ASTM A988/A988M-23

Standard Specification for Hot Isostatically-Pressed Stainless Steel Flanges, Fittings, Valves, and Parts for High Temperature Service

ABSTRACT
This specification covers hot isostatically-pressed, powder metallurgy, stainless steel piping components such as flanges, fittings, valves, and similar parts, for use in pressure systems and temperature service applications. The specification includes several grades of martensitic, austenitic, age hardening, and austenitic-ferritic stainless steels. Compacts shall be manufactured by placing a single powder blend into a can, evacuating the can, and sealing it. The powder shall be prealloyed and made by a melting method (such as but not limited to air or vacuum induction melting, followed by gas atomization) to produce the specified chemical composition for carbon, manganese, phosphorus, sulfur, nickel, chromium, molybdenum, columbium, tantalum, copper, tungsten, and nitrogen. Other manufacturing requirements including compact homogeneity, microstructure, and can material removal are given. Heat treatment requirements, such as austenitizing or solutioning, cooling, quenching, tempering, and ageing, and structural integrity requirements, such as density, hydrostatic tests, and ultrasonic tests are detailed as well. Mechanical properties include tensile strength, yield strength, elongation, and hardness. Product analysis shall conform to the chemical requirements.
SCOPE
1.1 This specification covers hot isostatically-pressed, powder metallurgy, stainless steel piping components for use in pressure systems. Included are flanges, fittings, valves, and similar parts made to specified dimensions or to dimensional standards, such as in ASME specification B16.5.  
1.2 Several grades of martensitic, austenitic, age hardening, and austenitic-ferritic stainless steels are included in this specification.  
1.3 Supplementary requirements are provided for use when additional testing or inspection is desired. These shall apply only when specified individually by the purchaser in the order.  
1.4 This specification is expressed in both inch-pound units and in SI units. Unless the order specifies the applicable “M” specification designation (SI units), however, the material shall be furnished to inch-pound units.  
1.5 The values stated in either inch-pound units or SI units are to be regarded separately as the standard. Within the text, the SI units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.6 The following safety hazards caveat pertains only to test methods portions 8.1, 8.2, 9.5 – 9.7, and Section 10 of this specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 30-Apr-2023
• ICS: 23.040.40 - Metal fittings
• Technical Committee: A01 - Steel, Stainless Steel and Related Alloys
• Drafting Committee: A01.22 - Steel Forgings and Wrought Fittings for Piping Applications and Bolting Materials for Piping and Special Purpose Applications

Relations

• Refers: ASTM A941-24 - Standard Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
• Effective Date: 01-Mar-2024
• Refers: ASTM E340-23 - Standard Practice for Macroetching Metals and Alloys
• Effective Date: 15-Nov-2023
• Refers: ASTM A275/A275M-23 - Standard Practice for Magnetic Particle Examination of Steel Forgings
• Effective Date: 01-Nov-2023
• Refers: ASTM A745/A745M-20 - Standard Practice for Ultrasonic Examination of Austenitic Steel Forgings
• Effective Date: 01-May-2020
• Refers: ASTM A961/A961M-19a - Standard Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications<?Pub _bookmark Command="[Quick Mark]"?>
• Effective Date: 01-Nov-2019
• Refers: ASTM A941-17 - Standard Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
• Effective Date: 01-Sep-2017
• Refers: ASTM A961/A961M-16 - Standard Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications<?Pub _bookmark Command="[Quick Mark]"?>
• Effective Date: 01-Jun-2016
• Refers: ASTM A941-15 - Standard Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
• Effective Date: 01-Nov-2015
• Refers: ASTM A961/A961M-15 - Standard Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications<?Pub _bookmark Command="[Quick Mark]"?>
• Effective Date: 01-Nov-2015
• Refers: ASTM A745/A745M-15 - Standard Practice for Ultrasonic Examination of Austenitic Steel Forgings
• Effective Date: 01-May-2015
• Refers: ASTM A961/A961M-14 - Standard Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications<?Pub _bookmark Command="[Quick Mark]"?>
• Effective Date: 01-Nov-2014
• Refers: ASTM A751-14 - Standard Test Methods, Practices, and Terminology for Chemical Analysis of Steel Products
• Effective Date: 01-Mar-2014
• Refers: ASTM A961/A961M-13 - Standard Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping Applications<?Pub _bookmark Command="[Quick Mark]"?>
• Effective Date: 01-Oct-2013
• Refers: ASTM A941-13b - Standard Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
• Effective Date: 01-Jun-2013
• Refers: ASTM A262-13 - Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
• Effective Date: 01-May-2013

Overview

ASTM A988/A988M-23 is the standard specification governing hot isostatically-pressed (HIP), powder metallurgy, stainless steel piping components. This standard, issued by ASTM International, is essential for the production and procurement of flanges, fittings, valves, and similar parts designed for use in high temperature and pressure service environments. ASTM A988/A988M-23 covers several grades of martensitic, austenitic, age-hardening, and austenitic-ferritic stainless steels, offering specifications for chemical composition, manufacturing requirements, heat treatment, mechanical properties, and quality assurance testing.

By specifying uniform requirements for stainless steel HIP components, this standard assures reliability and safety for critical piping systems in demanding applications.

Key Topics

• Material Scope: Includes stainless steel flanges, fittings, valves, and parts produced by hot isostatic pressing using powder metallurgy techniques.
• Steel Grades: Covers martensitic, austenitic, age-hardening, and austenitic-ferritic stainless steels, designed for corrosion resistance and mechanical strength at elevated temperatures.
• Manufacturing Process:
  • Powder blends encapsulated in cans, evacuated, and sealed prior to consolidation by HIP.
  • Prealloyed powders created by air or vacuum induction melting, often followed by gas atomization.
  • Removal of can material using chemical or mechanical methods.
• Heat Treatment: Specifies requirements such as solution treating, austenitizing, quenching, tempering, and ageing for different stainless steel grades.
• Mechanical Properties: Components must meet requirements for tensile strength, yield strength, elongation, and hardness.
• Testing and Inspection: Includes requirements for density measurement, microstructural examination, hydrostatic tests, ultrasonic inspection, and, when specified, fatigue and corrosion testing.
• Supplementary Requirements: Allows purchasers to request additional testing or inspection per project needs, ensuring adaptability for specific engineering requirements.
• Unit System: Provides specifications in both inch-pound and SI units to cater to global industry practices.

Applications

Stainless steel HIP components standardized under ASTM A988/A988M-23 are widely used in:

• Petrochemical and Chemical Processing: Providing high-strength, corrosion-resistant piping components suitable for aggressive media and elevated pressure/temperature.
• Power Generation: Used in piping systems for high-temperature steam and process fluids.
• Oil & Gas: Suitable for refining, subsea, and offshore platforms where reliability in demanding environments is critical.
• Industrial Piping: Utilized in food processing, pharmaceuticals, water treatment, and other processing industries requiring clean, durable, and high-integrity components.
• High Temperature and Pressure Applications: Flanges, fittings, and valves produced according to this standard offer superior performance where mechanical integrity and safety are paramount.

