ASTM A516 Grade 55

Killed, fine-grain carbon steel plate for welded pressure vessels · ASTM A516/A516M-25 — product specification · ASTM A20/A20M — general requirements for pressure-vessel plate · ASME SA-516/SA-516M — ASME Code counterpart, subject to the edition adopted by the construction code

ASTM A516 Grade 55 is the lowest-strength grade in the A516 family of weldable carbon-steel pressure-vessel plate. It combines a minimum tensile strength of 55 ksi [380 MPa] with relatively low thickness-dependent carbon limits and fine-grain, killed-steel practice. Its specification must be read together with ASTM A20/A20M: heat-treatment condition, plate thickness, unit system, impact testing, ultrasonic examination and any simulated fabrication heat treatment must be defined when ordering. Despite the specification’s emphasis on improved notch toughness, Charpy acceptance values are not part of the basic Grade 55 requirements unless invoked by the purchase order or governing construction code.

55–75 ksi [380–515 MPa]Specified tensile strength · The grade number denotes the lower tensile-strength limit, not yield strength.
30 ksi [205 MPa]Minimum yield strength · Determined by the specified offset or extension-under-load method.
Normalize above 1.50 in. [40 mm]Heat-treatment threshold · Thinner plate is normally as-rolled unless another condition or notch-toughness testing requires normalization.
Not automatic under the base specificationImpact testing · Charpy testing is a supplementary or code-driven requirement; temperature, orientation and acceptance criteria must be stated.
No fixed numerical maximum in ASTM A516/A516M-25Maximum thickness · Thickness is limited by the ability of the composition and processing route to satisfy the required properties.
ASTM A516/A516M-25Standard edition · Approved March 1, 2025; ASME construction must use the SA-516 edition adopted by the applicable Code edition.

Overview

Designation system: ASTM product specification; Grade 55 is the inch-pound designation and Grade 380 is the corresponding SI designation
Product forms: Hot-rolled plate, Cut-to-length plate processed from coil
Condition: As-rolled, normally permitted through 1.50 in. [40 mm], Normalized, optional through 1.50 in. [40 mm] and mandatory above that thickness, Stress relieved, when ordered, Normalized and subsequently tempered after purchaser-approved accelerated cooling
Density: 7.85 g/cm³ (Representative engineering value for carbon steel; density is not a specified A516 Grade 55 acceptance requirement.)

What the designation defines

A516/A516M is a plate product specification, not a general-purpose structural-steel designation. It covers carbon-steel plate intended primarily for welded pressure vessels in moderate- and lower-temperature service where notch toughness is important. Grade 55 identifies the lowest of the four A516 strength levels. The designation applies to finished plate; coil itself is not qualified until a processor has converted it into individual plates and completed the applicable testing, inspection, heat treatment, marking and certification.

How the governing documents divide responsibility

Document	Function	Practical consequence
ASTM A516/A516M	Defines grade-specific scope, heat treatment, chemistry, tensile properties and available supplementary requirements.	The purchase order should identify Grade 55 or Grade 380, the edition and one unit system.
ASTM A20/A20M	Provides common pressure-vessel plate rules for ordering, testing, retesting, dimensional tolerances, workmanship, repair, marking and certification.	Compliance with A516 alone cannot be assessed without the applicable A20/A20M requirements.
ASME SA-516/SA-516M	ASME Section II material specification used for construction to an ASME Boiler and Pressure Vessel Code section.	ASTM and ASME markings should not be treated as interchangeable without checking the construction-code edition and material certification.
Applicable construction code	Controls design allowable stresses, minimum design metal temperature rules, impact-test exemptions, welding qualification and fabrication heat treatment.	A516 certification by itself does not establish suitability for a particular vessel design or service temperature.

Where A516 conflicts with A20/A20M, the A516 product-specific requirement governs.

Mandatory composition requirements

Grade 55 carbon and manganese limits by ordered thickness

Ordered thickness	Carbon, maximum — heat and product analysis	Manganese — heat analysis	Manganese — product analysis
1/2 in. [12.5 mm] and under	0.18%	0.60–0.90%	0.55–0.98%
Over 1/2 to 2 in. [12.5 to 50 mm], inclusive	0.20%	0.60–1.20%	0.55–1.30%
Over 2 to 4 in. [50 to 100 mm], inclusive	0.22%	0.60–1.20%	0.55–1.30%
Over 4 to 8 in. [100 to 200 mm], inclusive	0.24%	0.60–1.20%	0.55–1.30%
Over 8 in. [200 mm]	0.26%	0.60–1.20%	0.55–1.30%

Carbon limits apply to both heat and product analyses. The permitted carbon level increases with thickness to support through-thickness strength and hardenability.

