ASME B16.5 Class 400 blind flanges serve a specific operational niche: isolating pipe ends, valve terminations, and pressure vessel nozzles rated for intermediate working pressures up to 980 psi (67.6 bar) at ambient temperatures. HT PIPE supply all different types and scales of flanges. Please feel free to contact us for further product information and pricing.
Key Design Factors & Procurement Specifications
1. Material Selection Standards
Blind flanges in Class 400 service bear full system hydrostatic pressure across their un-bored center area. Material grade selection must align with ASTM piping specifications:
ASTM A105: Standard forged carbon steel for ambient and high-temperature service.
ASTM A350 LF2: Low-temperature carbon steel common in North American cold-weather installations and cryogenic gas processing.
ASTM A182 F316/316L or F304/304L: Stainless steel grades specified for corrosive refining, chemical handling, or offshore environments.
2. Facing Types: RF vs. RTJ
Raised Face (RF): Features a 0.25-inch (6.4 mm) raised section with smooth or serrated concentric finishes (typically 125–250 AARH) for spiral wound gaskets.
Ring-Type Joint (RTJ): Features a precision-machined metallic groove designed for metallic ring gaskets (e.g., Style R or RX). RTJ facings are widely preferred on high-pressure Gulf Coast offshore platforms and high-temperature refinery loops due to superior seal integrity under cyclic loading.
Pressure-Temperature Working Limits
A common misconception in piping design is treating "Class 400" as a fixed working pressure of 400 psi. In reality, working pressure limits fluctuate significantly based on operating temperature and material selection per ASME B16.5 Table 2 ratings.
ASTM A105 / A350 LF2 (Carbon Steel - Group 1.1)
-20°F to 100°F (-29°C to 38°C): 980 psig (67.6 bar)
200°F (93°C): 925 psig (63.8 bar)
400°F (204°C): 825 psig (56.9 bar)
600°F (315°C): 720 psig (49.6 bar)
800°F (426°C): 510 psig (35.2 bar)
ASTM A182 F316/F316L (Stainless Steel - Group 2.2)
-20°F to 100°F (-29°C to 38°C): 960 psig (66.2 bar)
200°F (93°C): 815 psig (56.2 bar)
400°F (204°C): 695 psig (47.9 bar)
600°F (315°C): 605 psig (41.7 bar)
800°F (426°C): 550 psig (37.9 bar)
Dimensional Tolerances (ASME B16.5 Clause 7)
Quality inspection protocols rely on enforcing standard machining tolerances:
Outside Diameter (O):
NPS 24 and smaller: +/- 0.06 in (+/- 1.6 mm)
Flange Thickness (T):
NPS 18 and smaller: +0.12 in / -0.00 in (+3.0 mm / -0.0 mm)
NPS 20 and larger: +0.20 in / -0.00 in (+5.0 mm / -0.0 mm)
Bolt Circle Diameter (C): +/- 0.06 in (+/- 1.6 mm)
Bolt Hole Center Offset: Maximum offset of 0.03 in (0.8 mm) between adjacent hole centers.
Raised Face Diameter (R): +/- 0.04 in (+/- 1.0 mm)
ASME B16.5 Class 400 Blind Flange Dimensions
