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Flange Bolt Reference - ASME B16.5 Bolt Patterns by Pipe Size, Pressure Class & Flange Type

Look up bolt quantity, diameter, length, and torque for 150# through 2500# flanged connections

Quick-reference tool for ASME B16.5 flanged connection bolt patterns. Select pipe size (1/2" through 24") and pressure class (150, 300, 600, 900, 1500, or 2500) to see the bolt quantity, bolt diameter, bolt length, bolt circle diameter, and stud dimensions for raised face, ring-type joint, and flat face flanges. Includes recommended torque values by gasket type and bolt material grade (A193 B7, B16, L7). Cross-references ASME B16.47 for large-bore flanges 26" through 60".

Pro Tip: The most common bolt-up mistake on flanges is using the wrong bolt length. ASME PCC-1 requires stud bolts to extend at least one thread past the nut on each end but not more than 1/4 of the bolt diameter. Too-short studs do not fully engage the nut threads and risk stripping. Too-long studs make removal difficult during turnarounds and can interfere with insulation. Always verify bolt length against the actual flange thickness stack-up, including gasket and insulation flanges.

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Flange Bolt Pattern Reference
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How It Works

  1. Select Pipe Size

    Choose the nominal pipe size from 1/2" through 24" (ASME B16.5) or 26" through 60" (ASME B16.47 Series A or B). The tool covers all standard ANSI/ASME flange sizes used in process piping.

  2. Choose Pressure Class

    Select the flange pressure class: 150, 300, 600, 900, 1500, or 2500. Higher pressure classes require larger bolts, more bolts, and thicker flanges. The pressure class determines the maximum allowable working pressure at a given temperature.

  3. Review Bolt Pattern Details

    See the complete bolt pattern: number of bolt holes, bolt hole diameter, bolt circle diameter, bolt diameter, and recommended stud bolt length for the selected flange combination. Dimensions are shown for raised face (RF) and ring-type joint (RTJ) configurations.

  4. Look Up Torque Values

    Select the bolt material grade and gasket type to see recommended assembly torque values per ASME PCC-1 guidelines. Values account for bolt grade strength, gasket seating stress, and standard lubrication conditions.

Built For

  • Pipefitters identifying the correct stud bolt and nut quantities for flange make-up during turnarounds
  • Material coordinators ordering fasteners for piping fabrication and construction projects
  • Piping engineers verifying bolt patterns for flange specification sheets and isometric drawings
  • Maintenance planners building bolt kits for scheduled flange break-out and reassembly tasks
  • Inspectors verifying installed bolt sizes and quantities against ASME B16.5 requirements during audits
  • Procurement teams cross-referencing flange bolting with ASTM material specifications

Features & Capabilities

Complete B16.5 Database

Covers all ASME B16.5 flange sizes from 1/2" through 24" in pressure classes 150 through 2500. Includes bolt hole count, bolt hole diameter, bolt circle diameter, and recommended stud bolt dimensions for each size and class combination.

Large Bore B16.47 Coverage

Extends to ASME B16.47 large-bore flanges from 26" through 60" in both Series A (MSS SP-44) and Series B (API 605) configurations. These large flanges have different bolt patterns and are common in utility and pipeline applications.

Torque Cross-Reference

Links bolt pattern data to recommended torque values by bolt grade (A193 B7, B16, L7) and gasket type (spiral wound, sheet, ring gasket). Torque values follow ASME PCC-1 Appendix O guidelines for controlled bolting.

Stud Length Calculator

Calculates exact stud bolt length based on flange thickness stack-up, gasket thickness, washer configuration, and required thread protrusion past the nut per ASME PCC-1 recommendations.

