STD-TB-BUL-5368 Stud Bolt Specification: Technical Guide for Piping Flange Bolting
What Is STD-TB-BUL-5368?
STD-TB-BUL-5368 is an engineering specification originally issued by Snamprogetti for stud bolts, nuts, and washers used in piping flange connections.
It provides technical guidance on bolting configurations, thread designations, dimensional requirements, length tolerances, material identification, and inspection.
Unlike ASTM A193 or ASME B1.1, STD-TB-BUL-5368 is a company engineering specification rather than a general international product standard.
It may be referenced in procurement documents for oil and gas facilities, refineries, petrochemical plants, and other industrial piping projects.
Important: The currently applicable revision has not been independently verified. The project-approved specification and purchase order should always govern manufacturing and inspection.
1. Stud Bolt Assembly Configuration
Piping flange bolting assemblies generally consist of a fully threaded stud bolt and heavy hex nuts.
The referenced STD-TB-BUL-5368 revision addresses two assembly configurations:
| Assembly Type | Components |
|---|---|
| Standard Assembly | 1 Stud Bolt + 2 Heavy Hex Nuts |
| Assembly with Washers | 1 Stud Bolt + 2 Heavy Hex Nuts + 2 Washers |
The appropriate configuration depends on the piping design and purchase order.
Washers should not be automatically included unless specified in the procurement documents.
For engineering applications, the following details should be reviewed together:
- Stud bolt nominal diameter and length
- Thread series and tolerance class
- Stud bolt and nut material grades
- Washer requirements
- Surface treatment or protective coating
- Inspection and certification requirements
2. Thread Requirements: UNC and 8UN
Thread compatibility is a critical factor in stud bolt assembly selection.
The historical STD-TB-BUL-5368 revision refers to ASME B1.1 for unified inch screw threads.
It identifies UNC threads for diameters up to and including 1 inch, and 8UN threads for larger diameters.
| Diameter Range | Stud Bolt Thread | Nut Thread |
|---|---|---|
| Up to and including 1″ | UNC, Class 2A | UNC, Class 2B |
| Above 1″ | 8UN, Class 2A | 8UN, Class 2B |
Understanding UNC and 8UN Threads
UNC (Unified National Coarse) is a standardized coarse-thread series.
8UN is a unified constant-pitch thread series with eight threads per inch.
The distinction becomes particularly important for larger-diameter studs used in high-pressure flange connections.
For example:
- 3/4″ stud bolt: 3/4″-10 UNC
- 1″ stud bolt: 1″-8 UNC
- 1-1/8″ stud bolt: 1-1/8″-8UN
- 1-1/2″ stud bolt: 1-1/2″-8UN
These examples illustrate the specified thread series. The complete thread designation, including tolerance class, should be confirmed against the applicable engineering documents.
Engineering note: Thread pitch alone does not establish complete interchangeability. The thread series, class of fit, manufacturing tolerances, and applicable coating must also be considered.
3. Stud Bolt Dimensions and Length Tolerances
Stud bolt dimensions must be consistent with the flange design, applicable engineering standards, and procurement requirements.
The historical STD-TB-BUL-5368 revision refers to ASME B18.2.2 for heavy hex nut dimensions.
Stud bolt length is normally established through the purchase order.
Length Tolerance Requirements
The December 2002 revision identifies the following nominal length tolerance ranges:
| Nominal Stud Length | Length Tolerance |
|---|---|
| Up to 300 mm | +1.6 / −0 mm |
| Above 300 mm to 460 mm | +3.2 / −0 mm |
| Above 460 mm | +6.4 / −0 mm |
These values are provided for technical reference to the identified historical revision and should not be used as substitutes for the controlled project specification.
Why Stud Bolt Length Measurement Matters
Different engineering specifications may define stud bolt length differently.
Some dimensional conventions include the overall end-to-end length, while others define the working length between specified thread reference points.
The historical STD-TB-BUL-5368 document uses a measurement convention that excludes designated end-point dimensions.
An incorrect interpretation can result in supplied bolts that do not meet the dimensional requirements, even when the nominal length appears correct.