Other specified elements

Element	Heat analysis	Product analysis	Applicability
Phosphorus	0.025% maximum	0.025% maximum	All Grade 55 thicknesses
Sulfur	0.025% maximum	0.025% maximum	All Grade 55 thicknesses
Silicon	0.15–0.40%	0.13–0.45%	All Grade 55 thicknesses

These are specification limits, not typical mill targets.

For each 0.01 percentage-point reduction below the applicable maximum carbon content, manganese may exceed its stated maximum by 0.06 percentage point, up to 1.50% by heat analysis and 1.60% by product analysis. This allowance means that weldability assessments should use the actual certified chemistry rather than only the basic table limits.

A516 Grade 55 is produced as killed steel and must satisfy the fine-austenitic-grain-size requirements of A20/A20M. The specification does not impose a general carbon-equivalent maximum for ordinary Grade 55 plate. Carbon equivalent, residual-element restrictions or tighter chemistry limits therefore have to be invoked separately when required by welding practice, sour or hydrogen service, project specifications or the governing code.

Strength, ductility and test interpretation

Room-temperature tensile requirements

Property	Inch-pound requirement	SI requirement	Qualification
Tensile strength	55–75 ksi	380–515 MPa	Specified range
Yield strength, minimum	30 ksi	205 MPa	0.2% offset or 0.5% extension-under-load method
Elongation in 8 in. [200 mm], minimum	23%	23%	Subject to the elongation adjustments in A20/A20M
Elongation in 2 in. [50 mm], minimum	27%	27%	Subject to the elongation adjustments in A20/A20M

ASTM treats inch-pound and SI systems separately. Values from the two systems must not be mixed when determining conformity.

The tensile requirements apply to the plate as represented by specification test specimens; they are not minimum properties guaranteed at every location, orientation or through the full plate thickness. Test frequency, specimen location, orientation, retesting and special provisions for plate produced from coil are governed by A20/A20M. The relatively low Grade 55 strength can support ductility and forming objectives, but it usually produces a greater required design thickness than a higher-strength A516 grade when allowable stress controls.

The 55 in “Grade 55” is the minimum tensile strength in ksi. It must not be interpreted as a 55 ksi minimum yield strength.

Heat treatment and its effect on specification

Permitted or required delivery condition

Plate thickness or circumstance	A516 requirement	Ordering implication
1.50 in. [40 mm] and under	Normally supplied as-rolled; may be ordered normalized, stress relieved, or both.	State the required condition rather than relying on a supplier’s normal practice.
Over 1.50 in. [40 mm]	Normalization is mandatory.	Confirm the normalized condition and associated test results on the material certificate.
1.50 in. [40 mm] and under when notch-toughness tests are required	Normalization is required unless the purchaser specifies otherwise.	Any departure should be deliberate and compatible with the governing construction code.
Accelerated cooling used to improve toughness	Permitted only with purchaser approval and followed by tempering at 1100–1300 °F [595–705 °C].	The route and final condition should be clearly reported and accepted before supply.

Condition is a material part of the order. As-rolled and normalized Grade 55 plate may meet the same basic tensile table, but they should not be assumed to have identical grain structure, toughness distribution, forming response or behavior after fabrication heat cycles. If the completed vessel will receive post-weld heat treatment, Supplementary Requirement S3 can be used to require mechanical-test coupons to undergo a simulated thermal treatment representative of fabrication.

Notch toughness and examination options

The reference to improved notch toughness in the scope describes the intended material family; it is not a universal certified Charpy energy at a stated temperature. The base A516 Grade 55 requirements contain no mandatory Charpy test temperature or absorbed-energy value. When toughness matters, the purchaser or construction code must define the testing requirement, including temperature, specimen orientation, specimen size where thickness is limiting, acceptance criteria, test frequency and any required thermal simulation.

