A193 B8M CL2 Stud Bolt: Cryogenic Impact Testing at −196°C
Most engineers are familiar with low-temperature impact testing at −20°C or −40°C. But −196°C is a different world entirely — it is the boiling point of liquid nitrogen, and it is the benchmark temperature for qualifying fasteners used in LNG (liquefied natural gas) storage and transfer systems, cryogenic process equipment, and liquid nitrogen handling facilities.
At FULLERKREG, we commission third-party cryogenic impact testing on the raw material used to manufacture our A193 B8M CL2 stud bolts. This article explains what the test is, what the results mean, and why −196°C matters.
The Product: A193 B8M CL2 Stud Bolt
| Parameter | Specification |
|---|---|
| Product Type | Stud Bolt (Double-End Stud) |
| Material Standard | ASTM A193 Grade B8M Class 2 |
| Material | AISI 316 Stainless Steel (UNS S31600) |
| Condition | Class 2 — Strain-hardened (cold-worked) for higher strength |
| Tensile Strength (Rm) | ≥862 MPa (for diameters ≤1" / 25 mm) |
| Yield Strength (Rp0.2) | ≥724 MPa |
| Elongation | ≥12% |
| Hardness | ≤321 HB |
| Key Alloying Elements | Cr 16–18%, Ni 10–14%, Mo 2–3% |
| Primary Applications | Pressure vessels, flanges, LNG equipment, cryogenic piping, chemical reactors |
Class 2 is the critical distinction from Class 1. While Class 1 is solution-annealed (softer, more ductile), Class 2 is strain-hardened by cold working — delivering significantly higher tensile and yield strength while retaining the austenitic microstructure that gives 316 stainless its outstanding cryogenic toughness.
Why −196°C? The Significance of This Test Temperature
−196°C (−20°F / 77 K) is not an arbitrary number. It is the boiling point of liquid nitrogen at atmospheric pressure, and it is used as the standard qualification temperature for materials intended for:
- LNG storage tanks and transfer lines — LNG is stored at approximately −162°C; −196°C provides a safety margin
- Liquid nitrogen systems — industrial gas production, food processing, medical cryogenics
- Liquid oxygen and liquid argon equipment — air separation plants and aerospace propulsion
- Cryogenic research facilities — superconducting magnets, particle accelerators
At these temperatures, many common engineering materials — carbon steel, low-alloy steel, most ferritic stainless steels — undergo a ductile-to-brittle transition and can fracture suddenly with little or no plastic deformation. Austenitic stainless steels like 316 (B8M) do not exhibit this transition, which is precisely why they are the material of choice for cryogenic fasteners.
A fastener that passes a −196°C impact test has demonstrated it will not become brittle at any temperature encountered in LNG or liquid nitrogen service.
The Test: ASTM E23-2024 Charpy KV8
| Test Parameter | Detail |
|---|---|
| Test Standard | ASTM E23-2024 (Standard Test Methods for Notched Bar Impact Testing) |
| Specimen Type | KV8 — Charpy V-notch, 8 mm sub-size specimen |
| Test Temperature | −196°C (liquid nitrogen temperature) |
| Specimen Source | Raw material test bar (machined from the same heat as the stud bolts) |
| Number of Specimens | 3 |
| Testing Laboratory | China Components Test (CCT) — Report No. 2025554910 |
The KV8 sub-size specimen (8 mm × 10 mm cross-section) is used when the material section is too small to machine a full-size 10 mm × 10 mm Charpy specimen. This is common for stud bolt raw material bars. Results from sub-size specimens are directly comparable when the same specimen geometry is consistently used and reported.
The specimens are cooled to −196°C by immersion in liquid nitrogen, then transferred to the impact machine and struck within a controlled time window to ensure the test temperature is maintained at the moment of fracture.
Test Report: Results at −196°C
The following results are recorded in third-party test report No. 2025554910 (Page 2/2), issued by China Components Test (CCT), for the raw material test bar of our A193 B8M CL2 stud bolts:
| Test Item | Test Method | Requirement | Result (3 specimens, J) | Conclusion |
|---|---|---|---|---|
| Impact Absorbed Energy KV8 at −196°C (J) | ASTM E23-2024 | Recorded (no minimum specified for raw material bar) | 177 / 164 / 194 | Recorded — for material qualification |
Note: This test was performed on a raw material test bar machined from the same heat as the stud bolts. The results are recorded as material qualification data. No minimum requirement is specified in the report because the test was commissioned as a characterization test rather than a pass/fail acceptance test against a specific product standard minimum.
Interpreting the Results
| Metric | Value |
|---|---|
| Test temperature | −196°C (liquid nitrogen) |
| Specimen 1 | 177 J |
| Specimen 2 | 164 J |
| Specimen 3 | 194 J |
| Average absorbed energy | 178 J |
| Minimum individual result | 164 J |
| Result consistency (max − min) | 30 J (excellent consistency) |
These results are exceptional. To put them in context:
- The ISO 898-1 minimum for a standard carbon steel fastener at −20°C is just 27 J. Our B8M material absorbs 164–194 J at −196°C — a temperature 176°C colder.
- The three specimens show excellent consistency (range of only 30 J), confirming uniform material quality throughout the heat.
- The high absorbed energy values confirm that the austenitic microstructure of 316 stainless steel is fully retained at liquid nitrogen temperature — no brittle fracture, no ductile-to-brittle transition.
In practical terms: a stud bolt made from this material will deform plastically rather than fracture suddenly even if subjected to an impact load at −196°C. This is the fundamental safety characteristic required for LNG and cryogenic service.
Why Austenitic Stainless Steel Stays Tough at −196°C
The secret lies in the crystal structure. Austenitic stainless steels (including 316 / B8M) have a face-centered cubic (FCC) crystal lattice. FCC metals have multiple slip systems that allow plastic deformation at any temperature — they do not undergo the ductile-to-brittle transition that occurs in body-centered cubic (BCC) metals like carbon steel and ferritic stainless steels.
| Material Type | Crystal Structure | Ductile-to-Brittle Transition | Suitable for −196°C? |
|---|---|---|---|
| Carbon steel (e.g., A307) | BCC | Yes — typically −20°C to −60°C | No |
| Ferritic stainless (e.g., 430) | BCC | Yes | No |
| Martensitic stainless (e.g., 410) | BCT | Yes | No |
| Austenitic stainless (316 / B8M) | FCC | No | Yes |
| Nickel alloys (Inconel, Monel) | FCC | No | Yes |
| Titanium alloys (Grade 2, Grade 5) | HCP / mixed | Limited | Grade-dependent |
FULLERKREG Supply Capabilities
FULLERKREG supplies A193 B8M CL2 stud bolts with full material traceability and third-party test documentation for cryogenic and LNG applications:
- Cryogenic impact test reports — ASTM E23, −196°C, third-party accredited laboratory
- Material Test Certificates (MTC) — EN 10204 3.1 / 3.2, chemical composition and mechanical properties
- ASTM A193 B8M CL2 compliance — full mechanical property verification per ASTM A193
- Custom stud bolt dimensions — non-standard lengths, thread forms, and end configurations
- Bulk wholesale pricing — OEM and MRO procurement with competitive lead times
- Global shipping — from our manufacturing base in China to customers worldwide
Specifying A193 B8M CL2 stud bolts for an LNG, cryogenic, or pressure vessel application? Contact FULLERKREG — we will provide full documentation including cryogenic impact test data with your order.
FULLERKREG — Precision Fasteners. Global Standards. Reliable Supply.