ASTM A193 Standard Specification for High-Temperature and High-Pressure Bolting
ASTM A193/A193M is the standard specification for alloy steel and stainless steel bolting materials and bolting components used in pressure vessels, valves, flanges and fittings operating under high-temperature, high-pressure or other special service conditions.
The specification covers several ferritic alloy steel and austenitic stainless steel grades. Common examples include ASTM A193 Grade B7, B7M, B8, B8M and B16. The correct grade must be selected according to the design temperature, pressure, corrosion environment, mechanical properties and applicable project specification.
ASTM A193 should be used together with ASTM A962/A962M, which establishes common requirements for bolting materials and components. Dimensional, thread and nut requirements are normally controlled by separate ASTM, ASME or project standards.
What Is ASTM A193?
ASTM A193 is formally titled:
Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service and Other Special Purpose Applications.
It is primarily used for engineered bolting installed in:
- Pressure vessels
- Pipe flanges
- Industrial valves
- Pipe fittings
- Heat exchangers
- Boilers
- Refinery equipment
- Petrochemical piping
- Offshore facilities
- Power-generation systems
Unlike a general commercial fastener specification, ASTM A193 establishes requirements for bolting intended for demanding service conditions where material strength, heat treatment, hardness and traceability are critical.
The standard covers both bolting materials and finished bolting components. Bars and wire must be hot-wrought and may subsequently be processed by methods such as centerless grinding or cold drawing.
Products Covered by ASTM A193
ASTM A193 material is commonly manufactured into:
- Fully threaded stud bolts
- Continuous-thread studs
- Double-end studs
- Tap-end studs
- Hex bolts
- Heavy hex bolts
- Cap screws
- Threaded rods
- Custom bolting components
- Bars and wire for subsequent fastener production
For flange bolting, fully threaded studs supplied with two heavy hex nuts are among the most common configurations.
ASTM A193 defines the material and performance requirements. It does not independently establish every dimensional detail of the finished fastener.
For example, ASME B18.31.2 covers dimensional and general requirements for continuous-thread studs, double-end studs and flange stud bolts. ASME B1.1 establishes unified inch thread forms, series, classes, allowances and tolerances. (美国机械工程师协会)
Common ASTM A193 Grades
The following table provides a practical comparison of frequently specified ASTM A193 grades.
| ASTM A193 Grade | Material Type | Principal Characteristic | Typical Service | Common Matching Nut |
|---|---|---|---|---|
| B7 | Chromium-molybdenum alloy steel | High tensile strength after quenching and tempering | High-pressure and elevated-temperature piping | ASTM A194 Grade 2H |
| B7M | Chromium-molybdenum alloy steel with controlled hardness | Lower maximum hardness than conventional B7 | Sour service and projects with hardness restrictions | ASTM A194 Grade 2HM |
| B8 Class 1 | Type 304 austenitic stainless steel | Solution-treated condition with corrosion resistance | Chemical and moderately corrosive service | ASTM A194 Grade 8 |
| B8 Class 2 | Strain-hardened Type 304 stainless steel | Higher strength than Class 1 | Applications requiring increased stainless steel strength | ASTM A194 Grade 8 |
| B8M Class 1 | Type 316 austenitic stainless steel | Improved resistance in chloride-containing environments | Marine, chemical and corrosive service | ASTM A194 Grade 8M |
| B8M Class 2 | Strain-hardened Type 316 stainless steel | Higher strength with Type 316 corrosion resistance | Higher-load corrosive applications | ASTM A194 Grade 8M |
| B16 | Chromium-molybdenum-vanadium alloy steel | Designed for higher-temperature performance | Power generation and high-temperature equipment | Selected by project specification |
This table is an engineering selection summary rather than a substitute for the applicable edition of ASTM A193. Final grade selection must consider the design code, operating temperature, bolt diameter, required mechanical properties and service environment. ASTM states that grade selection depends on design, service conditions, mechanical properties and high-temperature characteristics. (ASTM Store)
ASTM A193 B7 vs B7M
ASTM A193 Grade B7 is a quenched-and-tempered alloy steel grade widely used for high-pressure and elevated-temperature flange connections. It is commonly paired with ASTM A194 Grade 2H heavy hex nuts.
ASTM A193 Grade B7M has a similar alloy-steel basis but is produced with more restrictive hardness controls. It is commonly specified where resistance to sulfide stress cracking or compliance with project-specific sour-service requirements is required.
B7M should not automatically be described as NACE compliant solely because of its grade designation. Compliance must be evaluated against the applicable operating environment, hardness limits, manufacturing route, certification requirements and the specified edition of NACE MR0175/ISO 15156.
ISO 15156 addresses the selection and qualification of metallic materials used in oil and gas production equipment exposed to H₂S-containing environments. It supplements rather than replaces applicable design codes and material specifications.
ASTM A193 B8 vs B8M
The primary difference between B8 and B8M is the stainless steel type:
- B8 is based on Type 304 austenitic stainless steel.
- B8M is based on Type 316 austenitic stainless steel.
