ASTM A515 Grade 70

Overview

Designation system

ASTM grade designation; Grade 70 is the inch-pound designation and Grade 485 is the corresponding SI designation

Product forms

Rolled steel plate for welded boilers and other pressure vessels, Finished plate processed from coil, subject to additional ASTM A20/A20M controls

Condition

As-rolled, normally for thickness 50 mm [2 in.] and under, Normalized, optional at 50 mm [2 in.] and under and mandatory over that thickness, Stress relieved, when ordered, Normalized and stress relieved, when ordered

Density

7.85 g/cm³ (Representative value for carbon steel; not a requirement of ASTM A515/A515M.)

What the designation controls

ASTM A515/A515M covers carbon-silicon steel plate primarily for intermediate- and higher-temperature service in welded boilers and other pressure vessels. Grade 70 [Grade 485] identifies the highest of its three strength levels; the number denotes the lower bound of the specified tensile-strength range in ksi or MPa, not yield strength, design allowable stress or service temperature.

The product specification must be used together with ASTM A20/A20M. A20/A20M supplies the common pressure-vessel plate rules for ordering, manufacture, test sampling, retests, dimensional tolerances, surface quality, repair, marking and certification. Where the two specifications conflict, A515/A515M governs. The inch-pound and SI systems are independently standard; an order should identify either A515 or A515M and should not mix converted requirements from both systems.

For ASME Boiler and Pressure Vessel Code construction, the adopted material specification is SA-515/SA-515M in Section II, Part A. Code acceptability, allowable stress, temperature limits, impact-test exemptions and fabrication rules must be taken from the applicable ASME Code edition—not inferred from the ASTM material specification.

Manufacture and delivery condition

The required coarse austenitic grain-size practice is intentional and materially significant. It differentiates A515 from fine-grain pressure-vessel steels designed around improved notch toughness. Normalization can refine the final ferrite-pearlite structure and reduce rolling-related variability, but it does not transform A515 into A516 or create an unstated impact-toughness guarantee.

Chemical composition requirements

These are specification limits rather than a typical mill aim. Carbon can be appreciably higher than in many modern fine-grain pressure-vessel plates, especially at greater thickness. Weldability assessment should therefore use the actual certified heat analysis, not a nominal grade-based carbon-equivalent value. The A515 chemistry table also does not by itself define every residual element needed for a complete weldability or service-environment assessment.

Room-temperature tensile requirements

The specified tensile properties are material-acceptance requirements, not pressure-design allowable stresses. Elevated-temperature allowable stresses and time-dependent design limits are code- and edition-specific.

Toughness and service-temperature implications

The base A515/A515M specification requires tension testing but does not establish a minimum Charpy V-notch energy, a test temperature, a nil-ductility transition temperature or a fracture-toughness value. Consequently, compliance with Grade 70 alone does not demonstrate suitability for startup, shutdown, hydrotest, upset or ambient conditions where the metal may be cold and highly stressed. The governing construction code must be checked for impact-testing rules and exemptions, and project-specific impact requirements should be stated in the purchase order where needed.

The phrase “intermediate- and higher-temperature service” describes the intended application of the plate specification; it is not a standalone service-temperature rating. Maximum design temperature may be controlled by the construction code, allowable-stress tables, oxidation, graphitization risk, creep or stress-rupture behavior, process environment, weld metal and heat-affected zones. Those limits cannot be derived from the room-temperature Grade 70 tensile table.

Where low-temperature toughness is important, ASTM A516 Grade 70 is frequently considered because it is a fine-grain pressure-vessel plate specification intended for improved notch toughness. It is not an automatic substitute: chemistry, heat treatment, code listing, certification, impact requirements and the approved design basis must all be reviewed.

Welding, forming and thermal processing

A515 plate is intended to be fusion welded, but the material specification does not supply a welding procedure. The WPS and PQR must be qualified to the applicable construction code and should account for actual heat chemistry, plate thickness, joint restraint, welding process, consumable hydrogen level, heat input, preheat and interpass control. The grade's relatively high permitted carbon content makes assumptions based only on its 260 MPa yield strength unsafe; actual mill-test chemistry should be used for carbon-equivalent or other weldability assessments.

Postweld heat treatment is governed by the construction code, component thickness, service and qualified welding procedure. If plates or test coupons are to receive simulated fabrication heat treatments, the required thermal cycle and testing condition should be specified at purchase. Repeated or prolonged thermal cycles can alter strength and toughness, so properties certified only in the original delivery condition may not represent the completed vessel.

Cold and hot forming procedures must preserve the required final material condition. Heavy cold deformation may require heat treatment under the governing construction code. Hot forming of plate supplied or required as normalized needs a controlled finishing or subsequent normalizing cycle capable of restoring the specified condition. Forming limits and minimum bend radii are not defined by A515 Grade 70 alone; ASTM A20/A20M guidance, mill recommendations and the fabrication code should be considered.

Inspection, testing and purchasing controls

On receipt, confirm that the certificate and plate marking agree on specification, grade, heat number, dimensions and heat-treatment condition. Particular attention should be given to plates over 50 mm [2 in.], which must be normalized, and to coil-derived plates, for which the finished-plate processor assumes specific qualification and certification responsibilities.

Substitution and specification pitfalls

A515 Grade 70 and A516 Grade 70 share the same nominal tensile range and minimum yield strength, but they are not the same grade. A515 requires coarse austenitic grain-size practice and targets intermediate- and higher-temperature service; A516 requires fine-grain practice and is intended where improved notch toughness is important. Their chemistry limits, heat-treatment framework, UNS numbers and code treatment also differ. A strength-only comparison is therefore insufficient for substitution.

Likewise, ASTM A515 Grade 70 and ASME SA-515 Grade 70 should not be treated as interchangeable labels without checking editions. SA-515 is the ASME-adopted material specification used within the BPVC framework; procurement and design documents should use the designation required by the construction code and verify that the material certification cites an accepted specification edition.

Historical certificates may reflect older editions with different phosphorus, sulfur, manganese, silicon or scope provisions. Acceptance of legacy material requires comparison against the edition permitted by the governing construction code or project specification, not merely recognition of the grade name.

Related designations

A related designation or cross-standard counterpart is not a declaration of equivalence; confirm the standard, product form and condition before substituting.