Preheat M270M Gr.345W — H16, Mid HI, ≤ 20 mm: 125°F

M270M Gr.345W / M270 Gr.50W

AASHTO M270M Gr.345W (M270 Gr.50W) is a weathering bridge steel with 345 MPa (50 ksi) yield that forms a protective oxide patina for unpainted bridge service. The copper-chromium-nickel alloying provides atmospheric corrosion resistance, eliminating lifetime repainting costs estimated at $15–25 per square foot per cycle. Weld filler must match the weathering composition (E8018-W2 or equivalent) for exposed joints. NFC preheat per Table 6.3 Group 1; FC per Tables 12.6/12.7 which carry higher preheat than the non-weathering grades.

Memahami Preheat FC untuk M270M Gr.345W / M270 Gr.50W

Weathering 345 MPa (50 ksi) bridge steel for unpainted service. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 125°F minimum preheat at ≤ 20 mm (3/4 in). Lower hydrogen levels (H4 < H8 < H16) allow lower preheat because less hydrogen enters the weld deposit. Similarly, higher heat input reduces preheat requirements because slower cooling rates give hydrogen more time to diffuse out.

Di Mana M270M Gr.345W / M270 Gr.50W Digunakan

Deployed in unpainted bridge plate girders across humid, coastal, and high-maintenance-cost environments. The weathering patina eliminates lifetime repainting cycles estimated at $15–25/sq ft per cycle. Weld filler must match the weathering composition (E8018-W2 or ER80S-G-W) for exposed joints to ensure the weld face develops the same protective oxide as the base metal. Conventional Gr.345W is being replaced by HPS345W in new designs due to superior weldability.

Kontrol Hidrogen H16 untuk M270M Gr.345W / M270 Gr.50W

Weathering Gr.345W (50W) at H16 is used for field splices when self-shielded FCAW is the only practical process due to wind exposure on elevated bridge erection. The significantly higher preheat at H16 — often 40–60°F above H4 — makes weather-window scheduling critical for winter field splice operations.

Mengapa Preheat Penting pada ≤ 20 mm (3/4 in)

Material up to 20 mm (3/4 in) covers most cross-frame angles, stiffener clips, lateral bracing members, and light bridge plate. At this thickness, hydrogen diffusion is efficient and preheat requirements are the lowest in Table 6.3 — 10°C (50°F) for both groups. In FC service, this thickness tier also carries the lowest preheat in Tables 12.4–12.7, starting at 40°C (100°F) for H4 consumables.

M270M Gr.345W / M270 Gr.50W pada ≤ 20 mm (3/4 in)

Gr.345W (50W) weathering steel at thin plate thickness appears in unpainted bridge bearing stiffeners and web attachment plates exposed to the atmosphere. Filler metal must match the weathering composition — E8018-W2 for SMAW or ER80S-G-W for GMAW. The patina development on thin plate is rapid (6–18 months) but requires proper drainage detailing to prevent pack rust between closely spaced plates.

Preheat Lebih Tinggi pada Penunjukan H16

Bahan habis pakai H16 mengizinkan hingga 16 mL hidrogen difusibel per 100g — tingkat tertinggi yang diizinkan untuk pengelasan FC jembatan. Pada ≤ 20 mm (3/4 in) dengan masukan panas 2.0–2.8 kJ/mm, preheat 125°F (50°C) mengkompensasi potensi hidrogen yang lebih tinggi.

Baja Jembatan Lain pada H16 2.0–2.8 kJ/mm · ≤ 20 mm (3/4 in)

M270M Gr.345W / M270 Gr.50W pada H16 2.0–2.8 kJ/mm

Coba Kombinasi Berbeda

Gunakan Kalkulator Preheat Jembatan D1.5 untuk mencari baja AASHTO M270, tingkat hidrogen, dan kombinasi masukan panas. Lihat juga Kalkulator Preheat D1.1 untuk baja struktural.

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