- B8M is generally selected where improved resistance to chlorides and more aggressive corrosion conditions is required.
- Both grades may be supplied in different classes depending on the required heat-treatment condition and strength level.
Class 1 generally represents the solution-treated condition, while Class 2 obtains increased strength through strain hardening. The class must be clearly stated in the purchase order because mechanical properties and size limitations may differ.
Manufacturing and Heat Treatment
ASTM A193 manufacturing requirements vary according to the selected material grade.
Ferritic Alloy Steel Bolting
Ferritic alloy steel grades must receive heat treatment suitable for their intended high-temperature characteristics. Depending on the grade, this may include:
- Austenitizing
- Quenching
- Tempering
- Controlled cooling
- Final hardness verification
ASTM requires ferritic materials to be properly heat treated, and the material must cool below the transformation range after rolling or forging before subsequent heat treatment. (ASTM Store)
Austenitic Stainless Steel Bolting
Austenitic stainless steel grades may be supplied in:
- Carbide solution-treated condition
- Solution-treated and strain-hardened condition
When strain-hardened stainless steel is ordered, the purchaser must clearly define the required grade, class, diameter and mechanical-property requirements.
Thread Manufacturing
Threads may be produced by:
- Thread rolling
- Thread cutting
- Machining
- Grinding where specifically required
The permitted process should be confirmed against the purchase specification, size, heat-treatment sequence and coating requirements.
Chemical Composition Requirements
Each ASTM A193 grade has defined chemical-composition limits. Depending on the grade, controlled elements may include:
- Carbon
- Manganese
- Phosphorus
- Sulfur
- Silicon
- Chromium
- Molybdenum
- Nickel
- Vanadium
- Other grade-specific alloying elements
The material must conform to the composition specified for the ordered grade. ASTM also restricts the use of unspecified alloying elements where their presence could cause the material to conform to another designated grade. (ASTM Store)
Chemical analysis is normally verified through:
- Heat analysis
- Product analysis when required
- Heat-number traceability
- Review of the material test certificate
Detailed composition tables should be checked against the exact edition specified in the purchase order.
Mechanical Property Requirements
ASTM A193 establishes grade- and size-dependent requirements for properties including:
- Tensile strength
- Yield strength
- Elongation
- Reduction of area
- Hardness
- Full-size fastener tensile performance
- Wedge tensile performance where applicable
Mechanical-property limits may change according to:
- Material grade
- Grade class
- Nominal diameter
- Heat-treatment condition
- Finished component type
For this reason, one mechanical-property value should not be applied to every ASTM A193 grade or diameter.
ASTM A193 specifically addresses tensile and hardness properties and includes requirements associated with full-size fastener and wedge tensile testing.
Testing and Inspection
A typical ASTM A193 inspection plan may include the following examinations.
| Inspection Item | Purpose | Application |
|---|---|---|
| Chemical analysis | Confirms grade composition | Required according to material and product specification |
| Tensile testing | Verifies strength and ductility | According to grade, size and product form |
| Hardness testing | Confirms heat treatment and hardness limits | Particularly important for B7M and sour-service orders |
| Full-size fastener testing | Evaluates finished bolting performance | Where required by the standard or order |
| Dimensional inspection | Checks diameter, length and geometry | Finished bolts and studs |
| Thread inspection | Verifies pitch, class and thread dimensions | All threaded components |
| Visual inspection | Checks surface defects and workmanship | Finished products |
| Coating inspection | Confirms coating type, thickness and condition | Coated bolting |
| Nondestructive examination | Detects relevant surface or internal discontinuities | When specified |
| Positive material identification | Confirms alloy identity | When specified by the purchaser |
Optional supplementary requirements apply only when they are explicitly stated in the inquiry, purchase order or contract.
ASTM A193 Threads and Dimensions
ASTM A193 is principally a material specification, so the purchaser should separately define the required thread and dimensional standards.
Commonly referenced standards include:
| Standard | Function |
|---|---|
| ASTM A193/A193M | Bolting material, heat treatment and mechanical requirements |
| ASTM A962/A962M | Common manufacturing, testing, marking and certification requirements |
| ASTM A194/A194M | Carbon, alloy and stainless steel nuts for high-pressure or high-temperature service |
| ASME B18.31.2 | Inch-series continuous-thread, double-end and flange studs |
| ASME B1.1 | Unified inch screw threads |
| ASME B18.2.1 | Inch-series hex and heavy hex bolts |
| ASME B18.2.2 | Inch-series square, hex and heavy hex nut dimensions |
| ASTM A320/A320M | Bolting materials intended for low-temperature service |
ASTM A962 is an indispensable referenced general requirement for ASTM A193 bolting. ASTM A194 covers nuts intended for high-pressure or high-temperature service, while ASTM A320 is the relevant material specification when low-temperature bolting is required.
Common thread series include:
- UNC
- UNF
- 8UN
- Metric coarse threads
- Project-specific thread forms
The thread series, thread class, diameter and length must be clearly stated in the order.
