ASTM A320 B8M Class 2 insulated U-bolts are custom stainless steel pipe-support fasteners for projects that specify strain-hardened B8M bolting material together with a non-metallic barrier between the U-bolt assembly and the pipe. SINO-ALLOY can supply the bent U-bolt, matching nuts and washers, PTFE sleeve and backing pad, and a specified Xylan coating system as one drawing-controlled assembly. The non-grip version is used as a guide: it limits lateral movement while leaving designed clearance for axial thermal movement. Typical applications include offshore, marine, chemical-processing and low-temperature piping supports. Rod diameter, pipe clearance, leg length, thread length, coating grade and insulating components are customized after review of the pipe outside diameter, operating conditions and support drawing.
Product at a Glance
| Item | Available configuration | Selection note |
|---|---|---|
| Product type | Round-bend insulated U-bolt; grip or non-grip/guide arrangement | Function must be defined on the support drawing |
| U-bolt material | ASTM A320/A320M Grade B8M, Class 2 where specified | Material standard does not define the finished U-bolt geometry or assembly load |
| Nut option | ASTM A194/A194M Grade 8M where specified | Nut grade, class, dimensions and proof-load requirements must match the purchase specification |
| Isolation system | Machined or formed PTFE sleeve, backing pad and insulating washers; alternatives reviewed by application | Thickness and clearances affect finished inside width |
| Coating option | Specified Xylan fluoropolymer system on exposed metal and threaded components | Xylan grade, pretreatment, colour, film build and cure schedule require confirmation |
| Dimensional basis | Customer drawing or ASME B18.31.5 inch-series bent-bolt principles where applicable | Actual pipe OD—not NPS or DN alone—controls fit |
| Applications | Pipe guides, insulated hold-downs and corrosion-control support assemblies | Pipe reactions, vibration, temperature and support spacing require engineering review |
| Supply format | U-bolt with nuts, washers, sleeve and pad; inspection and packing to order | Components can also be supplied to an approved bill of materials |
Customization Note: The configurations and technical values above are for selection and quotation reference. Actual dimensions vary with the governing standard, actual pipe outside diameter, grip or non-grip design, sleeve and pad thickness, installation arrangement and project requirements. SINO-ALLOY can manufacture U-bolts to customer drawings, specifications, samples or confirmed installation conditions. Buyers may specify material grade and class, rod diameter, thread form, inside width, leg length, thread length, bend radius, Xylan grade, coating build, sleeve material and backing-pad details, subject to technical review.
What Does ASTM A320 B8M Class 2 Specify?
ASTM A320/A320M covers alloy-steel and stainless-steel bolting materials and bolting components for low-temperature service. Grade B8M is an austenitic stainless designation associated with molybdenum-bearing stainless steel; Class 2 identifies a strain-hardened condition. It is not simply another label for an ordinary commercial 316 stainless U-bolt.
The standard establishes material, heat-treatment or processing, mechanical-test and related requirements for the bolting material. It does not, by itself, define the inside width, leg length, thread length, bend radius, support clearance or allowable load of a pipe U-bolt. Those details must come from the approved drawing and the support design. Where inch-series bent-bolt geometry is relevant, ASME B18.31.5 provides general requirements and dimensional approaches for bent bolts, including U-bolts; custom configurations can still be identified by their specified dimensions, material and finish.
ASTM standards treat inch-pound and SI designations as separate systems. The purchase order should state whether ASTM A320 or A320M applies, and dimensions should not be assembled from rounded conversions. SINO-ALLOY keeps source inch dimensions at their specified precision and uses an exact factor of 25.4 only when a project requires a reference conversion to millimetres.
Why Combine B8M Class 2 with Insulation and Xylan Coating?
Each part of the assembly addresses a different selection problem. B8M Class 2 is a bolting-material requirement. The PTFE sleeve and pad create a non-metallic interface that can separate the pipe coating from the U-bolt and support steel. A correctly specified non-grip clearance allows the pipe to move axially through the guide. Xylan is a family of fluoropolymer coating systems used where controlled friction, corrosion resistance or thread performance is required.
These functions must not be collapsed into one blanket performance claim. A stainless substrate does not remove the need to assess galvanic couples. A sleeve does not automatically make an assembly a guide. A low-friction coating does not establish an allowable pipe movement or bolt torque. The complete arrangement must be checked against the pipe material, external coating, insulation, operating temperature, corrosion environment and calculated pipe reactions.
Xylan grade selection
PPG describes Xylan 1014 as a resin-bonded, high-temperature-resistant coating formulated to reduce friction and help prevent corrosion, with a less porous and harder surface than Xylan 1010. PPG describes Xylan 1070 as a dry film containing additional corrosion inhibitors and formulated for threaded components. These descriptions support selection, but they are not interchangeable project specifications. The coating grade shown by colour cannot be assumed, and the photographs on this page are not evidence of a particular dry-film thickness, cure cycle or corrosion-test result. The buyer should state the approved Xylan grade or performance specification; SINO-ALLOY will confirm the coating processor and inspection requirements before production.
How Does the Non-Grip U-Bolt Guide Work?
A non-grip U-bolt guide restrains the pipe laterally without tightening the curved bolt against the pipe as a rigid clamp. The inside width and installed height include intentional clearance after the sleeve is fitted. A backing pad separates the pipe from the support steel, while the U-bolt keeps the pipe within the permitted guide envelope.
The required clearance is a design input, not a generic catalogue allowance. It depends on pipe OD tolerance, external coating, insulation or sleeve build, expected movement, erection tolerance and the guide arrangement. Four-nut arrangements may be used where nuts above and below the support member set and lock the installed height, but the final detail must follow the project drawing. If the nuts are tightened until the sleeve grips the pipe, the assembly no longer performs as the intended low-friction guide.