Before manufacturing, the supplier should confirm the measurement convention and any specific requirements for end-point finishing.
4. Stud Bolt and Nut Material Selection
STD-TB-BUL-5368 should not be interpreted as specifying a single material grade for every bolting application.
Materials must be selected according to the applicable piping material specification, operating conditions, and purchase order.
Examples of common industrial bolting material combinations include:
| Stud Bolt Material | Nut Material | Typical Application Consideration |
|---|---|---|
| ASTM A193 B7 | ASTM A194 2H | General alloy-steel pressure bolting |
| ASTM A193 B7M | ASTM A194 2HM | Applications requiring controlled hardness and specific material properties |
| ASTM A320 L7 | ASTM A194 7 | Low-temperature bolting applications |
| ASTM A193 B8M | ASTM A194 8M | Stainless steel bolting where corrosion resistance is required |
These are illustrative material combinations, not a list of materials automatically approved by STD-TB-BUL-5368.
Actual material selection must consider design temperature, pressure, corrosion conditions, mechanical properties, and any project-specific restrictions.
For sour-service applications, compliance with NACE MR0175 / ISO 15156, where applicable, must be separately assessed. Material grade identification alone does not establish sour-service suitability.
5. Inspection and Quality Control
Inspection is an important part of industrial stud bolt manufacturing, especially for bolting assemblies used in critical piping systems.
The publicly available 2002 revision includes requirements relating to surface examination, product identification, and supporting quality documentation.
Surface Examination
The historical document references magnetic particle and liquid penetrant examination methods.
The purpose of these examinations is to identify relevant surface discontinuities that may affect component integrity.
Magnetic Particle Testing (MT) is generally applicable to suitable ferromagnetic materials.
Liquid Penetrant Testing (PT) can be used to identify surface-breaking discontinuities on suitable nonporous materials.
The historical document includes references to ASTM E109, ASTM E138, and ASTM E165.
Some of these references are now obsolete or withdrawn. For current procurement, the applicable inspection procedures and editions should be confirmed with the purchaser rather than substituted automatically.
Current industry references may include ASTM E709 for magnetic particle testing and ASTM E165/E165M for liquid penetrant testing, subject to project approval.
Inspection Sampling
The historical revision also contains sampling requirements for surface examination, including a defined percentage of the supply lot and a minimum specimen quantity.
The sampling method, acceptance criteria, and inspection extent should be verified against the applicable project specification.
For critical-service bolting, additional inspection requirements may be established by the purchaser.
6. Material Traceability and Certification
Traceability helps ensure that the delivered stud bolts and nuts correspond to the specified material grades and manufacturing records.
Typical procurement documentation may include:
- Material Test Certificates (MTC)
- Chemical composition results
- Mechanical test results
- Dimensional inspection reports
- Surface examination reports, where required
- Heat-number and batch traceability records
- Coating inspection reports, where applicable
The documentation scope should be agreed before manufacturing.
Where EN 10204 Type 3.1 certification is required, it should be explicitly stated in the purchase order.
STD-TB-BUL-5368 should not be interpreted as automatically requiring EN 10204 Type 3.1 certification for every supply.
7. Coating and Surface Protection
Depending on the operating environment, stud bolt assemblies may require additional corrosion protection.
Common options in industrial bolting procurement include:
| Coating Option | Engineering Consideration |
|---|---|
| Uncoated / As Manufactured | Material compatibility and corrosion environment |
| PTFE-Based Coating | Corrosion protection and friction characteristics |
| Xylan-Type Fluoropolymer Coating | Controlled friction and corrosion protection, depending on the specified system |
| Hot-Dip Galvanizing | Zinc coating requirements and post-coating thread compatibility |
These are general industrial coating options and are not mandatory coating requirements of STD-TB-BUL-5368.
Special attention should be given to thread fit after coating and the relationship between coating friction properties and the specified tightening procedure.
Coating acceptance criteria, thickness, qualification, and testing should be separately defined in the purchase specification.
