U-Bolt Pipe Clamp A4-70 SS | DIN 3570 Marine | sinofastener
U-Bolt Pipe Clamp A4-70 Stainless Steel — DIN 3570 Marine
A4-70 stainless steel U-bolt pipe clamp manufactured per DIN 3570 for marine piping systems. Round bend U-bolt with two threaded legs and hex nuts, designed for clamping pipes, tubes, and cables to decks, bulkheads, and structural frames. Material conforms to ISO 3506-1 property class A4-70 (AISI 316/316L), providing pitting and crevice corrosion resistance in chloride-containing marine environments. Size range DN 20 through DN 500 (M6 to M36). Paired nuts per ISO 4032. SINOFASTENER supplies A4-70 U-bolts with full material traceability, mill test reports (EN 10204 3.1), and compliance documentation for shipyard project requirements.
What Is a U-Bolt Pipe Clamp?
A U-bolt pipe clamp is a round-bend, U-shaped fastener with two threaded legs extending from the bend. The bolt wraps around a pipe or cylindrical object and secures it to a flat surface, structural frame, or support bracket using two hex nuts on the threaded legs. Unlike conventional through-bolts that require holes in the clamped object, the U-bolt grips the outer surface directly, functioning as both clamp and anchor in a single component.
In marine piping systems, U-bolts serve as the primary pipe support and routing fastener throughout engine rooms, pump rooms, ballast systems, and deck piping networks. The A4-70 grade designation indicates austenitic stainless steel with molybdenum addition (AISI 316/316L family), providing superior resistance to chloride-induced pitting corrosion compared to A2-70 (304) grade fasteners.
Marine Applications
| Application | Vessel Area / System | Standard Reference |
|---|---|---|
| Seawater cooling pipe support | Engine room piping | DIN 3570; ASTM F593 Group 2 |
| Ballast water system pipe clamp | Double bottom / ballast tank piping | 46 CFR 56.60; DIN 3570 |
| Bilge and drain line routing | Lower deck piping | DIN 3570; ASTM F1155 |
| Deck drainage pipe clamp | Weather deck and superstructure | DIN 3570; ISO 14655 |
| Cable tray and conduit support | Electrical cable routing along bulkheads | DIN 3570 |
| Fire main line pipe clamp | Fire-fighting water main piping | SOLAS II-2; DIN 3570 |
| Handrail base and stanchion anchor | Deck handrail posts and stanchions | ISO 14143; DIN 3570 |
| Auxiliary machinery vibration support | Pump and compressor mounting | DIN 3570; ISO 8675 |
Application suitability determined by material properties per ISO 3506-1 and dimensional compliance per DIN 3570.
Specifications and Materials
| Parameter | Range / Value | Standard Reference |
|---|---|---|
| Product form | Round bend U-bolt with two threaded legs | DIN 3570 |
| Size range (thread diameter) | M6 through M36 | DIN 3570 Table 1 |
| DN range (pipe nominal size) | DN 20 through DN 500 | DIN 3570 Table 1 |
| Inside width (a) | 30 mm to 530 mm (per DN) | DIN 3570 Table 1 |
| Overall height (h) | 70 mm to 589 mm (per DN) | DIN 3570 Table 1 |
| Thread length (b) | 40 mm to 70 mm (per DN) | DIN 3570 Table 1 |
| Material property class | A4-70 (AISI 316/316L austenitic stainless) | ISO 3506-1 Table 3 |
| Tensile strength (Rm) | ≥700 MPa | ISO 3506-1 Table 3 |
| Yield strength (Rp0.2) | ≥450 MPa | ISO 3506-1 Table 3 |
| Carbon (C) | ≤0.08% | ISO 3506-1 Table 1 |
| Chromium (Cr) | 16.0 – 18.0% | ISO 3506-1 Table 1 |
| Nickel (Ni) | 10.0 – 14.0% | ISO 3506-1 Table 1 |
| Molybdenum (Mo) | 2.0 – 3.0% | ISO 3506-1 Table 1 |
| Manganese (Mn) | ≤2.0% | ISO 3506-1 Table 1 |
| Sulfur (S) | ≤0.030% | ISO 3506-1 Table 1 |
| Phosphorus (P) | ≤0.045% | ISO 3506-1 Table 1 |
| Silicon (Si) | ≤1.0% | ISO 3506-1 Table 1 |
| Hardness | ≤230 HV | ISO 3506-1 Table 3 |
| Included nuts | Two hex nuts per ISO 4032 | ISO 4032; ISO 898-2 |
| Thread tolerance | 6g | ISO 965-1 |
| Surface finish | Passivated (stainless steel) | ASTM A967 |
| Material traceability | EN 10204 3.1 mill test certificate | EN 10204 |
DIN 3570 Dimension Table (Selected Sizes)
| DN | Inside Width a (mm) | Thread d3 | Thread Length b (mm) | Height h (mm) | Pipe OD d1 (mm) | Inch Equiv. |
|---|---|---|---|---|---|---|
| DN 20 | 30 | M10 | 40 | 70 | 25 / 26.9 | 3/4" |
| DN 25 | 38 | M10 | 40 | 76 | 30 / 33.7 | 1" |