Related Standards

For complete and compliant implementation, ASTM A988/A988M-23 references several critical standards, including:

• ASME B16.5: Dimensional standards for steel pipe flanges and flanged fittings.
• ASTM A262, A275/A275M, A745/A745M: Practices for corrosion, magnetic particle, and ultrasonic examination of stainless steels and forgings.
• ASTM A961/A961M: Common requirements specification for steel flanges, forged fittings, and valves in piping applications.
• ASME Specification IX: Welding qualifications for repair by welding.
• ASTM B311: Density testing for powder metallurgy materials.
• AWS A5.11, A5.14: Welding electrode specifications.
• ASTM E112, E165/E165M: Grain size determination and liquid penetrant testing.

Summary

ASTM A988/A988M-23 plays a crucial role in ensuring the quality, safety, and performance of hot isostatically-pressed stainless steel fittings, flanges, valves, and piping parts for high temperature service. Adherence to this standard provides users and manufacturers with confidence in the mechanical, chemical, and structural integrity of their components, ensuring durability and compliance across a wide range of rigorous industrial piping applications. For engineers, specifiers, and procurement professionals, ASTM A988/A988M-23 is an essential standard for sourcing high-quality HIP stainless steel components.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: A988/A988M − 23
Standard Specification for
Hot Isostatically-Pressed Stainless Steel Flanges, Fittings,
Valves, and Parts for High Temperature Service
This standard is issued under the fixed designation A988/A988M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
1.1 This specification covers hot isostatically-pressed, pow-
Barriers to Trade (TBT) Committee.
der metallurgy, stainless steel piping components for use in
pressure systems. Included are flanges, fittings, valves, and
2. Referenced Documents
similar parts made to specified dimensions or to dimensional
2.1 ASTM Standards:
standards, such as in ASME specification B16.5.
A262 Practices for Detecting Susceptibility to Intergranular
1.2 Several grades of martensitic, austenitic, age hardening,
Attack in Austenitic Stainless Steels
and austenitic-ferritic stainless steels are included in this
A275/A275M Practice for Magnetic Particle Examination of
specification.
Steel Forgings
1.3 Supplementary requirements are provided for use when
A745/A745M Practice for Ultrasonic Examination of Aus-
additional testing or inspection is desired. These shall apply
tenitic Steel Forgings
only when specified individually by the purchaser in the order.
A751 Test Methods and Practices for Chemical Analysis of
Steel Products
1.4 This specification is expressed in both inch-pound units
A923 Test Methods for Detecting Detrimental Intermetallic
and in SI units. Unless the order specifies the applicable “M”
Phase in Duplex Austenitic/Ferritic Stainless Steels
specification designation (SI units), however, the material shall
A941 Terminology Relating to Steel, Stainless Steel, Related
be furnished to inch-pound units.
Alloys, and Ferroalloys
1.5 The values stated in either inch-pound units or SI units
A961/A961M Specification for Common Requirements for
are to be regarded separately as the standard. Within the text,
Steel Flanges, Forged Fittings, Valves, and Parts for
the SI units are shown in brackets. The values stated in each
Piping Applications
system may not be exact equivalents; therefore, each system
B311 Test Method for Density of Powder Metallurgy (PM)
shall be used independently of the other. Combining values
Materials Containing Less Than Two Percent Porosity
from the two systems may result in non-conformance with the
E112 Test Methods for Determining Average Grain Size
standard.
E165/E165M Practice for Liquid Penetrant Testing for Gen-
1.6 The following safety hazards caveat pertains only to test
eral Industry
methods portions 8.1, 8.2, 9.5 – 9.7, and Section 10 of this
E340 Practice for Macroetching Metals and Alloys
specification: This standard does not purport to address all of
E606/E606M Test Method for Strain-Controlled Fatigue
the safety concerns, if any, associated with its use. It is the
Testing
responsibility of the user of this standard to establish appro-
G48 Test Methods for Pitting and Crevice Corrosion Resis-
priate safety, health, and environmental practices and deter-
tance of Stainless Steels and Related Alloys by Use of
mine the applicability of regulatory limitations prior to use.
Ferric Chloride Solution
1.7 This international standard was developed in accor-
2.2 MSS Standard:
dance with internationally recognized principles on standard-
SP 25 Standard Marking System for Valves, Fittings,
ization established in the Decision on Principles for the 3
Flanges, and Unions
1 2
This specification is under the jurisdiction of ASTM Committee A01 on Steel, For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
A01.22 onSteel Forgings and Wrought Fittings for Piping Applications and Bolting Standards volume information, refer to the standard’s Document Summary page on
Materials for Piping and Special Purpose Applications. the ASTM website.
Current edition approved May 1, 2023. Published May 2023. Originally Available from Manufacturers Standardization Society of the Valve and Fittings
approved in 1998. Last previous edition approved in 2017 as A988/A988M – 17. Industry (MSS), 127 Park St., NE, Vienna, VA 22180-4602, http://www.mss-
DOI: 10.1520/A0988_A0988M-23. hq.com.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A988/A988M − 23
2.3 ASME Specifications and Boiler and Pressure Vessel 4. Ordering Information
Codes:
4.1 It is the responsibility of the purchaser to specify in the
B16.5 Dimensional Standards for Steel Pipe Flanges and
purchase order all requirements that are necessary for material
Flanged Fittings
ordered under this specification. Such requirements may
2.4 ASME Specification IX Welding Qualifications:
include, but are not limited to, the following:
SFA-5.4 Specification for Corrosion-Resisting Chromium 4.1.1 Quantity (weight or number of parts),
and Chromium-Nickel Steel Covered Welding Electrodes
4.1.2 Name of material or UNS number,
SFA-5.9 Specification for Corrosion-Resisting Chromium
4.1.3 ASTM designation and year of issue,
and Chromium-Nickel Steel Welding Rods and Bare
4.1.4 Dimensions (tolerances and surface finishes should be
Electrodes
included),
SFA-5.11 Specification for Nickel and Nickel-Alloy Cov-
4.1.5 Microstructure examination if required (5.1.4),
ered Welding Electrodes
4.1.6 Inspection (15.1),
SFA-5.14 Specification for Nickel and Nickel Alloy Bare
4.1.7 Whether rough part or finished machined part (8.2.2),
Welding Electrodes and Rods
4.1.8 Supplementary requirements, if any,
2.5 AWS Standard: 4.1.9 Additional requirements (See 7.2 and 17.1), and
A5.11 Specification for Nickel and Nickel Alloy Welding
4.1.10 Requirement, if any, that the manufacturer shall
Electrodes for Shielded Metal Arc Welding submit drawings for approval showing the shape of the rough
A5.14 Specification for Nickel and Nickel Alloy Bare Weld-
part before machining and the exact location of test specimen
ing Electrodes and Rods material (See 9.3).
3. Terminology
5. Materials and Manufacture
3.1 Definitions—For definitions of terms used in this 5.1 Manufacturing Practice:
standard, refer to Terminology A941. 5.1.1 Compacts shall be manufactured by placing a single
powder blend into a can, evacuating the can, and sealing it. The
3.2 Definitions of Terms Specific to This Standard:
can material shall be selected to ensure that it has no deleteri-
3.2.1 can, n—the container used to encapsulate the powder
ous effect on the final product. The entire assembly shall be
