AASHTO/AWS D1.5:2025 · Table 12.8 · Fracture-Critical

M270M HPS690W Preheat — 2.0–2.8 kJ/mm, 25–50 mm: 250–400°F

Fracture-critical preheat requirement for M270M HPS690W / M270 HPS100W at 25–50 mm (1–2 in) thickness, per AASHTO/AWS D1.5:2025, the Bridge Welding Code.

Built on AWS D1.5:2025 — every value traced to the clause.

Fracture-Critical Preheat Range

250–400°F / 120–200°C

Table 12.8 — 2.0–2.8 kJ/mm heat input at 25–50 mm (1–2 in) thickness

AASHTO/AWS D1.5M/D1.5:2025 Table 12.8

Both minimum AND maximum preheat/interpass must be maintained. Exceeding 400°F risks degrading the Q&T microstructure.

Reference tool. Verify against project-applicable edition and Engineer-approved WPS.

AASHTO M270 High-Performance Grades

M270M HPS690W / M270 HPS100W

AASHTO M270M HPS690W (M270 HPS100W) is the highest-strength bridge steel at 690 MPa (100 ksi) yield, reserved for the most demanding long-span and cable-stayed bridge applications. It follows a completely different FC preheat table (Table 12.8) with min-max ranges and many prohibited thickness-heat input combinations marked with “—”. Table 12.8 requires H4 or H8 designated consumables; H16 is not permitted. NFC preheat per Table 6.3 Group 2; maximum interpass per Table 6.4 is 205°C (400°F) for material up to 40 mm, 230°C (450°F) above.

Bridge Applications

Where M270M HPS690W / M270 HPS100W Is Used

Reserved for the most demanding long-span and cable-stayed bridge applications where maximum weight reduction justifies the material cost premium and fabrication complexity. Table 12.8 imposes both minimum AND maximum preheat limits, and many thickness-heat input combinations are outright prohibited. Fabricators must plan weld procedures around the permitted combinations before cutting plate. Filler metals must carry the H4 or H8 supplemental designator — H16 is not permitted for HPS690W FC applications.

Fabrication Detail

M270M HPS690W / M270 HPS100W at 25–50 mm (1–2 in)

HPS690W (HPS100W) at 40–65 mm is the thickest plate commonly used with this grade. Many thickness-heat input combinations at this tier are prohibited in Table 12.8 — the fabricator must verify that the planned welding procedure matches a permitted cell before beginning production. The permitted preheat ranges narrow further, often spanning only 50°F between minimum and maximum, making continuous temperature monitoring essential.

Preheat Range Required

Min–Max Preheat Control for M270M HPS690W / M270 HPS100W

Highest-strength 690 MPa (100 ksi) bridge steel with restricted FC combinations. Table 12.8 specifies a preheat RANGE of 250–400°F for this thickness and heat input combination. Unlike other FC grades, HPS690W requires both minimum AND maximum preheat control because the Q&T microstructure is sensitive to both excessive and insufficient heat. Many thickness-heat input combinations are prohibited ("—" in the table) because no safe preheat window exists — the steel cannot be reliably welded under those conditions.

Other Thicknesses

M270M HPS690W / M270 HPS100W at 2.0–2.8 kJ/mm

Interactive Calculator

Try Different Combinations

Use the D1.5 Bridge Preheat Calculator to look up any AASHTO M270 steel, hydrogen level, and heat input combination. Also see the D1.1 Preheat Calculator for structural steel.

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Related Guides

FAQ

What is the preheat range for HPS690W at 25–50 mm (1–2 in) with 2.0–2.8 kJ/mm?

D1.5 Table 12.8 requires a preheat range of 250–400°F (120–200°C) for HPS690W at 25–50 mm (1–2 in) with 2.0–2.8 kJ/mm heat input. Both minimum AND maximum must be controlled.

Why does HPS690W have a maximum preheat limit?

HPS690W achieves its 690 MPa (100 ksi) strength through quenching and tempering. Excessive preheat can soften the tempered microstructure in the heat-affected zone, reducing the steel's strength below the design minimum. The maximum limit of 400°F (200°C) protects this Q&T condition.

D1.5:2025 reference data. Not affiliated with AWS or AASHTO.