Procurement standard brief
ASME B16.5: Pipe Flanges and Flanged Fittings
Use ASME B16.5 to define the covered flange or flanged-fitting dimensional and rating system, then pair it with the selected material specification and piping-class requirements. A usable line item needs NPS, pressure class, flange type, facing, bore, wall or schedule interface, material standard and grade, dimensional options, marking, testing, and documentation. B16.5 does not turn an unspecified stainless forging into a complete flange purchase, select the alloy for the fluid, or approve the joint for a project. The piping designer must coordinate pipe, flange, gasket, bolting, temperature, corrosion allowance, fabrication, and code acceptance.
- Use this guide for
- Piping-class definition and flange RFQ preparation
- Relevant to
- Piping engineers, EPC buyers, valve and equipment purchasers, fabricators, and flange distributors
Contract responsibility
Scope and Explicit Exclusions
What this material standard controls
Flange geometry and class system
B16.5 provides the framework for covered flange types, nominal pipe sizes, pressure classes, dimensions, facings, tolerances, marking, and associated rating information. The buyer must select the exact NPS, class, type, facing, and bore arrangement.
Joint interface
The standard coordinates the flange connection with bolting and gasket interfaces, but the piping class selects compatible materials and components. Facing finish, gasket type, bolt specification, assembly procedure, and service restrictions still need project control.
Testing and marking framework
The standard includes requirements relevant to covered products and identification. Material certification, supplementary examination, PMI, heat treatment records, and project marking must be added through the material standard and purchase order.
What it does not control alone
- ASME B16.5 is not the stainless material specification; forged stainless flanges commonly require a separately named specification such as ASTM A182/A182M and an exact grade.
- It does not select a pressure class from fluid, design pressure, temperature, corrosion, transient, external load, gasket, or bolting conditions, and it does not replace the governing piping code.
- It does not define fabrication weld procedures, joint assembly, bolt loading, system examination, cleaning, passivation, pressure testing, or final plant acceptance.
Specification stack
Related Standards and Responsibility Chain
| Document | Procurement role | Boundary |
|---|---|---|
| ASME B16.5 | Defines the covered flange and flanged-fitting geometry, pressure-class framework, facings, tolerances, marking, testing provisions, and joint interfaces. | It requires a separately selected material and does not choose a class or alloy for the actual service. |
| ASTM A182/A182M or specified material standard | Defines the forged or rolled stainless flange material, grade, heat treatment, mechanical tests, examination options, marking, and certification. | Material conformity does not establish B16.5 dimensions or a piping-class rating by itself. |
| Pipe, fitting, bolting, and gasket specifications | Provide the mating pipe dimensions and material, connected fitting route, fastener materials, and sealing element required for the joint. | Components must be selected as one compatible assembly rather than by independent trade descriptions. |
| Governing piping code and project piping class | Control design conditions, allowable combinations, corrosion allowance, class selection, welding, examination, assembly, testing, and approval. | The project authority decides whether the completed flange joint is acceptable for service. |
Line-item completeness
How to Order to This Standard
| Field | What to state | Why it matters |
|---|---|---|
| Standard and revision | State ASME B16.5 and the contract revision, plus the governing piping code, piping-class document, and flange datasheet where applicable. | Dimensional and rating clauses must match the project design basis. |
| NPS and pressure class | Give nominal pipe size and selected class exactly as approved by the piping class. | Size and class drive dimensions, bolting pattern, thickness, facing, and compatibility. |
| Flange type | Identify weld neck, slip-on, blind, socket-weld, threaded, lap-joint, or covered flanged fitting and any long-weld-neck or drawing-specific configuration. | Type changes bore, attachment, welding, geometry, and inspection. |
| Facing and finish | State raised face, flat face, ring-type joint, or other permitted facing; include facing finish or project criterion and protective requirements. | Gasket sealing depends on a coordinated facing, surface, gasket, and assembly procedure. |
| Bore and pipe interface | Define bore, mating pipe OD and wall or schedule, hub end preparation, weld detail, and any corrosion allowance or transition. | A class and NPS do not uniquely define the weld-neck bore or fit to the selected pipe. |
| Material | Name the material specification, exact stainless grade, product form, heat treatment, and any supplementary restriction. | B16.5 alone does not order stainless chemistry, properties, or forging quality. |
| Testing and documents | Specify certificate, heat traceability, PMI, NDE, hardness, impact or corrosion testing where required, dimensional report, and witness points. | Project evidence must be included before forging, machining, and allocation. |
| Quantity and delivery | List piece count, matching components if included, marking, coating or passivation boundary, protectors, packing, document index, and release terms. | Identity and machined sealing faces need protection through transport and site receipt. |
Copy structure, replace values
Purchase Description Example
Pre-award review
Ordering Mistakes and Corrections
| Mistake | Likely consequence | Correction |
|---|---|---|
| Ordering only "B16.5 316L flange". | NPS, class, flange type, facing, bore, material specification, tests, documents, and mating components remain undefined. | Issue the complete piping-class designation and purchase line with material standard, grade, geometry, examination, marking, and packing. |
| Treating pressure class as a stand-alone allowable pressure. | The rating basis can be misapplied without the material group, temperature, piping code, gasket, bolting, loads, corrosion, and project restrictions. | Have the piping designer select the class and joint using the contract edition, design conditions, material group, and governing code. |
| Assuming every NPS and class flange has one bore. | The flange may not match the selected pipe wall, schedule, corrosion allowance, or weld transition. | State the mating pipe OD and wall, required bore, hub and end preparation, and controlling detail. |
| Specifying a facing without the gasket and bolting system. | A dimensionally correct flange can still form an incompatible or poorly controlled joint. | Coordinate facing type and finish with gasket, bolting, assembly procedure, service, and piping-class approval. |
Continue the specification
Products, Grades, Applications, and Adjacent Standards
Product forms
Grade datasheets
Adjacent standards
Application briefs
Surface guidance
Buyer questions
Frequently Asked Questions
Does ASME B16.5 specify stainless flange material?
It provides material group and rating coordination for covered products, but the purchase order must separately name the material specification and exact grade, such as an applicable ASTM A182/A182M grade, together with project restrictions and certification.
Is ASME Class 150 a fixed pressure rating?
No. The applicable rating depends on the contract edition, material group, temperature, component type, governing code, and project conditions. The piping designer must select the class rather than converting the class label into one universal pressure value.
What must be stated for a weld-neck flange bore?
Give the mating pipe OD and wall or schedule, required bore, corrosion allowance where applicable, hub and weld-end detail, dimensional tolerance, and the piping-class or drawing reference.
Published by Tsingshan (Shandong) Iron & Steel Co., Ltd..Sources, update policy and technical limitations.
Quotation package
What to Include in the RFQ
- ASME B16.5 revision and project piping class
- NPS and pressure class
- Flange or flanged-fitting type
- Facing type, finish, and protection
- Bore, mating pipe OD/wall, hub, and weld end
- Material standard, grade, and heat treatment
- Tests, NDE, PMI, certificate, and traceability
- Quantity, marking, packing, gasket/bolting interface, and document index
Quote request
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