during the pressure consolidation process; it is partially or fully
heated and placed under sufficient pressure for a sufficient
removed from the final part.
period of time to ensure that the final consolidated part meets
3.2.2 compact, n—the consolidated powder from one can. It
the density requirements of 8.1.1.1. One or more parts shall be
may be used to make one or more parts.
machined from a single compact.
3.2.3 consolidation, n—the bonding of adjacent powder 5.1.2 The powder shall be prealloyed and made by a melting
method capable of producing the specified chemical
particles in a compact under pressure by heating to a tempera-
ture below the melting point of the powder. composition, such as but not limited to, air or vacuum
induction melting, followed by gas atomization.
3.2.4 fill stem, n—the part of the compact used to fill the can.
5.1.3 When powder from more than one heat of the same
It is not usually integral to the part produced.
grade is used to make a blend, the heats shall be mixed
3.2.5 hot isostatic-pressing, n—a process for simultaneously
thoroughly to ensure homogeneity.
heating and forming a compact in which the powder is
5.1.4 The compact shall be sectioned and the microstructure
contained in a sealed formable enclosure usually made from
examined to check for porosity and other internal imperfec-
metal and the so-contained powder is subjected to equal
tions. It shall meet the requirements of 8.1.2. The sample shall
pressure from all directions at a temperature high enough to
be taken from the fill stem or from a location in a part as agreed
permit plastic deformation and consolidation of the powder
upon by the manufacturer and purchaser.
particles to take place.
5.1.5 Unless otherwise specified in the purchase order, the
3.2.6 lot, n—a number of parts made from a single powder manufacturer shall remove the can material from the surfaces
blend following the same manufacturing practice.
of the consolidated compacts by chemical or mechanical
methods such as by pickling or machining. This removal shall
3.2.7 part, n—a single item coming from a compact, either
be done before or after heat treatment at the option of the
prior to or after machining.
manufacturer (See Note 1).
3.2.8 powder blend, n—a homogeneous mixture of powder
NOTE 1—Often, it is advantageous to leave the can material in place
from one or more heats of the same grade.
until after heat treatment or further thermal processing of the consolidated
3.2.9 rough part, n—the part prior to final machining.
compact.
6. Chemical Composition
Available from American Society of Mechanical Engineers (ASME), ASME
6.1 The steel, both as a blend and as a part, shall conform to
International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
the requirements for chemical composition prescribed in Table
www.asme.org.
1. Test Methods, Practices, and Terminology of A751 shall
Available from American Welding Society (AWS), 8669 NW 36 St., #130,
Miami, FL 33166-6672, http://www.aws.org. apply.
A988/A988M − 23
TABLE 1 Chemical Requirements
A
Composition, %
UNS Other
D
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
Martensitic Stainless Steels
S41000 13 chromium 0.15 1.00 0.040 0.030 1.00 . . . 11.5–13.5 . . . . . . . . . . . .
S41026 13 chromium 0.15 1.00 0.020 0.020 1.00 1.00–2.00 11.5–13.5 0.40–0.60 0.50 . . . . . .
0.5 molybdenum
S41500 13 chromium, 4 0.05 0.50–1.00 0.030 0.030 0.60 3.5–5.5 11.5–14.0 0.50–1.00 . . . . . . . . .
nickel
S42390 12 chromium, 1.0 0.18–0.25 1.00 0.030 0.030 1.00 0.30–0.80 11.5–12.5 0.80–1.20 . . . 0.08–0.15 0.03–0.08 V 0.25–0.35
molybdenum,
modified with
vanadium
Austenitic Stainless Steels
N08028 32 nickel, 27 0.030 2.50 0.030 0.030 1.0 30.0–34.0 26.0–28.0 3.0–4.0 0.60–1.4 . . . . . .
chromium, 3.5
molybdenum
N08029 32 nickel, 27 0.020 2.0 0.025 0.015 0.6 30.0–34.0 26.0–28.0 4.0–5.0 0.60–1.4 . . . . . .
chromium, 4.5
molybdenum
S30400 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10
nickel
S30403 18 chromium, 8 0.035 2.00 0.045 0.030 1.00 8.0–13.0 18.0–20.0 . . . . . . . . . 0.10
nickel,
low carbon
S30451 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10–0.16
nickel,
modified with
nitrogen
S30453 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10–0.16
nickel,
modified with
nitrogen
S31600 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . 0.10
nickel,
modified with
molybdenum
S31603 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . 0.10
nickel,
modified with
molybdenum, low
carbon
S31651 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . 0.10–0.16
nickel,
modified with
molybdenum and
nitrogen
S31653 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . 0.10–0.16
nickel,
modified with
molybdenum and
nitrogen
S31700 19 chromium, 13 0.08 2.00 0.045 0.030 1.00 11.0–15.0 18.0–20.0 3.0–4.0 . . . . . . . . .
nickel
3.5 molybdenum
S31703 19 chromium, 13 0.030 2.00 0.045 0.030 1.00 11.0–15.0 18.0–20.0 3.0–4.0 . . . . . . . . .
nickel,
3.5 molybdenum
A988/A988M − 23
TABLE 1 Continued
A
Composition, %
UNS Other
D
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
S21904 20 chromium, 6 0.04 8.0–10.0 0.045 0.030 1.00 5.5–7.5 19.0–21.5 . . . . . . . . . 0.15–0.40
nickel, 9
manganese
S31254 20 chromium, 18 0.020 1.00 0.030 0.010 0.80 17.5–18.5 19.5–20.5 6.0–6.5 0.50–1.00 . . . 0.18–0.22
nickel, 6
molybdenum, low
carbon
S31725 19 chromium, 15 0.030 2.00 0.045 0.030 1.00 13.5–17.5 18.0–20.0 4.0–5.0 . . . . . . 0.20
nickel, 4
molybdenum
S31726 19 chromium, 15 0.030 2.00 0.045 0.030 1.00 14.5–17.5 17.0–20.0 4.0–5.0 . . . . . . 0.10–0.20
nickel, 4
molybdenum
N08367 22 chromium, 25 0.030 2.00 0.040 0.030 1.00 23.50– 20.0–22.0 6.0–7.0 0.75 . . . 0.18–0.25
nickel, 25.50
6.5 molybdenum,
low
carbon
S32654 25 chromium, 22 0.020 2.0–4.0 0.030 0.005 0.50 21.0–23.0 24.0–25.0 7.0–8.0 0.30–0.60 . . . 0.45–0.55
nickel,
7 molybdenum, low
carbon
Age-Hardening Stainless Steels
S17400 17 chromium, 4 0.07 1.00 0.040 0.030 1.00 3.0–5.0 15.0–17.5 . . . 3.0–5.0 0.15–0.45 . . .
nickel, 3 copper
Austenitic-Ferritic Stainless Steels
S31803 22 chromium, 5.5 0.030 2.00 0.030 0.020 1.00 4.5–6.5 21.0–23.0 2.5–3.5 . . . . . . 0.08–0.20
nickel,
modified with
nitrogen
S32205 22 chromium, 5.5 0.030 2.00 0.030 0.020 1.00 4.5–6.5 22.0–23.0 3.0–3.5 0.75 . . . 0.14–0.20
nickel, modified
with high nitrogen
S32906 29 chromium, 6.5 0.030 0.80–1.50 0.030 0.030 0.50 5.8–7.5 28.0–30.0 1.50–2.60 0.80 . . . 0.30–0.40
nickel, 2.0
molybdenum,
modified with high
nitrogen
S32950 26 chromium, 3.5 0.030 2.00 0.035 0.010 0.60 3.5–5.2 26.0–29.0 1.00–2.50 . . . . . . 0.15–0.35
nickel,
1.0 molybdenum
B
S32750 25 chromium, 7 0.030 1.20 0.035 0.020 0.80 6.0–8.0 24.0–26.0 3.0-5.0 0.50 . . . 0.24–0.32
nickel, 4
molybdenum,
modified with
nitrogen
S39274 25 chromium, 7 0.030 1.0 0.030 0.020 0.80 6.0–8.0 24.0–26.0 2.5–3.5 0.20–0.80 . . . 0.24–0.32 W
nickel, 1.50–2.50
modified with
nitrogen
and tungsten
A988/A988M − 23
TABLE 1 Continued
A
Composition, %
UNS Other
D
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
C
S32760 25 chromium, 7 0.030 1.00 0.030 0.010 1.00 6.0–8.0 24.0–26.0 3.0–4.0 0.50–1.00 . . . 0.20–0.30 W
nickel, 3.5 0.50–1.00
molybdenum,
modified with
nitrogen and
tungsten
S39277 25 chromium, 7 0.025 0.80 0.025 0.002 0.80 6.5–8.0 24.0–26.0 3.0–4.0 1.20–2.00 . . . 0.23–0.33 W
nickel, 0.80–1.20
3.7 molybdenum
S32505 27 chromium, 7 0.030 1.50 0.030 0.020 1.00 4.5–7.0 24.0–27.0 2.9–3.9 1.50–2.50 . . . 0.25–0.30
nickel, 3
molybdenum,
modified with
nitrogen and copper
A
Maximum, unless otherwise specified. Where ellipses (. . .) appear in this table, there is no requirement, and analysis for the element need not be determined or reported.
B
% Cr + 3.3 × % Mo + 16 × % N $ 41.
C
% Cr + 3.3 × (% Mo + 1/2 %W) + 16 × % N $ 41.
D
The terms Niobium (Nb) and Columbium (Cb) are alternate names for the same element.