8. Relationship Between STD-TB-BUL-5368 and ASTM / ASME Standards
Different standards address different aspects of industrial bolting.
| Standard / Specification | Primary Function |
|---|---|
| STD-TB-BUL-5368 | Project or company engineering requirements for flange bolting assemblies |
| ASTM A193/A193M | Material requirements for specified pressure bolting |
| ASTM A194/A194M | Material requirements for nuts used in designated service conditions |
| ASME B1.1 | Unified inch screw thread requirements |
| ASME B18.2.2 | Nut dimensional requirements |
| ASTM E709 | Magnetic particle testing guidance |
| ASTM E165/E165M | Liquid penetrant testing procedures |
Compliance with ASTM A193 and ASTM A194 does not automatically establish compliance with STD-TB-BUL-5368.
Similarly, meeting the thread requirements of ASME B1.1 does not by itself confirm full compliance with the project bolting specification.
Material requirements, dimensions, inspection, identification, and documentation must be reviewed collectively.
9. How to Specify STD-TB-BUL-5368 Stud Bolts in an RFQ
A clear purchase description reduces technical ambiguity and helps manufacturers provide comparable quotations.
Example Procurement Description
Product: Fully Threaded Stud Bolt with 2 Heavy Hex Nuts
Diameter: 1-1/2″
Nominal Length: 300 mm
Thread: 1-1/2″-8UN
Stud Bolt Material: ASTM A193 Grade B7M
Nut Material: ASTM A194 Grade 2HM
Referenced Specification: STD-TB-BUL-5368
Applicable Revision: To be confirmed by purchaser
Coating: As specified in the purchase order
Inspection and Certification: As specified in the approved project documentation
This example is illustrative and does not establish a complete manufacturing specification.
10. Frequently Asked Questions
Is STD-TB-BUL-5368 an ASTM standard?
No. It is a Snamprogetti company engineering specification that references selected ASME and ASTM standards.
What products does STD-TB-BUL-5368 cover?
The historical revision addresses stud bolts, heavy hex nuts, and washers for industrial piping flange bolting assemblies.
What is the difference between UNC and 8UN threads?
UNC is a coarse-thread series, while 8UN is a constant-pitch series with eight threads per inch. The historical specification uses UNC through 1 inch and 8UN for larger stud diameters.
Does STD-TB-BUL-5368 require ASTM A193 B7 material?
Not for all applications. The required stud bolt and nut grades depend on the purchase order and project piping material specification.
Does STD-TB-BUL-5368 require magnetic particle testing?
The publicly available 2002 revision contains surface examination requirements and references magnetic particle and liquid penetrant examination methods. The applicable inspection procedure and acceptance criteria must be established from the project’s controlled specification.
Are PTFE or Xylan coatings required?
No universal coating requirement should be assumed from the STD-TB-BUL-5368 designation alone. Protective coatings should be expressly specified where needed.
Can ASTM A193 B7 stud bolts be supplied as STD-TB-BUL-5368 compliant?
Potentially, provided the complete assembly meets the applicable material, thread, dimensional, inspection, marking, and project-specific requirements. Material compliance alone is not sufficient.
Is STD-TB-BUL-5368 still valid?
A December 2002 Revision 01 document is publicly accessible, but its current controlled status has not been verified. The purchaser should identify the applicable revision.
Technical References and Disclaimer
This article is an independent engineering and procurement guide discussing the historical STD-TB-BUL-5368 specification and related industrial bolting practices.
Reference documents include:
- Snamprogetti STD-TB-BUL-5368, Revision 01, December 2002
- ASME B1.1 – Unified Inch Screw Threads
- ASME B18.2.2 – Nuts for General Applications
- ASTM A193/A193M – Alloy-Steel and Stainless Steel Bolting
- ASTM A194/A194M – Carbon, Alloy and Stainless Steel Nuts
- ASTM E709 – Magnetic Particle Testing
- ASTM E165/E165M – Liquid Penetrant Testing
This article is not an official publication, authorized reproduction, or certified interpretation of STD-TB-BUL-5368. It is not affiliated with or endorsed by Snamprogetti or Saipem.
All rights in the original specification remain with the applicable rights holders.
For manufacturing, quality inspection, and contractual compliance, users must refer to the authorized project specification, applicable standards, and approved purchase order.