Surface Finish and Coating Options
ASTM A193 stud bolts and bolts may be supplied with different surface finishes depending on the operating environment.
Common options include:
- Plain finish
- Black oxide
- Phosphate coating
- Electroplated zinc
- Hot-dip galvanizing
- Zinc flake coating
- PTFE coating
- Xylan coating
- Fluoropolymer coating
- Project-specific anti-corrosion coating
The coating system should be selected according to:
- Service temperature
- Atmospheric or chemical exposure
- Required coefficient of friction
- Installation torque
- Thread-fit allowance
- Coating thickness
- Project corrosion specification
A coating can change the friction coefficient and the relationship between installation torque and achieved bolt preload. The approved tightening procedure should therefore be based on the actual bolt, nut, lubricant and coating combination.
Marking and Traceability
Finished ASTM A193 bolting should be permanently identified as required by the applicable standard and purchase order.
Typical traceability information includes:
- Manufacturer identification
- ASTM grade
- Grade class when applicable
- Heat or lot number
- Product size
- Coating identification
- Inspection status
- Material certificate reference
Traceability should be maintained from the raw-material heat through heat treatment, machining, threading, coating, inspection and final packing.
Certification Documents
ASTM A193 bolting can be supplied with documentation such as:
- Mill test certificate
- Chemical composition report
- Mechanical test report
- Heat-treatment record
- Hardness report
- Dimensional inspection report
- Thread inspection report
- Coating certificate
- Positive material identification report
- Nondestructive examination report
- Third-party inspection report
- EN 10204 Type 3.1 certificate
- EN 10204 Type 3.2 certificate, when agreed
The required certificate type and inspection scope must be stated before production.
ASTM A193 Ordering Information
A complete ASTM A193 inquiry should include:
- ASTM grade and class
- Product type
- Diameter
- Overall length
- Thread series and pitch
- Thread class
- Quantity
- Matching nut grade and quantity
- Washer requirement
- Surface finish or coating
- Applicable ASTM edition
- Dimensional standard
- NACE or sour-service requirement
- Supplementary testing
- Certificate type
- Third-party inspection requirement
- Marking and packing requirements
Example Purchase Description
Stud Bolt Complete with Two Heavy Hex Nuts
- Stud Material: ASTM A193 Grade B7
- Nut Material: ASTM A194 Grade 2H
- Size: 1 in. – 8UN × 180 mm long
- Thread Class: 2A studs / 2B nuts
- Stud Dimensions: ASME B18.31.2
- Nut Dimensions: ASME B18.2.2
- Coating: PTFE fluoropolymer coating
- Certification: EN 10204 Type 3.1
- Quantity: 500 sets
ASTM A193 Applications
ASTM A193 bolting is widely specified for:
- Oil and gas pipelines
- Refineries
- Petrochemical plants
- Chemical processing facilities
- Offshore platforms
- Marine piping systems
- Power plants
- Pressure vessels
- Industrial valves
- Heat exchangers
- Boilers
- High-pressure flange connections
The final grade must be selected by the responsible engineer according to the design code, service temperature, pressure, corrosion conditions and required mechanical properties.
Frequently Asked Questions
What does ASTM A193 cover?
ASTM A193 covers alloy steel and stainless steel bolting materials and components used for high-temperature, high-pressure and other special-purpose applications.
Is ASTM A193 a bolt dimensional standard?
No. ASTM A193 primarily specifies material, heat treatment, chemical composition, mechanical properties, testing and related requirements. Bolt, stud and thread dimensions are defined by separate standards such as ASME B18.31.2 and ASME B1.1.
What is the most common ASTM A193 grade?
Grade B7 is one of the most frequently specified alloy steel grades for elevated-temperature and high-pressure flange bolting.
Which nut is used with ASTM A193 B7?
ASTM A193 B7 stud bolts are commonly supplied with ASTM A194 Grade 2H heavy hex nuts.
What is the difference between B7 and B7M?
B7 is a high-strength quenched-and-tempered alloy steel grade. B7M has more restrictive hardness controls and is commonly selected for sour-service projects or applications with specified hardness limitations.
Is ASTM A193 B7M automatically NACE compliant?
No. B7M is frequently used in sour-service applications, but final compliance must be confirmed against the specified edition of NACE MR0175/ISO 15156, the operating environment and the project requirements. (ISO)
What is the difference between B8 and B8M?
B8 is based on Type 304 stainless steel, while B8M is based on Type 316 stainless steel. B8M is generally preferred for environments requiring greater resistance to chlorides and chemical corrosion.
Can ASTM A193 stud bolts be PTFE coated?
Yes. ASTM A193 bolting can be supplied with PTFE, Xylan or other fluoropolymer coatings when permitted by the project specification. Coating thickness, friction coefficient, service temperature and thread fit should be defined in the order.
Is ASTM A193 suitable for low-temperature service?
ASTM A193 is principally intended for high-temperature, high-pressure and special-purpose applications. ASTM A320/A320M should normally be considered when low-temperature bolting and impact-toughness requirements apply.