A988/A988M − 23
6.1.1 A representative sample of each blend of powder shall 8.1.1.3 At the option of the producer, the density shall be
be analyzed by the manufacturer to determine the percentage of compared to the room temperature density typical of wrought
3 3
elements prescribed in Table 1. The blend shall conform to the steels of the same class of grades, 0.28 lb/in. [7.8 g/cm ] for
chemical composition requirements prescribed in Table 1. age-hardening, martensitic, and austenitic-ferritic grades, and
3 3
6.1.2 When required by the purchaser, the chemical com- 0.29 lb/in. [8.0 g/cm ] for austenitic grades, or to the density
position of a sample from one part from each lot of parts shall of a wrought reference sample of the same grade heat treated
be determined by the manufacturer. The composition of the in accordance with the requirements of Table 2 (See Note 2).
sample shall conform to the chemical requirements prescribed
NOTE 2—The actual density of stainless steel varies slightly with
in Table 1.
composition and heat treatment. For this reason, small differences in the
measured density from the typical density for a class of grades may be the
6.2 Addition of lead, selenium, or other unspecified ele-
result of differences in alloy content, heat treatment, or microporosity.
ments for the purpose of improving the machinability of the
When density values are measured that are less than the density typical of
compact shall not be permitted.
a class of grades, it is appropriate to examine the sample for microporosity
by the more specific metallographic examination procedures.
6.3 The steel shall not contain an unspecified element other
than nitrogen, for the ordered grade, to the extent that the steel 8.1.2 Microstructural Examination:
8.1.2.1 The microstructure shall be examined at 20-50×,
conforms to the requirements of another grade for which that
element is a specified element having a required minimum 100-200×, and 1000-2000× and shall be reasonably uniform
and shall be free of voids, laps, cracks, and porosity.
content.
8.1.2.2 One sample from each production lot shall be
7. Heat Treatment
examined. The sample shall be taken after hot-isostatic press-
ing or after final heat treatment. The sample shall be taken from
7.1 Except as provided in 7.2, the final heat treatment of all
the component, stem, protrusion, or test part made from a
parts shall be in compliance with the requirements of Table 2.
single powder blend consolidated in the same hot isostatic
After hot isostatic-pressing and prior to final heat treatment, the
press using the same pressure, temperature, and time param-
compacts are permitted to be annealed, at the option of the
eters and heat-treated in the same final heat-treatment charge.
producer, either as a part of the consolidation process or as a
The microstructure shall meet the requirements of 8.1.2.1.
separate operation.
8.1.2.3 If the sample fails to meet the requirements for
7.2 When agreed upon by the purchaser, liquid quenching
acceptance, each part in the lot is permitted to be retested and
may be applied to the martensitic stainless steels in place of the
those that pass shall be accepted.
furnace cool or air cool specified in Table 2, provided that such
8.2 Hydrostatic Tests—After they have been machined,
quenching is followed by tempering in the temperature ranges
pressure-containing parts shall be tested to the hydrostatic shell
as required in Table 2. Martensitic parts that are liquid
test pressures prescribed in ASME B16.5 for the applicable
quenched and tempered shall be marked “QT.”
steel rating for which the part is designed and shall show no
7.3 The final heat treatment shall be performed before or
leaks. Parts ordered under these specifications for working
after machining at the option of the producer.
pressures other than those listed in the ASME B16.5 ratings
7.4 See Section S16 if a particular heat treatment method is
shall be tested to such pressures as may be agreed upon
specified by the purchaser in the purchase order.
between the manufacturer and purchaser.
8.2.1 No hydrostatic test is required for weld neck or other
8. Structural Integrity Requirements
flanges.
8.1 Microporosity—The parts shall be free of microporosity
8.2.2 The compact manufacturer is not required to perform
as demonstrated by measurement of density as provided in
pressure tests on rough parts that are to be finish machined by
8.1.1 or by microstructural examination as provided in 8.1.2.
others. The fabricator of the finished part is not required to
8.1.1 Density Measurement:
pressure test parts that are designed to be pressure containing
8.1.1.1 The density measurement shall be used for accep-
only after assembly by welding into a larger structure. The
tance of material but not for rejection of material. The
manufacturer of the compacts, however, shall be responsible,
measured density for each production lot shall exceed 99 % of
as required in 16.1 for the satisfactory performance of the parts
the density typical of that grade when wrought and in the same
under the final test required in 8.2.
heat treated condition as the sample. A production lot that fails
8.3 Ultrasonic Tests—When specified in the order,
to meet this acceptance criterion is permitted to be tested at the
austenitic-ferritic stainless steel parts made from S32505 shall
option of the producer, for microporosity in accordance with
be ultrasonic tested according to the procedures described in
the microstructural examination as provided in 8.1.2.
Section S7.
8.1.1.2 Density shall be determined for one sample from
each production lot by measuring the difference in mass of the
9. Mechanical Properties
sample when weighed in air and when weighed in water and
9.1 The material shall conform to the requirements for
multiplying this difference by the density of water (Archi-
mechanical properties prescribed in Table 3 at room tempera-
mede’s principle). The equipment used shall be capable of
3 3 ture.
determining density within 60.004 lb/in. [0.10 g/cm ].
Alternatively, at the option of the producer, it is permitted to 9.2 Sample shall be from the component, stem, protrusion,
