التسخين المسبق M270M Gr.345 — H16، Low HI، > 60 mm: 350°F

M270M Gr.345 / M270 Gr.50

AASHTO M270M Gr.345 (M270 Gr.50) is the standard bridge plate and shape grade with 345 MPa (50 ksi) minimum yield, corresponding to ASTM A709 Gr.50. It is the baseline strength for modern highway bridge design per AASHTO LRFD. Used for plate girder flanges, webs, floor beams, cross-frames, and splice plates. Flanges on large plate girders routinely reach 50–75 mm (2–3 in) thick, making preheat compliance at upper thickness tiers a significant production consideration. NFC preheat per Table 6.3 Group 1; FC per Tables 12.4/12.5.

فهم التسخين المسبق FC لـ M270M Gr.345 / M270 Gr.50

Standard 345 MPa (50 ksi) bridge plate for girders and floor beams. Under D1.5 fracture-critical requirements (Clause 12), the combination of H16 hydrogen designation and this heat input band requires 350°F minimum preheat at > 60 mm (> 2½ 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.

أين يُستخدم M270M Gr.345 / M270 Gr.50

Standard for highway bridge plate girder flanges, box girder webs, cross-frame angles, bearing sole plates, and splice plates in bolted-welded connections. Gr.345 (50) is the baseline strength for modern AASHTO LRFD bridge design. Flange butt splices, web-to-flange continuous fillet welds, and bearing stiffener clips are the dominant weld types in girder fabrication. Girder flanges typically range from 20 to 75 mm (3/4 to 3 in) thick with widths from 300 to 750 mm (12 to 30 in), requiring extended preheat soak times on thicker flange splices.

التحكم في الهيدروجين H16 لـ M270M Gr.345 / M270 Gr.50

Gr.345 (50) at H16 requires the highest FC preheat in the standard grade range. The elevated preheat compensates for the substantial hydrogen potential but adds significant production cost on thick girder flanges. Most fabricators avoid H16 for shop work, reserving it only for field processes where lower-hydrogen alternatives are not feasible.

لماذا يهم التسخين المسبق عند > 60 mm (> 2½ in)

Material over 65 mm (2-1/2 in) includes the heaviest bridge girder flanges and box-section walls. Table 6.3 requires 110°C (225°F) for both groups at this thickness. Extended preheat soak time is necessary to achieve uniform through-thickness temperature. FC preheat for the heaviest sections reaches 180–200°C (350–400°F) at the H16 hydrogen level.

M270M Gr.345 / M270 Gr.50 عند > 60 mm (> 2½ in)

Gr.345 (50) above 65 mm represents the heaviest plate girder flanges on long-span bridges. At 75–100 mm flange thickness, each CJP splice requires 80+ weld passes with continuous interpass monitoring. Preheat soak-through needs heating mats or induction coils because torch heating alone cannot maintain uniform temperature through 3+ inches of plate. Production rates drop to 1–2 splices per shift at this thickness, making preheat efficiency a major scheduling factor.

تسخين مسبق أعلى بتصنيف H16

المواد المستهلكة H16 تسمح بحد أقصى 16 مل من الهيدروجين القابل للانتشار لكل 100 غ — أعلى مستوى مسموح به للحام FC للجسور. عند > 60 mm (> 2½ in) بمدخل حراري 1.2–2.0 kJ/mm، التسخين المسبق 350°F (180°C) يعوض عن إمكانية الهيدروجين الأعلى.

فولاذ جسور أخرى عند H16 1.2–2.0 kJ/mm · > 60 mm (> 2½ in)

M270M Gr.345 / M270 Gr.50 عند H16 1.2–2.0 kJ/mm

جرّب تركيبات مختلفة

استخدم حاسبة التسخين المسبق D1.5 للجسور للبحث عن أي فولاذ AASHTO M270 ومستوى هيدروجين وتركيبة مدخل حراري. انظر أيضاً حاسبة التسخين المسبق D1.1 للفولاذ الإنشائي.

أدلة ذات صلة