ASTM A320 vs ASTM A193: Low-Temperature vs High-Temperature Bolting
Two ASTM bolting specifications, two service-temperature regimes
ASTM A320 and ASTM A193 are companion bolting specifications that share much of the same chemistry but target different service-temperature regimes. ASTM A320 / A320M covers low-temperature service and mandates Charpy V-notch impact testing. ASTM A193 / A193M covers high-temperature pressure service and does not require Charpy testing. Engineers selecting between the two must identify whether minimum metal temperature or maximum service temperature drives the design.
Scope difference
- ASTM A320: bolting for pressure vessels, valves, flanges, and fittings at low service temperatures. Charpy V-notch impact testing mandatory.
- ASTM A193: bolting for high-temperature or high-pressure service. No Charpy requirement; tensile and yield tested at room temperature.
Grade overlap (same chemistry, different test)
Several grades have identical chemistry across the two standards:
- A193 Grade B7 (4140 / 4142 Q&T) vs A320 Grade L7 (same chemistry, plus Charpy at -150°F)
- A193 Grade B7M vs A320 Grade L7M (sour-service variant, plus Charpy)
- A193 Grade B8 (304 stainless) vs A320 Grade B8
- A193 Grade B8M (316 stainless) vs A320 Grade B8M
- A193 Grade B8C (347 stainless) vs A320 Grade B8C
- A193 Grade B8T (321 stainless) vs A320 Grade B8T
When to specify A320 instead of A193
Specify ASTM A320 when the minimum design metal temperature (MDMT) drops below the A193 service window or when project specifications mandate notch toughness verification. Typical A320 applications: LNG plants, cryogenic pipelines, North Sea offshore platforms, industrial refrigeration, and pressure equipment with sub-zero MDMT. Conversely, A193 is the correct selection for steam service, refinery towers, and high-temperature pressure vessels where MDMT stays above the A320 threshold.