use Test Method B311 to determine the density. or test part made from a single powder blend consolidated in
A988/A988M − 23
TABLE 2 Heat Treating Requirements
Austenitizing/Solutioning Cooling Quenching, Cool Tempering Temperature,
UNS No. Heat Treat Type
A
Temperature °F [°C] Media to Below °F [°C] min° F [°C]
Martensitic Stainless Steels
B B
S41000 Class 1 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1325 [725]
B B
temper not required 1325 [725]
B B
S41000 Class 2 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1250 [675]
B B
temper not required 1250 [675]
B B
S41000 Class 3 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1100 [595]
B B
S41000 Class 4 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1000[540]
B B
S41026 anneal 1750 [955] furnace cool
normalize and temper 1750 [955] air cool 400 [205] 1150 [620]
S41500 normalize and temper 1850 [1010] air cool 200 [95] 1040–1120 [560–600]
S42390 normalize and temper 1860–1960 [1015–1070] air cool 200 [95] 1350–1440 [730–780]
Austenitic Stainless Steels
B
N08028 solution treat and quench 2000 [1100] liquid 500 [260]
B
N08029 solution treat and quench 2000 [1100] liquid 500 [260]
B
S30400 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30403 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30451 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30453 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31600 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31603 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31651 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31653 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31700 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31703 solution treat and quench 1900 [1040] liquid 500 [260]
B
S21904 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31254 solution treat and quench 2100 [1150] liquid 500 [260]
B
S31725 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31726 solution treat and quench 1900 [1040] liquid 500 [260]
B
N08367 solution treat and quench 2025 [1105] liquid 500 [260]
B
S32654 solution treat and quench 2050–2160 [1120–1180] liquid 500 [260]
Austenitic-Ferritic Stainless Steels
B
S31803 solution treat and quench 1870 [1020] liquid 500 [260]
B
S32205 solution treat and quench 1870 [1020] liquid 500 [260]
B
S32906 solution treat and quench 1850–2100 [1010–1150] liquid 500 [260]
C B
S32950 solution treat and quench 1825–1875 [995–1025] liquid 500 [260]
B
S32750 solution treat and quench 1880 [1025] liquid 500 [260]
B
S39274 solution treat and quench 1920–2060 [1050–1125] liquid 500 [260]
B
S32760 solution treat and quench 2010–2085 [1100–1140] liquid 500 [260]
B
S39277 solution treat and quench 1940 [1060] liquid 175 [80]
Age-Hardening Stainless Steels
D
Solution Heat Treatment Aging Heat Treatment
Cool as required Temperature °F [°C], time (h),
Condition Temperature °F [°C]
to below °F [°C] Required Cooling
S17400 A 1875-1975 [1025-1055] 90 [32] . . .
H900 1875-1975 [1025-1055] 90 [32] 900 [480], 1.0, air cool
H925 1875-1975 [1025-1055] 90 [32] 925 [495], 4.0, air cool
H1025 1875-1975 [1025-1055] 90 [32] 1025 [550], 4.0, air cool
H1075 1875-1975 [1025-1055] 90 [32] 1075 [580], 4.0, air cool
H1100 1875-1975 [1025-1055] 90 [32] 1100 [595], 4.0, air cool
H1150 1875-1975 [1025-1055] 90 [32] 1150 [620], 4.0, air cool
H1150M 1875-1975 [1025-1055] 90 [32] 1400 [760], 2.0, air c
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: A988/A988M − 17 A988/A988M − 23
Standard Specification for
Hot Isostatically-Pressed Stainless Steel Flanges, Fittings,
Valves, and Parts for High Temperature Service
This standard is issued under the fixed designation A988/A988M; the number immediately following the designation indicates the year
of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
A superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This specification covers hot isostatically-pressed, powder metallurgy, stainless steel piping components for use in pressure
systems. Included are flanges, fittings, valves, and similar parts made to specified dimensions or to dimensional standards, such
as in ASME specification B16.5.
1.2 Several grades of martensitic, austenitic, age hardening, and austenitic-ferritic stainless steels are included in this specification.
1.3 Supplementary requirements are provided for use when additional testing or inspection is desired. These shall apply only when
specified individually by the purchaser in the order.
1.4 This specification is expressed in both inch-pound units and in SI units. Unless the order specifies the applicable “M”
specification designation (SI units), however, the material shall be furnished to inch-pound units.
1.5 The values stated in either inch-pound units or SI units are to be regarded separately as the standard. Within the text, the SI
units are shown in brackets. The values stated in each system may not be exact equivalents; therefore, each system shall be used
independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.6 The following safety hazards caveat pertains only to test methods portions 8.1, 8.2, 9.5 – 9.7, and Section 10 of this
specification: This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appropriate safety and healthsafety, health, and environmental practices and
determine the applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A262 Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
A275/A275M Practice for Magnetic Particle Examination of Steel Forgings
A745/A745M Practice for Ultrasonic Examination of Austenitic Steel Forgings
This specification is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.22
onSteel Forgings and Wrought Fittings for Piping Applications and Bolting Materials for Piping and Special Purpose Applications.
Current edition approved May 1, 2017May 1, 2023. Published May 2017May 2023. Originally approved in 1998. Last previous edition approved in 20162017 as
A988/A988M – 16.A988/A988M – 17. DOI: 10.1520/A0988_A0988M-17.10.1520/A0988_A0988M-23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A988/A988M − 23
