ASTM A387 Grade 11 Class 1 Steel Plate — Specification, Heat Treatment and

ASTM A387 Grade 11 Class 1: keep the alloy and strength class
together

SHH STEEL's Grade 11 Class 1 product page concerns chromium-
molybdenum pressure-vessel plate, not structural carbon plate and not
stainless steel. The nominal alloy description is 1.25Cr-0.5Mo.
ASTM's published A387/A387M scope identifies this family as plate
intended primarily for welded boilers and pressure vessels designed
for elevated-temperature service. A purchase inquiry should identify
the complete designation, including Class 1, rather than stopping at
“A387 Grade 11.”

What distinguishes this plate

Grade and class answer different questions. Grade 11 identifies the
alloy family; Class 1 identifies the lower tensile-strength class
within that grade. Class 2 is not an automatic upgrade, and Class 1
is not acceptable simply because its chemistry resembles the
requested Class 2 material. The actual drawing, design calculation
and purchasing specification determine which class is appropriate.
For ASME equipment, state the required SA-387 designation and
governing edition explicitly, and require the offered certification
to match.

The SHH STEEL page lists Grade 11 heat-analysis limits of chromium
1.00–1.50%, molybdenum 0.45–0.65%, carbon 0.05–0.17% and silicon
0.50–0.80%, by mass. These are heat-analysis limits, not the measured
composition of a particular shipment. Product-analysis allowances are
different and should be evaluated using the applicable standard
rather than compared indiscriminately with the heat-analysis column.
Grade 12 has a different chromium and silicon window; a general “Cr-
Mo” description cannot establish equivalence.

Strength values need the right context

For Class 1, the company technical page lists tensile strength of
415–585 MPa and minimum yield strength of 240 MPa. Treat these as
published material requirements to reconcile with the contractual
edition, ordered thickness, test condition and certification. They
are not allowable stresses for a pressure-vessel calculation or
evidence of creep life. ASTM's scope states that maximum thickness is
limited by the composition's ability to meet the specified mechanical
properties; a single grade name therefore does not prove unrestricted
thickness capability.

Delivery condition is part of the purchase

The product page describes thermally treated delivery, including
annealed or normalized-and-tempered routes, with other permitted
routes subject to the governing specification. Ask which route is
proposed and require it to be recorded in the documentation. Where
tempering applies, the page identifies 620°C as the minimum tempering
temperature for Grade 11. This is not a universal fabrication PWHT
instruction, and it should not be used to set a welding procedure
without engineering review.

Vessel fabrication can expose the plate to additional thermal cycles.
If the design requires simulated post-weld heat treatment of test
coupons, specify the cycle, number of cycles and acceptance basis
before quotation. Otherwise, a satisfactory tensile result in the
original delivered condition may not answer the buyer's actual
question about performance after fabrication heat treatment.

Applications and fabrication planning

Possible uses include boiler shells and elevated-temperature
pressure-vessel courses where the approved material specification
calls for this exact grade and class. Service suitability also
depends on pressure, temperature, corrosion allowance and the process
environment. The alloy designation alone establishes neither sour-
service qualification nor suitability for every hydrogen-containing
process. Those requirements need a specific materials review.

Welding should be covered by the fabricator's qualified procedure.
The responsible engineer must establish preheat, interpass control,
consumables and any PWHT against the construction code and component
details. A procedure for ordinary carbon steel should not be assumed
suitable merely because both products are plates.

Inspection and inquiry checklist

Request the required inspection document, such as EN 10204 3.1 where
specified, heat-number traceability, heat analysis, mechanical
results and delivered heat-treatment condition. If impact testing is
required, define temperature, energy, orientation and specimen
location. Specify ultrasonic testing with its method and acceptance
level, and identify any third-party witness points. None of these
additional services is implied as an automatic inclusion.

Send nominal thickness, width, length, quantity, edge condition,
tolerance basis and minimum-thickness constraints with the inquiry.
Include the standard edition, Class 1 designation, intended service
and fabrication heat-treatment requirements. Ask for confirmation of
actual offered material, dimensions and schedule; no inventory,
price, mill approval or blanket certification commitment is
represented here.

Product information: https://www.steelspecs.com/products/astm-a387-
, grade-11-class-1-steel-plate/
Company website: https://www.steelspecs.com/

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