Comparison

Pipe Size Class 150 Bolts Class 300 Bolts Class 600 Bolts Class 900 Bolts Class 1500 Bolts
2" 4 x 5/8" 8 x 5/8" 8 x 5/8" 8 x 3/4" 8 x 7/8"
4" 8 x 5/8" 8 x 3/4" 8 x 3/4" 8 x 1" 8 x 1-1/4"
6" 8 x 3/4" 12 x 3/4" 12 x 7/8" 12 x 1" 12 x 1-1/4"
8" 8 x 3/4" 12 x 7/8" 12 x 1" 12 x 1-1/8" 12 x 1-3/8"
12" 12 x 7/8" 16 x 1" 16 x 1-1/8" 16 x 1-1/4" 16 x 1-1/2"

Frequently Asked Questions

ASME B16.5 covers pipe flanges and flanged fittings in sizes NPS 1/2 through 24 in pressure classes 150 through 2500. ASME B16.47 covers large-diameter steel flanges in sizes NPS 26 through 60 in classes 75 through 900. B16.47 has two series: Series A (based on MSS SP-44) has more bolt holes with smaller bolts, while Series B (based on API 605) uses fewer but larger bolts. The two series are not interchangeable for a given size and class.
Stud bolt length must account for both flange thicknesses plus gasket thickness plus two heavy hex nuts plus thread protrusion past each nut. ASME PCC-1 requires a minimum of one thread exposed past the nut face and a maximum protrusion of one-quarter the bolt diameter. For a typical raised face flange-to-flange joint, the stud length equals the sum of both flange raised face thicknesses, plus gasket compressed thickness, plus two nut heights (typically 0.875 × bolt diameter each), plus two thread protrusions.
ASTM A193 Grade B7 is the standard high-strength alloy steel stud bolt material for service temperatures up to 1000°F (538°C). For temperatures above 1000°F, A193 B16 (chromium-molybdenum-vanadium alloy) maintains better strength retention. For low-temperature service below -20°F, A320 Grade L7 is specified. For corrosive environments, A193 B8 Class 1 (304 stainless) or B8M Class 1 (316 stainless) are used, though at significantly lower strength than B7. Matching nut grades: A194 Grade 2H for B7, 2HM for B16.
Raised face (RF) flanges have a raised seating surface that concentrates gasket loading. They use flat or spiral wound gaskets and are standard for ASME Class 150 and 300 in general service. Ring-type joint (RTJ) flanges have a machined groove that accepts a solid metal ring gasket (R or RX style). RTJ flanges provide superior sealing at high pressures and temperatures and are standard for Class 600 and above in hydrocarbon service. RTJ flanges require different bolt lengths than RF flanges of the same size.
A standard 6-inch ASME B16.5 Class 150 flange has 8 bolt holes on an 11.00-inch bolt circle diameter. The bolt holes are 7/8-inch diameter and accept 3/4-inch diameter stud bolts. The same 6-inch flange in Class 300 increases to 12 bolt holes with 3/4-inch studs, and in Class 600 it has 12 bolt holes with 7/8-inch studs. As pressure class increases, both the number and size of bolts increase to provide the additional clamping force needed for higher-pressure gasket seating.
ASME B16.5 specifies stud bolts (threaded rod with two heavy hex nuts) for flanged connections, and most piping codes require studs for Class 300 and above. Machine bolts (hex head with one nut) are sometimes used on Class 150 flanges in non-critical utility services, but studs are preferred because they provide more uniform thread engagement on both sides and allow the use of proper heavy hex nuts on both ends. Machine bolts are prohibited on many refineries and chemical plants regardless of pressure class.
The bolt circle diameter (BCD) is the diameter of the circle that passes through the center of all bolt holes on a flange. It is standardized by ASME B16.5 for each pipe size and pressure class. The BCD determines the moment arm for bolt clamping force acting on the gasket. A larger BCD increases the bending moment on the flange, which is why higher pressure classes have thicker flanges to resist this bending without distorting. BCD also determines whether flanges from different manufacturers are truly interchangeable.
ASME B16.5 standardizes all critical mating dimensions: bolt circle diameter, bolt hole diameter, bolt hole count and spacing, raised face diameter, raised face height, and ring groove dimensions. As long as both flanges are manufactured to B16.5 and have the same NPS, pressure class, and facing type (RF or RTJ), they will mate regardless of manufacturer. Always verify the flange marking stamp shows the correct ASME designation, material grade, and pressure class before assembly.
Disclaimer: Bolt pattern data is based on ASME B16.5 and B16.47 standards. Actual flange dimensions and bolt requirements should be verified against the current edition of the applicable ASME standard and the flange manufacturer's documentation. ToolGrit is not responsible for flange assembly integrity, bolt specification, or compliance with piping codes.

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