A751 Test Methods and Practices for Chemical Analysis of Steel Products
A923 Test Methods for Detecting Detrimental Intermetallic Phase in Duplex Austenitic/Ferritic Stainless Steels
A941 Terminology Relating to Steel, Stainless Steel, Related Alloys, and Ferroalloys
A961/A961M Specification for Common Requirements for Steel Flanges, Forged Fittings, Valves, and Parts for Piping
Applications
B311 Test Method for Density of Powder Metallurgy (PM) Materials Containing Less Than Two Percent Porosity
E112 Test Methods for Determining Average Grain Size
E165/E165M Practice for Liquid Penetrant Testing for General Industry
E340 Practice for Macroetching Metals and Alloys
E606/E606M Test Method for Strain-Controlled Fatigue Testing
G48 Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride
Solution
2.2 MSS Standard:
SP 25 Standard Marking System for Valves, Fittings, Flanges, and Unions
2.3 ASME Specifications and Boiler and Pressure Vessel Codes:
B16.5 Dimensional Standards for Steel Pipe Flanges and Flanged Fittings
2.4 ASME Specification IX Welding Qualifications:
SFA-5.4 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel Covered Welding Electrodes
SFA-5.9 Specification for Corrosion-Resisting Chromium and Chromium-Nickel Steel Welding Rods and Bare Electrodes
SFA-5.11 Specification for Nickel and Nickel-Alloy Covered Welding Electrodes
SFA-5.14 Specification for Nickel and Nickel Alloy Bare Welding Electrodes and Rods
2.5 AWS Standard:
A5.11 Specification for Nickel and Nickel Alloy Welding Electrodes for Shielded Metal Arc Welding
A5.14 Specification for Nickel and Nickel Alloy Bare Welding Electrodes and Rods
3. Terminology
3.1 Definitions—For definitions of terms used in this standard, refer to Terminology A941.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 can, n—the container used to encapsulate the powder during the pressure consolidation process; it is partially or fully
removed from the final part.
3.2.2 compact, n—the consolidated powder from one can. It may be used to make one or more parts.
3.2.3 consolidation, n—the bonding of adjacent powder particles in a compact under pressure by heating to a temperature below
the melting point of the powder.
3.2.4 fill stem, n—the part of the compact used to fill the can. It is not usually integral to the part produced.
3.2.5 hot isostatic-pressing, n—a process for simultaneously heating and forming a compact in which the powder is contained in
a sealed formable enclosure usually made from metal and the so-contained powder is subjected to equal pressure from all directions
at a temperature high enough to permit plastic deformation and consolidation of the powder particles to take place.
3.2.6 lot, n—a number of parts made from a single powder blend following the same manufacturing practice.
3.2.7 part, n—a single item coming from a compact, either prior to or after machining.
3.2.8 powder blend, n—a homogeneous mixture of powder from one or more heats of the same grade.
Available from Manufacturers Standardization Society of the Valve and Fittings Industry (MSS), 127 Park St., NE, Vienna, VA 22180-4602, http://www.mss-hq.com.
Available from American Society of Mechanical Engineers (ASME), ASME International Headquarters, Two Park Ave., New York, NY 10016-5990, http://
www.asme.org.
Available from American Welding Society (AWS), 8669 NW 36 St., #130, Miami, FL 33166-6672, http://www.aws.org.
A988/A988M − 23
3.2.9 rough part, n—the part prior to final machining.
4. Ordering Information
4.1 It is the responsibility of the purchaser to specify in the purchase order all requirements that are necessary for material ordered
under this specification. Such requirements may include, but are not limited to, the following:
4.1.1 Quantity (weight or number of parts),
4.1.2 Name of material or UNS number,
4.1.3 ASTM designation and year of issue,
4.1.4 Dimensions (tolerances and surface finishes should be included),
4.1.5 Microstructure examination if required (5.1.4),
4.1.6 Inspection (15.1),
4.1.7 Whether rough part or finished machined part (8.2.2),
4.1.8 Supplementary requirements, if any,
4.1.9 Additional requirements (See 7.2 and 17.1), and
4.1.10 Requirement, if any, that the manufacturer shall submit drawings for approval showing the shape of the rough part before
machining and the exact location of test specimen material (See 9.3).
5. Materials and Manufacture
5.1 Manufacturing Practice:
5.1.1 Compacts shall be manufactured by placing a single powder blend into a can, evacuating the can, and sealing it. The can
material shall be selected to ensure that it has no deleterious effect on the final product. The entire assembly shall be heated and
placed under sufficient pressure for a sufficient period of time to ensure that the final consolidated part meets the density
requirements of 8.1.1.1. One or more parts shall be machined from a single compact.
5.1.2 The powder shall be prealloyed and made by a melting method capable of producing the specified chemical composition,
such as but not limited to, air or vacuum induction melting, followed by gas atomization.
5.1.3 When powder from more than one heat of the same grade is used to make a blend, the heats shall be mixed thoroughly to
ensure homogeneity.
5.1.4 The compact shall be sectioned and the microstructure examined to check for porosity and other internal imperfections. It
shall meet the requirements of 8.1.2. The sample shall be taken from the fill stem or from a location in a part as agreed upon by
the manufacturer and purchaser.
5.1.5 Unless otherwise specified in the purchase order, the manufacturer shall remove the can material from the surfaces of the
consolidated compacts by chemical or mechanical methods such as by pickling or machining. This removal shall be done before
or after heat treatment at the option of the manufacturer (See Note 1).
NOTE 1—Often, it is advantageous to leave the can material in place until after heat treatment or further thermal processing of the consolidated compact.
6. Chemical Composition
6.1 The steel, both as a blend and as a part, shall conform to the requirements for chemical composition prescribed in Table 1.