| DN 32 | 46 | M10 | 50 | 86 | 38 / 42.4 | 1 1/4" |
| DN 40 | 52 | M10 | 50 | 92 | 44.5 / 48.3 | 1 1/2" |
| DN 50 | 64 | M12 | 50 | 109 | 57 / 60.3 | 2" |
| DN 65 | 82 | M12 | 50 | 125 | 76.1 | 2 1/2" |
| DN 80 | 94 | M12 | 50 | 138 | 88.9 | 3" |
| DN 100 | 120 | M16 | 60 | 171 | 108 / 114.3 | 4" |
| DN 125 | 148 | M16 | 60 | 191 | 133 / 139.7 | 5" |
| DN 150 | 176 | M16 | 60 | 217 | 159 / 168.3 | 6" |
| DN 200 | 228 | M20 | 70 | 283 | 216 / 219.1 | 8" |
| DN 250 | 282 | M20 | 70 | 334 | 267 / 273 | 10" |
| DN 300 | 332 | M20 | 70 | 385 | 318 / 323.9 | 12" |
| DN 350 | 378 | M24 | 70 | 435 | 355.6 / 368 | 14" |
| DN 400 | 428 | M24 | 70 | 487 | 406.4 / 419 | 16" |
| DN 500 | 530 | M24 | 70 | 589 | 508 / 521 | 20" |
All dimensions per DIN 3570 Table 1. Custom inside width, height, and leg length available per shipyard spool drawing.
Why Choose SINOFASTENER for Marine U-Bolts?
Precision bend control: Round bend radius maintained per DIN 3570 tolerance, ensuring parallel leg alignment and consistent nut engagement without cross-threading.
Grade A4-70 verified: Every batch tested against ISO 3506-1 mechanical and chemical requirements. Mill test certificates (EN 10204 3.1) provided with shipment.
Chloride corrosion resistance: Molybdenum content (2.0–3.0%) per ISO 3506-1 Table 1 provides pitting resistance equivalent (PREN) suitable for seawater and ballast water environments.
Full size range: Stocked and custom-made sizes from DN 20 (M6) to DN 500 (M24), covering all standard marine pipe diameters per DIN 3570 Table 1.
Annual capacity: 50,000 tons of marine fasteners, supporting high-volume shipyard project orders with consistent lead times.
Standards Reference
| Standard | Scope |
|---|---|
| DIN 3570 | U-bolt form, dimensions, and tolerances (round bend pipe clamp bolts) |
| ISO 3506-1 | Mechanical properties of stainless steel fasteners — Bolts, screws, and studs (property class A4-70) |
| ASTM F593 | Stainless steel bolts, hex cap screws, and studs (Group 2, Type 316/316L) |
| ASTM A967 | Chemical passivation treatment for stainless steel parts |
| ISO 4032 | Hexagon regular nuts (style 1) — for included nuts |
| ISO 898-2 | Mechanical properties of fasteners — Nuts with coarse thread |
| ISO 965-1 | General purpose metric screw threads — Tolerances |
| EN 10204 | Types of inspection documents (mill test certificates) |
| ASTM F1155 | Standard practice for selection and application of piping materials for shipboard systems |
FAQ
Q1: What does A4-70 mean for U-bolts?
A4-70 is a property class designation per ISO 3506-1."A4"indicates austenitic stainless steel of the AISI 316/316L family with molybdenum (Cr 16–18%, Ni 10–14%, Mo 2–3%)."70"indicates minimum tensile strength of 700 MPa. This grade provides superior chloride corrosion resistance compared to A2-70 (304 family), making it the preferred material for marine and offshore environments.
Q2: Can A4-70 U-bolts be used on copper-nickel piping?
Yes. A4-70 stainless steel U-bolts are suitable for clamping copper-nickel (CuNi 90/10, CuNi 70/30) piping commonly used in seawater cooling systems. The material combination avoids galvanic corrosion when properly specified per the shipyard piping material selection guide (ASTM F1155).
Q3: What is the difference between round bend and square bend U-bolts?
DIN 3570 defines the standard U-bolt form with a round bend radius. Round bend U-bolts provide uniform contact pressure distribution around the pipe circumference, reducing point loading. Square bend U-bolts are available as an optional form for specific structural mounting requirements but are not covered by the standard DIN 3570 dimension table.
Q4: Do you supply matching nuts with the U-bolts?
Yes. Each U-bolt is supplied with two hex nuts per ISO 4032, in matching A4-70 stainless steel. Lock nuts (ISO 7040 nylon insert or ISO 7042 all-metal) are available on request for vibration-prone engine room applications. Custom nut configurations per shipyard specification are also accepted.
Contact SINOFASTENER
Ningbo Zhonglian Fastener Manufacture Co., Ltd.
Email: sales@sinofastener.com | bobo@sinofastener.com
Tel: 0574-86592068
Website: www.zlfastener.com | www.sinofastener.com
