ASME B16.5 Flanges Guide: ANSI B16.5 Dimensions, Classes and Buying Checks

ASME B16.5 is one of the most important standards used when engineers, EPC buyers and maintenance teams order metallic pipe flanges. You may also see older project documents write ANSI B16.5, ASME B16, ASME 16.5 B or simply 16.5 B. In most purchasing conversations, these terms point to the same family of ASME B16.5 flanges used in class-rated piping systems.

This guide explains what ASME B16 5 flanges mean in practical work, what information the standard controls, and how to avoid ordering mistakes when buying ASME B16.5 flanges for industrial piping.

What Does ASME B16.5 Mean?

ASME B16.5 is a standard for pipe flanges and flanged fittings. It gives a common language for nominal pipe size, pressure class, flange dimensions, bolt drilling, facing type, tolerances, material rating groups and marking. This makes flanges from different qualified manufacturers easier to match during installation.

When a drawing says ANSI B16.5, the project may be using old wording. Modern documents normally use ASME B16.5, but many buyers still search for ANSI B16.5 because older standards and plant records used ANSI language for years.

ASME B16.5 Size and Class Range

ASME B16.5 applies to common metallic flanges and flanged fittings in the usual NPS 1/2 through NPS 24 range. For larger diameter steel flanges, many projects use ASME B16.47 instead. This is why size confirmation is one of the first steps before quoting any ASME B16.5 flanges.

The standard uses pressure classes such as Class 150, 300, 400, 600, 900, 1500 and 2500. These class numbers are not direct working pressure values for every service. The allowable pressure depends on temperature, material group and the selected rating table.

What ASME B16.5 Controls

A flange standard is useful because it controls the interface between parts. For ASME B16 5 flanges, the most important controlled items include:

• Nominal pipe size and pressure class.
• Outside diameter, thickness, bore and hub dimensions.
• Bolt circle diameter, bolt hole quantity and bolt hole size.
• Facing type such as raised face, flat face or ring type joint.
• Dimensional tolerances for predictable fit-up.
• Pressure-temperature ratings by material group.
• Marking requirements for identification and traceability.

Common Flange Types Under ASME B16.5

Many common flange styles are ordered under ASME B16.5. These include weld neck flanges, slip on flanges, blind flanges, socket weld flanges, threaded flanges and lap joint flanges. Each type solves a different installation or service problem.

Flange Type	Typical Use	Key Check
Weld neck flange	High pressure, high temperature, cyclic or critical service	Pipe schedule, bevel and welding procedure
Slip on flange	Utility and moderate service where quick fit-up matters	Bore, pipe OD and fillet weld requirement
Blind flange	Closing pipe ends, nozzles and inspection openings	Pressure class, face type and bolt set
Socket weld flange	Small-bore high-pressure piping	Socket bore, gap and weld quality
Threaded flange	Low-pressure or non-welded connections where allowed	Thread type and sealing method
Lap joint flange	Easy alignment and frequent disassembly with stub ends	Stub end compatibility and backing flange fit

ASME B16.5 vs ANSI B16.5

Buyers often ask whether ASME B16.5 and ANSI B16.5 are different. In many real-world RFQs, ANSI B16.5 is legacy wording and ASME B16.5 is the current way most suppliers describe the standard. The safe approach is to follow the exact project specification and confirm the required edition, class, size and face type in writing.

If an old plant drawing uses ANSI B16.5 while a new project specification uses ASME B16.5, do not assume everything is correct automatically. Confirm dimensions, drilling and gasket face before manufacturing replacement flanges.

Pressure Class Is Not the Same as Working Pressure

A common mistake is treating Class 150 or Class 300 as a fixed pressure number. The flange class is a rating category. The actual allowable pressure changes with material group and operating temperature. For hot service, the pressure capability can be lower than the ambient reference value.

When ordering ASME B16 5 flanges for steam, chemical, oil and gas or power generation service, send the design pressure, design temperature, fluid and material grade. This allows the engineering team to verify the correct pressure-temperature rating.

Face Type and Gasket Matching

ASME B16.5 flanges may use raised face, flat face or ring type joint facing depending on service and class. The face type must match the gasket and mating flange. A raised face flange should not be casually bolted to a flat face component without engineering review, especially when the mating part is cast iron or another brittle material.

For export orders, face type should appear clearly on the purchase order, drawing and packing list. Short phrases such as “B16.5 flange” are not enough because two flanges with the same size and class can still have different sealing faces.

Material Selection and Marking

The standard organizes materials by rating groups, but buyers still need to specify the actual material grade. Common choices include ASTM A105 carbon steel, ASTM A350 low-temperature carbon steel, ASTM A182 stainless steel and alloy grades for higher temperature or corrosion service.

Marking is also important. A compliant flange should be traceable by size, class, material grade, standard designation, manufacturer marking and heat or lot identification when required. For critical service, match the flange marking with the material test certificate before installation.

ASME B16.5 and ASME B16.47

ASME B16 is a family of standards, and ASME B16.5 does not cover every size. Large diameter steel flanges commonly move to ASME B16.47 Series A or Series B. EN and DIN systems use DN and PN terminology with different drilling patterns, so they should not be mixed with ASME class flanges by pressure comparison alone.

If your project has both ASME and metric PN equipment, plan adapter flanges or transition spools early. Bolt holes, gasket seating and face dimensions must be checked before parts are machined.

Purchasing Checklist for ASME B16.5 Flanges

To order correctly, send more than the phrase asme 16.5 b or 16.5 b. A clear RFQ should include standard, edition if specified, flange type, NPS size, pressure class, material grade, pipe schedule, face type, quantity, inspection requirement and delivery destination.

• Confirm ASME B16.5 or another governing standard.
• Confirm NPS size and pressure class.
• Confirm flange type and pipe schedule or bore.
• Confirm RF, FF or RTJ face type.
• Confirm material grade and certificate requirement.
• Confirm bolting, gasket and inspection needs for the service.

FAQ About ASME B16.5 Flanges

What are ASME B16 5 flanges?

ASME B16 5 flanges are metallic pipe flanges manufactured to ASME B16.5 dimensions, pressure classes, face types, tolerances and marking rules within the standard scope.

Is ANSI B16.5 the same as ASME B16.5?

In many older drawings and buyer requests, ANSI B16.5 is used as legacy wording for the same general flange standard family. Modern specifications normally use ASME B16.5, so confirm the required project edition before ordering.

What size range does ASME B16.5 cover?

It is commonly used for NPS 1/2 through NPS 24 metallic pipe flanges and flanged fittings. Larger steel flanges are typically specified under ASME B16.47 or another project standard.

What should be checked before buying ASME B16.5 flanges?

Check flange type, size, class, material, pipe schedule, face type, gasket, bolting, marking, certificates and the operating temperature used for pressure rating verification.

Need ASME B16.5 or ANSI B16.5 Flanges?

Songhai Flange supplies ASME B16.5 flanges, ANSI B16.5 replacement flanges, weld neck flanges, slip on flanges, blind flanges, socket weld flanges, threaded flanges and custom flange products for industrial piping, oil and gas, chemical, power, water treatment and OEM projects. If you need help with drawings, material selection, machining, inspection or export packing, our team can support your project.