Test Methods, Practices, and Terminology of A751 shall apply.
A988/A988M − 23
TABLE 1 Chemical Requirements
A
Composition, %
UNS Other
ED
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
Martensitic Stainless Steels
S41000 13 chromium 0.15 1.00 0.040 0.030 1.00 . . . 11.5–13.5 . . . . . . . . . . . .
S41026 13 chromium 0.15 1.00 0.020 0.020 1.00 1.00–2.00 11.5–13.5 0.40–0.60 0.50 . . . . . .
0.5 molybdenum
S41500 13 chromium, 4 0.05 0.50–1.00 0.030 0.030 0.60 3.5–5.5 11.5–14.0 0.50–1.00 . . . . . . . . .
nickel
S42390 12 chromium, 1.0 0.18–0.25 1.00 0.030 0.030 1.00 0.30–0.80 11.5–12.5 0.80–1.20 . . . 0.08–0.15 0.03–0.08 V 0.25–0.35
molybdenum,
modified with
vanadium
Austenitic Stainless Steels
N08028 32 nickel, 27 0.030 2.50 0.030 0.030 1.0 30.0–34.0 26.0–28.0 3.0–4.0 0.60–1.4 . . . . . .
chromium, 3.5
molybdenum
N08029 32 nickel, 27 0.020 2.0 0.025 0.015 0.6 30.0–34.0 26.0–28.0 4.0–5.0 0.60–1.4 . . . . . .
chormium, 4.5
molybdenum
N08029 32 nickel, 27 0.020 2.0 0.025 0.015 0.6 30.0–34.0 26.0–28.0 4.0–5.0 0.60–1.4 . . . . . .
chromium, 4.5
molybdenum
B
S30400 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . . . .
nickel
S30400 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10
nickel
B
S30403 18 chromium, 8 0.035 2.00 0.045 0.030 1.00 8.0–13.0 18.0–20.0 . . . . . . . . . . . .
nickel,
low carbon
S30403 18 chromium, 8 0.035 2.00 0.045 0.030 1.00 8.0–13.0 18.0–20.0 . . . . . . . . . 0.10
nickel,
low carbon
C
S30451 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . . . .
nickel,
modified with
nitrogen
S30451 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10–0.16
nickel,
modified with
nitrogen
S30453 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . . . .
nickel,
modified with
nitrogen
S30453 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 8.0–11.0 18.0–20.0 . . . . . . . . . 0.10–0.16
nickel,
modified with
nitrogen
B
S31600 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . . . .
nickel,
modified with
molybdenum
S31600 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . 0.10
nickel,
modified with
molybdenum
A988/A988M − 23
TABLE 1 Continued
A
Composition, %
UNS Other
ED
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
B
S31603 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . . . .
nickel,
modified with
molybdenum, low
carbon
S31603 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–14.0 16.0–18.0 2.00–3.00 . . . . . . 0.10
nickel,
modified with
molybdenum, low
carbon
C
S31651 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . . . .
nickel,
modified with
molybdenum and
nitrogen
S31651 18 chromium, 8 0.08 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . 0.10–0.16
nickel,
modified with
molybdenum and
nitrogen
C
S31653 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . . . .
nickel,
modified with
molybdenum and
nitrogen
S31653 18 chromium, 8 0.030 2.00 0.045 0.030 1.00 10.0–13.0 16.0–18.0 2.00–3.00 . . . . . . 0.10–0.16
nickel,
modified with
molybdenum and
nitrogen
S31700 19 chromium, 13 0.08 2.00 0.045 0.030 1.00 11.0–15.0 18.0–20.0 3.0–4.0 . . . . . . . . .
nickel
3.5 molybdenum
S31703 19 chromium, 13 0.030 2.00 0.045 0.030 1.00 11.0–15.0 18.0–20.0 3.0–4.0 . . . . . . . . .
nickel,
3.5 molybdenum
S21904 20 chromium, 6 0.04 8.0–10.0 0.045 0.030 1.00 5.5–7.5 19.0–21.5 . . . . . . . . . 0.15–0.40
nickel, 9
manganese
S31254 20 chromium, 18 0.020 1.00 0.030 0.010 0.80 17.5–18.5 19.5–20.5 6.0–6.5 0.50–1.00 . . . 0.18–0.22
nickel, 6
molybdenum, low
carbon
S31725 19 chromium, 15 0.030 2.00 0.045 0.030 1.00 13.5–17.5 18.0–20.0 4.0–5.0 . . . . . . 0.20
nickel, 4
molybdenum
S31726 19 chromium, 15 0.030 2.00 0.045 0.030 1.00 14.5–17.5 17.0–20.0 4.0–5.0 . . . . . . 0.10–0.20
nickel, 4
molybdenum
N08367 22 chromium, 25 0.030 2.00 0.040 0.030 1.00 23.50– 20.0–22.0 6.0–7.0 0.75 . . . 0.18–0.25
nickel, 25.50
6.5 molybdenum,
low
carbon
A988/A988M − 23
TABLE 1 Continued
A
Composition, %
UNS Other
ED
Grade Carbon Manganese Phosphorus Sulfur Silicon Nickel Chromium Molybdenum Copper Niobium Nitrogen
Designation Elements
S32654 25 chromium, 22 0.020 2.0–4.0 0.030 0.005 0.50 21.0–23.0 24.0–25.0 7.0–8.0 0.30–0.60 . . . 0.45–0.55
nickel,
7 molybdenum, low
carbon
Age-Hardening Stainless Steels
S17400 17 chromium, 4 0.07 1.00 0.040 0.030 1.00 3.0–5.0 15.0–17.5 . . . 3.0–5.0 0.15–0.45 . . .
nickel, 3 copper
Austenitic-Ferritic Stainless Steels
S31803 22 chromium, 5.5 0.030 2.00 0.030 0.020 1.00 4.5–6.5 21.0–23.0 2.5–3.5 . . . . . . 0.08–0.20
nickel,
modified with
nitrogen
S32205 22 chromium, 5.5 0.030 2.00 0.030 0.020 1.00 4.5–6.5 22.0–23.0 3.0–3.5 0.75 . . . 0.14–0.20
nickel, modified
with high nitrogen
S32906 29 chromium, 6.5 0.030 0.80–1.50 0.030 0.030 0.50 5.8–7.5 28.0–30.0 1.50–2.60 0.80 . . . 0.30–0.40
nickel, 2.0
molybdenum,
modified with high
nitrogen
S32950 26 chromium, 3.5 0.030 2.00 0.035 0.010 0.60 3.5–5.2 26.0–29.0 1.00–2.50 . . . . . . 0.15–0.35
nickel,
1.0 molybdenum
B
S32750 25 chromium, 7 0.030 1.20 0.035 0.020 0.80 6.0–8.0 24.0–26.0 3.0-5.0 0.50 . . . 0.24–0.32
nickel, 4
molybdenum,
modified with
nitrogen
S39274 25 chromium, 7 0.030 1.0 0.030 0.020 0.80 6.0–8.0 24.0–26.0 2.5–3.5 0.20–0.80 . . . 0.24–0.32 W
nickel, 1.50–2.50
modified with
nitrogen
and tungsten
D
S32760 25 chromium, 7 0.030 1.00 0.030 0.010 1.00 6.0–8.0 24.0–26.0 3.0–4.0 0.50–1.00 . . . 0.20–0.30 W
nickel, 3.5 0.50–1.00
molybdenum,
modified with
nitrogen and
tungsten
C
S32760 25 chromium, 7 0.030 1.00 0.030 0.010 1.00 6.0–8.0 24.0–26.0 3.0–4.0 0.50–1.00 . . . 0.20–0.30 W
nickel, 3.5 0.50–1.00
molybdenum,
modified with
nitrogen and
tungsten
S39277 25 chromium, 7 0.025 0.80 0.025 0.002 0.80 6.5–8.0 24.0–26.0 3.0–4.0 1.20–2.00 . . . 0.23–0.33 W
nickel, 0.80–1.20
3.7 molybdenum
S32505 27 chromium, 7 0.030 1.50 0.030 0.020 1.00 4.5–7.0 24.0–27.0 2.9–3.9 1.50–2.50 . . . 0.25–0.30
nickel, 3
molybdenum,
modified with
nitrogen and copper
A
Maximum, unless otherwise specified. Where ellipses (. . .) appear in this table, there is no requirement, and analysis for the element need not be determined or reported.
B
S30400, S30403, S31600, and S31603 shall have a maximum nitrogen content of 0.10 %.

