AISI 305 low-work-hardening austenitic stainless steel · Solution-treated (Class 1) or strain-hardened (Class 2)
ASTM A320 Grade B8P is an austenitic stainless steel bolting grade specified per ASTM A320/A320M-21 for low-temperature service. Assigned UNS number S30500. Manufactured from AISI 305 low-work-hardening austenitic stainless steel. The grade is supplied in Class 1 (solution-treated) or Class 2 (strain-hardened) condition, with Class 2 offering higher tensile strength through controlled cold work. Grade B8P is the cold-heading variant of 304 stainless, with reduced work-hardening for severe cold-forming. Grade B8P is intended for stud bolts and hex bolts in pressure vessels, valves, flanges, and fittings exposed to corrosive or low-temperature environments. Grade B8P is equivalent to ASME SA-320 Grade B8P in Section II of the ASME Boiler and Pressure Vessel Code.
| Grade Symbol | UNS Designation | C, max | Mn, max | P, max | S, max | Si, max | Ni | Cr | |
|---|---|---|---|---|---|---|---|---|---|
| ASTM A320 B8P | S30500 | Range,% | 0.12 | 2.00 | 0.045 | 0.030, max | 1.00 | 11- 13.0 | 17.0- 19.0 |
| Product Variation, % Over or Under | 0.01 over | 0.04 over | 0.010 over | 0.005 over | 0.05 over | 0.15 | 0.20 | ||
| Grade and Class | Diameter, in. [mm] | Heat Treatment | Tensile Strength, min, ksi [MPa] | Yield Strength, min, ksi [MPa] (0.2 % offset) | Elongation in 2 in. or 50 mm, min, % | Reduction of Area, min, % | Hardness, max |
|---|---|---|---|---|---|---|---|
| ASTM A320 B8P : Class 1 | All diameters | carbide solution treated | 75 [515] | 30 [205] | 30 | 50 | 223 HBWDor 96 HRB |
| ASTM A320 B8P : Class 2 | 3/4 [20] and under | carbide solution treated and strain hardened | 125 [860] | 100 [690] | 12 | 35 | 321 HBW or 35 HRC |
| over 3/4 to 1 [20 to 25], incl | 115 [795] | 80 [550] | 15 | 30 | 321 HBW or 35 HRC | ||
| over 1 to 11/4 [25 to 32], incl | 105 [725] | 65 [450] | 20 | 35 | 321 HBW or 35 HRC | ||
| over 11/4 to 11/2 [32 to 40], inclA | 100 [690] | 50 [345] | 28 | 45 | 321 HBW or 35 HRC |
For low-temperature service consistency, ASTM A320 Grade B8P stud bolts are paired with ASTM A194 Grade 8 series austenitic heavy hex nuts (A320 10.2 lists Grades 8, 8C, 8T, 8F, 8M, 8LN, and 8MLN) and austenitic steel washers as agreed between manufacturer and purchaser (A320 10.5). ASTM F436 hardened steel washers are for ferritic bolting (A320 10.4). TorqBolt supplies kit-matched A320 B8P + A194 + austenitic washer sets with a single EN 10204 3.1 or 3.2 certificate covering all three components.
TorqBolt’s ASTM A320 Grade B8P stud bolt production route is qualified to NORSOK M-650 for North Sea oil & gas offshore service. Each manufacturing record links heat number, melt analysis, heat-treatment batch, mechanical test, dimensional inspection, surface treatment, and dispatch. Standard certification is EN 10204 Type 3.1 (inspection certificate with test results, validated by the manufacturer’s authorized inspection representative); Type 3.2 third-party witnessed by Lloyd’s Register, DNV, BV, ABS, or TUV is available on request. The qualification packet covers ASME SA-320 B8P equivalence, NACE MR0175 / ISO 15156-3 sour-service compliance (where applicable), and PED 2014/68/EU for European pressure-equipment buyers.
