially more welding control than ordinary carbon steel.

Project welding procedures should address:

qualified WPS/PQR

suitable matching or specified filler metal

preheat requirement

interpass-temperature control

hydrogen control

weld consumable storage

heat input

PWHT where applicable

hardness control where required

weld NDE

repair-welding procedure

Actual preheat and PWHT temperatures should not be selected from a generic supplier webpage. They must follow the applicable material specification, qualified WPS, wall thickness, project specification and governing construction code.

This is especially important for thick-wall large-diameter Cr-Mo pipe.

 

A691 5Cr offers several practical advantages for engineered large-diameter piping:

5Cr-0.5Mo Alloy System
Provides the material characteristics required for selected elevated-temperature refinery and process services.

Large-Diameter Availability
EFW construction allows large OD and heavy-wall pipe sizes that can be difficult or uneconomical to manufacture seamlessly.

Defined Inspection Classes
ASTM A691 lets engineers specify heat treatment, radiography and pressure-test requirements through the pipe class.

Pressure-Vessel-Quality Plate Route
The finished pipe is manufactured from controlled pressure-vessel plate material.

Project-Based Manufacturing
Dimensions, heat treatment, examination and documentation can be coordinated around EPC and pressure-piping project requirements.

For an accurate ASTM A691 5Cr quotation, please send:

Standard: ASTM A691 / ASME SA-691

Grade: 5Cr

Required Pipe Class: e.g. Class 22 / 32 / 42

OD or NPS

Wall thickness

Length

Quantity / total tonnage

A387 base-plate class if specified

Service temperature

Design pressure

Process medium

Design code

Radiography / UT requirements

Impact-testing requirements if applicable

PMI / hardness / special testing requirements

MTC and third-party inspection requirements

End preparation

Packing requirements

Procurement Tip

Do not send an RFQ stating only:

"ASTM A691 5Cr Pipe."

For a technically correct quotation, at minimum specify:

ASTM A691 5Cr + Pipe Class + OD + WT + Length + Quantity + Inspection Requirements.

Dongmeng Group focuses on project-based supply of alloy steel piping for industrial and pressure-service applications.

For ASTM A691 5Cr projects, our supply process can cover:

material requirement review

plate-source verification

dimensional confirmation

EFW manufacturing coordination

heat-treatment requirements

weld examination

pressure testing

PMI and additional inspection

MTC documentation

third-party inspection

project packing

export delivery

For critical Cr-Mo piping, we recommend confirming the grade, A691 class, dimensions, service conditions and inspection requirements before quotation rather than quoting only by nominal pipe size.

1. What is ASTM A691 5Cr pipe?

ASTM A691 5Cr is an electric-fusion-welded chromium-molybdenum alloy steel pipe manufactured from pressure-vessel-quality plate for high-pressure service at elevated temperatures.

2. What material is used to manufacture A691 5Cr pipe?

ASTM A691 identifies 5Cr pipe with ASTM A387/A387M Grade 5 pressure-vessel plate, which has nominal alloy content of approximately 5% chromium and 0.5% molybdenum.

3. Is ASTM A691 5Cr seamless?

No. ASTM A691 5Cr is an EFW welded pipe. For a chemically related seamless product, ASTM A335 P5 may be considered where permitted by the project specification.

4. Is A691 5Cr the same as A335 P5?

No. They belong to a similar 5Cr-0.5Mo alloy family, but A691 5Cr is welded pipe manufactured from plate, while A335 P5 is seamless alloy steel pipe.

5. What does A691 5Cr Class 22 mean?

Class 22 means that the finished pipe is stress relieved, radiographically examined and pressure tested according to ASTM A691.

6. Is Class 22 normalized and tempered?

No. Under ASTM A691, normalized-and-tempered pipe belongs to the 40-series classes. Class 42 is normalized and tempered with radiography and pressure testing.

7. What is the difference between A691 Class 22 and A387 Class 2?

A691 Class 22 describes finished-pipe heat treatment and inspection. A387 Class 2 describes a higher tensile-strength class of the base pressure-vessel plate. They are completely different classification systems.

8. What is the standard size range of ASTM A691?

ASTM A691 nominally covers pipe 16 in. [400 mm] OD and larger with wall thickness up to 3 in. [75 mm]. Other dimensions may be supplied provided all applicable specification requirements are met.

9. Can ASTM A691 5Cr pipe be supplied with 100% radiography?

Yes, radiographic examination is incorporated into certain A691 classes. Additional examination requirements can also be specified in the purchase order where permitted.

10. Can PMI be provided?

Yes. Positive Material Identification can be specified as an additional project inspection requirement.

11. Can you provide EN 10204 3.1 certification?

EN 10204 3.1 documentation can be included when specified in the purchase contract and agreed before production.

12. Is A691 5Cr suitable for sour service?

5Cr chemistry alone does not establish sour-service suitability. H₂S conditions, hardness, heat treatment, welding, SSC/HIC requirements and the applicable NACE/ISO project specification must be reviewed separately.

13. What operating temperature can A691 5Cr withstand?

There is no single universal operating-temperature limit that should be assigned only from the ASTM grade. Allowable stress and operating limits depend on the governing design code, material condition, pressure, service environment and project design.

14. What information is most important when ordering A691 5Cr?

The most important items are the A691 class, OD, wall thickness, quantity, base-plate requirements, service conditions, NDE requirements and documentation package.

For fast technical review and quotation, send your piping schedule or RFQ with:

ASTM A691 5Cr | Class | OD | Wall Thickness | Length | Quantity | Design Temperature | Design Pressure | NDE | MTC / TPI Requirements

Dongmeng Group can review the specification before quotation and help identify missing information that could affect material selection, manufacturing route, inspection scope or delivery.

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