Grip, Non-Grip and Half-Round Support Options
| Arrangement | Primary function | Key quotation inputs |
|---|---|---|
| Grip insulated U-bolt | Holds the pipe at the support with controlled contact through an isolating layer | Pipe OD, allowable contact pressure, sleeve material, tightening method and design reactions |
| Non-grip insulated U-bolt | Guides the pipe laterally while allowing specified axial movement | Cold and operating OD, required radial/vertical clearance, movement direction and nut arrangement |
| U-bolt with half-round support rod | Raises the pipe contact line and reduces the broad moisture-trapping contact area at the support | Rod profile and material, pipe coating, support steel width, loads and attachment details |
The non-grip insulated assembly described here is structurally different from SINO-ALLOY’s Xylan-coated U-bolt with a half-round support rod. Buyers comparing a plain metallic clamp can also review 316 stainless steel U-bolt clamps. Where the fluoropolymer covers the metal rather than acting as a removable sleeve and backing pad, see the separate PTFE-coated U-bolt configuration.
Dimensions and Drawing Control
Nominal pipe size is not a manufacturing diameter. The quotation should state the actual outside diameter of the bare pipe and identify every layer between the pipe and the metal U-bolt. For coated or insulated pipe, provide the finished outside diameter at the support location. The U-bolt inside width is then established from that diameter, the two sleeve wall thicknesses, the required guide clearance and the drawing tolerance.
Leg length must be checked against the pad, support-member thickness, washers, nut stack and required thread projection. Thread length must allow assembly without placing an incomplete thread or bend transition in a loaded nut position. Bend radius and straight-leg tangent points also matter because the material and class are not a substitute for manufacturable geometry. For Class 2 material, the production and verification route should be agreed before bending so that the ordered material condition and finished-part requirements remain technically coherent.
Materials, Components and Inspection
| Component | Reference option | Items to confirm |
|---|---|---|
| U-bolt body | ASTM A320/A320M B8M Class 2 where specified | Edition, diameter, dimensional system, material certification, bend and thread requirements |
| Nuts | ASTM A194/A194M Grade 8M where specified | Edition, size, dimensions, class/condition, proof-load and marking requirements |
| Washers | Stainless or insulating washers to drawing | Material, thickness, OD/ID and position in the nut stack |
| Sleeve and pad | PTFE or another approved non-metallic isolation system | Grade, thickness, temperature, chemical exposure, wear surface and attachment |
| Coating | Confirmed Xylan grade applied by a qualified coating processor | Pretreatment, colour, film build, cure, masking, inspection and repair criteria |
Customization Note: This component table is a quotation framework, not a universal bill of materials. Actual materials and technical values vary with the specified ASTM editions, pipe outside diameter, grip or non-grip function, insulation build, support arrangement and service environment. SINO-ALLOY can manufacture to an approved drawing, sample or project specification and can adapt rod diameter, inside width, leg length, thread length, thread form, coating and isolation components after technical review.
Inspection can include review of material certificates, dimensional inspection against the approved drawing, thread gauging, visual coating examination, dry-film-thickness checks where specified, and verification of the supplied component count. Any low-temperature impact testing, coating adhesion method, holiday test, salt-spray requirement or project inspection point must be stated in the inquiry; it is not implied by the product name or photograph.
Information Required for Quotation
- Pipe NPS or DN and exact pipe outside diameter, including coating or insulation at the support.
- Grip, non-grip/guide or hold-down function, plus required movement and installed clearance.
- ASTM A320/A320M edition, Grade B8M Class 2 requirement and applicable dimensional system.
- Rod diameter, inside width, leg length, bend radius, thread form, thread length and quantity.
- Nut and washer specifications, including ASTM A194/A194M Grade 8M where required.
- PTFE sleeve and pad grade, thickness, attachment and temperature/chemical conditions.
- Xylan grade, colour, coating build, pretreatment and inspection criteria.
- Support-member thickness, nut arrangement, pipe reactions, vibration, corrosion environment and operating temperature.
- Approved drawing, material-documentation requirements, inspection plan and export packing instructions.
Frequently Asked Questions
Is ASTM A320 B8M Class 2 the same as ordinary 316 stainless steel?
No. B8M is associated with molybdenum-bearing austenitic stainless steel, but ASTM A320 adds a defined bolting-material specification and Class 2 condition. The purchase order must state the required standard, grade, class and edition rather than relying only on “316 stainless steel.”
Does ASTM A320 define the U-bolt dimensions?
No. ASTM A320 governs bolting material requirements, not pipe-support geometry. U-bolt dimensions come from an approved drawing or an applicable bent-bolt dimensional standard such as ASME B18.31.5.
Can the Xylan coating grade be selected by colour?
No. Colour can be a visual identifier, but it does not prove the coating formulation. State the approved Xylan grade and the required pretreatment, film build, cure and inspection basis.
Can this assembly be used as a sliding guide?
Yes, when the support drawing provides the correct installed clearance and low-friction interfaces. The pipe movement, reactions, temperature, sleeve/pad properties and nut arrangement must be reviewed for the specific support.
Request a Drawing-Based Quotation
Send SINO-ALLOY the pipe outside diameter, support function, ASTM material requirements, U-bolt dimensions, PTFE sleeve and pad details, Xylan coating specification, operating conditions, quantity and drawing. We will review the complete assembly for manufacturability and prepare an RFQ response based on the confirmed standard, material condition, dimensions, coating process, inspection and packing requirements.