A988/A988M − 23
C
S30451, S31651, S30453, S31653 shall have a nitrogen content of 0.10 to 0.16 %.
B
% Cr + 3.3 × % Mo + 16 × % N > 40 min.$ 41.
C
% Cr + 3.3 × (% Mo + 1/2 %W) + 16 × % N $ 41.
D
The The terms Niobium (Nb) and Columbium (Cb) are alternate names for the same element.

A988/A988M − 23
6.1.1 A representative sample of each blend of powder shall be analyzed by the manufacturer to determine the percentage of
elements prescribed in Table 1. The blend shall conform to the chemical composition requirements prescribed in Table 1.
6.1.2 When required by the purchaser, the chemical composition of a sample from one part from each lot of parts shall be
determined by the manufacturer. The composition of the sample shall conform to the chemical requirements prescribed in Table
1.
6.2 Addition of lead, selenium, or other unspecified elements for the purpose of improving the machinability of the compact shall
not be permitted.
6.3 The steel shall not contain an unspecified element other than nitrogen, for the ordered grade, to the extent that the steel
conforms to the requirements of another grade for which that element is a specified element having a required minimum content.
7. Heat Treatment
7.1 Except as provided in 7.2, the final heat treatment of all parts shall be in compliance with the requirements of Table 2. After
hot isostatic-pressing and prior to final heat treatment, the compacts are permitted to be annealed, at the option of the producer,
either as a part of the consolidation process or as a separate operation.
7.2 When agreed upon by the purchaser, liquid quenching may be applied to the martensitic stainless steels in place of the furnace
cool or air cool specified in Table 2, provided that such quenching is followed by tempering in the temperature ranges as required
in Table 2. Martensitic parts that are liquid quenched and tempered shall be marked “QT.”
7.3 The final heat treatment shall be performed before or after machining at the option of the producer.
7.4 See Section S16 if a particular heat treatment method is specified by the purchaser in the purchase order.
8. Structural Integrity Requirements
8.1 Microporosity—The parts shall be free of microporosity as demonstrated by measurement of density as provided in 8.1.1 or
by microstructural examination as provided in 8.1.2.
8.1.1 Density Measurement:
8.1.1.1 The density measurement shall be used for acceptance of material but not for rejection of material. The measured density
for each production lot shall exceed 99 % of the density typical of that grade when wrought and in the same heat treated condition
as the sample. A production lot that fails to meet this acceptance criterion is permitted to be tested at the option of the producer,
for microporosity in accordance with the microstructural examination as provided in 8.1.2.
8.1.1.2 Density shall be determined for one sample from each production lot by measuring the difference in mass of the sample
when weighed in air and when weighed in water and multiplying this difference by the density of water (Archimede’s principle).
3 3
The equipment used shall be capable of determining density within 60.004 lb/in. [0.10 g/cm ]. Alternatively, at the option of the
producer, it is permitted to use Test Method B311 to determine the density.
8.1.1.3 At the option of the producer, the density shall be compared to the room temperature density typical of wrought steels of
3 3 3
the same class of grades, 0.28 lb/in. [7.8 g/cm ] for age-hardening, martensitic, and austenitic-ferritic grades, and 0.29 lb/in. [8.0
g/cm ] for austenitic grades, or to the density of a wrought reference sample of the same grade heat treated in accordance with
the requirements of Table 2 (See Note 2).
NOTE 2—The actual density of stainless steel varies slightly with composition and heat treatment. For this reason, small differences in the measured
density from the typical density for a class of grades may be the result of differences in alloy content, heat treatment, or microporosity. When density
values are measured that are less than the density typical of a class of grades, it is appropriate to examine the sample for microporosity by the more specific
metallographic examination procedures.
8.1.2 Microstructural Examination:
A988/A988M − 23
TABLE 2 Heat Treating Requirements
Austenitizing/Solutioning Cooling Quenching, Cool Tempering Temperature,
UNS No. Heat Treat Type
A
Temperature °F [°C] Media to Below °F [°C] min° F [°C]
Martensitic Stainless Steels
B B
S41000 Class 1 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1325 [725]
B B
temper not required 1325 [725]
B B
S41000 Class 2 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1250 [675]
B B
temper not required 1250 [675]
B B
S41000 Class 3 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1100 [595]
B B
S41000 Class 4 anneal not specified furnace cool
normalize and temper not specified air cool 400 [205] 1000[540]
B B
S41026 anneal 1750 [955] furnace cool
normalize and temper 1750 [955] air cool 400 [205] 1150 [620]
S41500 normalize and temper 1850 [1010] air cool 200 [95] 1040–1120 [560–600]
S42390 normalize and temper 1860–1960 [1015–1070] air cool 200 [95] 1350–1440 [730–780]
Austenitic Stainless Steels
B
N08028 solution treat and quench 2000 [1100] liquid 500 [260]
B
N08029 solution treat and quench 2000 [1100] liquid 500 [260]
B
S30400 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30403 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30451 solution treat and quench 1900 [1040] liquid 500 [260]
B
S30453 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31600 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31603 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31651 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31653 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31700 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31703 solution treat and quench 1900 [1040] liquid 500 [260]
B
S21904 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31254 solution treat and quench 2100 [1150] liquid 500 [260]
B
S31725 solution treat and quench 1900 [1040] liquid 500 [260]
B
S31726 solution treat and quench 1900 [1040] liquid 500 [260]
B
N08367 solution treat and quench 2025 [1105] liquid 500 [260]
B
S32654 solution treat and quench 2050–2160 [1120–1180] liquid 500 [260]
Austenitic-Ferritic Stainless Steels
B
S31803 solution treat and quench 1870 [1020] liquid 500 [260]
B
S32205 solution treat and quench 1870 [1020] liquid 500 [260]
B
S32906 solution treat and quench 1850–2100 [1010–1150] liquid 500 [260]
C B
S32950 solution treat and quench 1825–1875 [995–1025] liquid 500 [260]
B
S32750 solution treat and quench 1880 [1025] liquid 500 [260]
B
S39274 solution treat and quench 1920–2060 [1050–1125] liquid 500 [260]
B
S32760 solution treat and quench 2010–2085 [1100–1140] liquid 500 [260]
B
S39277 solution treat and quench 1940 [1060] liquid 175 [80]
Age-Hardening Stainless Steels
D
Solution Heat Treatment Aging Heat Treatment
Cool as required Temperature °F [°C], time (h),
Condition Temperature °F [°C]
to below °F [°C] Required Cooling
S17400 A 1875-1975 [1025-1055] 90 [32] . . .
H900 1875-1975 [1025-1055] 90 [32] 900 [480], 1.0, air cool
H925 1875-1975 [1025-1055] 90 [32] 925 [495], 4.0, air cool
H1025 1875-1975 [1025-1055] 90 [32] 1025 [550], 4.0, air cool
H1075 1875-1975 [1025-1055] 90 [32] 1075 [580], 4.0, air cool
H1100 1875-1975 [1025-1055] 90 [32] 1100 [595], 4.0, air cool
H1150 1875-1975 [1025-1055] 90 [32] 1150 [620], 4.0, air cool
H1150M 1875-1975 [1025-1055] 90 [32] 1400 [760], 2.0, air cool
plus 1150 [620], 4.0, air cool
A
Minimum unless temperature range is listed.
B
Not applicable.
C
30 min/in. of thickness.
D
Unless otherwise noted, it is permitted to vary the aging treatment temperature to obtain the required properties. The listed times are minimum time at temperature and
the treatment is permitted to be extended to obtain the required ductility. Material treated at an intermediate temperature must meet the ductility requirements of the next
higher hardening or aging temperature, or both.
8.1.2.1 The microstructure shall be examined at 20-50×, 100-200×, and 1000-2000× and shall be reasonably uniform and shall
be free of voids, laps, cracks, and porosity.
8.1.2.2 One sample from each production lot shall be examined. The sample shall be taken after hot-isostatic pressing or after final
heat treatment. The sample shall be taken from the component, stem, protrusion, or test part made from a single powder blend
A988/A988M − 23
consolidated in the same hot isostatic press using the same pressure, temperature, and time parameters and heat-treated in the same
final heat-treatment charge. The microstructure shall meet the requirements of 8.1.2.1.
8.1.2.3 If the sample fails to meet the requirements for acceptance, each part in the lot is permitted to be retested and those that
pass shall be accepted.
8.2 Hydrostatic Tests—After they have been machined, pressure-containing parts shall be tested to the hydrostatic shell test
pressures prescribed in ASME B16.5 for the applicable steel rating for which the part is designed and shall show no leaks. Parts
ordered under these specifications for working pressures other than those listed in the ASME B16.5 ratings shall be tested to such
pressures as may be agreed upon between the manufacturer and purchaser.
8.2.1 No hydrostatic test is required for weld neck or other flanges.
8.2.2 The compact manufacturer is not required to perform pressure tests on rough parts that are to be finish machined by others.
The fabricator of the finished part is not required to pressure test parts that are designed to be pressure containing only after
assembly by welding into a larger stru
...