GRADE GUIDE · SA387 GR11
SA387 Grade 11 is 1.25Cr-0.5Mo pressure-vessel plate — the ASME chrome-moly grade for refinery exchangers, boilers and reactors running hot, roughly up to 560 °C. The chromium resists oxidation and hydrogen attack; the molybdenum holds strength at temperature where carbon steel fades.
Also listed as: ASME SA387-11 · A387 Gr.11 · 13CrMo4-5 (near) · 1.7335 (near)
Stock turns over piece by piece — what's listed is what exists. Post the spec you need and we match it against incoming material; you're alerted the moment something lands.
Above about 400 °C, plain carbon plate like A516 starts losing the plot — creep, oxidation, and in hydrogen service, internal attack on the steel itself. Grade 11's alloying was designed for exactly that regime, which is why refinery pressure vessels, heat-exchanger shells, and power-plant components across the Gulf's energy sector are rolled from it. It comes in Class 1 and the stronger Class 2 (≈ 310 MPa yield); the certificate states which.
Fabrication is a discipline of its own: preheat before welding, matching chrome-moly consumables, and post-weld heat treatment on code work are the norm, not the exception. Off-cut drops from vessel and exchanger fabricators are the natural supply — certified plate in odd sizes that code shops can nest smaller parts from, at a fraction of a fresh mill plate.
Heat-treatment condition and strength: Class 2 is normalised and tempered to higher yield and tensile minimums. Code calculations name the class, so match the certificate to the design, not just the grade number.
Higher temperatures and harsher hydrogen partial pressures: Gr22's 2.25Cr-1Mo chemistry extends both limits. The Nelson curves used in refinery design draw the exact boundary for hydrogen service.
No — chrome-moly plate expects preheat, low-hydrogen matching consumables and, on code vessels, mandatory post-weld heat treatment. Budget the procedure before buying the plate.