Frequently relevant supplementary requirements

Requirement	Purpose	Important limitation
S2 — Product analysis	Confirms chemistry on the finished product in addition to heat analysis.	Must be specified in the order.
S3 — Simulated post-weld heat treatment	Tests material after a specified simulated fabrication heat cycle.	The purchaser must define the intended thermal treatment adequately.
S4.1 — Additional tension test	Provides additional mechanical-property sampling.	Does not replace a project-specific sampling plan where one is needed.
S5 — Charpy V-notch impact test	Adds notch-toughness verification.	Test temperature and acceptance requirements must come from the order or governing code.
S6 — Drop-weight test	Assesses nil-ductility transition behavior for plate 0.625 in. [16 mm] and thicker.	Applicable only when expressly invoked.
S7 — High-temperature tension test	Provides tensile data at an ordered elevated temperature.	It does not by itself establish code allowable stress.
S8 — ASTM A435/A435M straight-beam UT	Provides ultrasonic examination to the referenced plate standard.	The required examination and acceptance level must be clearly ordered.
S11 — ASTM A577/A577M angle-beam UT	Examines plate using the referenced angle-beam procedure.	Useful for specific discontinuity orientations; not a generic substitute for straight-beam UT.
S12 — ASTM A578/A578M straight-beam UT	Provides straight-beam examination with selectable acceptance levels for special applications.	Specify the required acceptance level and any supplementary scanning requirements.

Supplementary requirements do not apply unless invoked by the purchase order.

Fabrication and welding considerations

A516 Grade 55 is intended for fusion-welded pressure equipment and its comparatively low carbon limits are favorable to weldability. Nevertheless, A516 does not prescribe a universal welding consumable, preheat temperature, heat input, interpass temperature or post-weld heat-treatment cycle. Those controls depend on actual chemistry, thickness, joint restraint, hydrogen level, welding process, required toughness, service environment and the governing construction code. Welding must therefore be performed under a qualified procedure rather than from the grade designation alone.

For forming, the relevant material certificate should be reviewed for delivery condition, actual strength and chemistry before establishing bend or head-forming procedures. Heavy cold forming can reduce toughness and introduce residual stress; hot forming or subsequent heat treatment can alter the certified condition. Where forming or post-weld heat treatment is severe, qualification using representative thermal cycles and sufficient mechanical testing is more reliable than assuming that the original plate certificate remains fully representative.

IIW carbon-equivalent expression used by A516 Supplementary Requirement S54

CE = C + Mn/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15

S54 applies specifically when ordered for hydrofluoric-acid alkylation service; its CE limits are not general Grade 55 requirements. The same expression may be useful for welding assessment only when the applicable procedure or project specification adopts it.

Service-specific restrictions

A516 Grade 55 is not inherently a low-temperature-qualified plate, a hydrogen-induced-cracking-resistant plate, a sour-service grade or a plate certified for hydrofluoric-acid alkylation service. These applications require additional controls selected for the environment and construction code. Possible controls include normalized delivery, specified impact testing, hardness limits, restricted residual elements, through-thickness properties, ultrasonic examination, HIC or SSC testing, special melting or inclusion-control practices, and simulated fabrication heat treatment. Such requirements must not be inferred from the basic A516 marking.

A516 Supplementary Requirement S54 for hydrofluoric-acid alkylation service

Control	S54 requirement
Delivery condition	Normalized
Maximum CE through 1 in. [25 mm]	0.43
Maximum CE over 1 in. [25 mm]	0.45
Vanadium, heat analysis	0.02% maximum
Niobium, heat analysis	0.02% maximum
Vanadium plus niobium, heat analysis	0.03% maximum
Nickel plus copper, heat analysis	0.15% maximum
Carbon, heat analysis	0.18% minimum; maximum remains that specified for the ordered grade
Repair-weld consumables	Low-hydrogen; E60XX electrodes prohibited; resulting weld chemistry must satisfy the base-metal chemistry requirements
Identification	Additional HF-N marking

These controls apply only when S54 is explicitly specified.

Ordering and certification checklist

Information that should be resolved before purchase

Item	What to specify or verify
Specification and edition	ASTM A516/A516M-25 Grade 55 or Grade 380, or the applicable ASME SA-516/SA-516M edition for Code work.
Unit system	Use either the inch-pound grade and requirements or the SI grade and requirements consistently.
Dimensions and tolerances	Plate thickness, width, length, quantity and any special tolerances under A20/A20M.
Delivery condition	As-rolled, normalized, stress relieved, normalized and stress relieved, or another expressly permitted route.
Manufacturing route	Discrete plate or plate processed from coil; confirm the applicable testing and reporting provisions.
Impact properties	Required test temperature, absorbed energy or lateral expansion, orientation, specimen size, frequency and governing acceptance rule.
Fabrication heat cycles	Whether S3 simulated post-weld heat treatment or another representative thermal simulation is required.
Nondestructive examination	UT method, standard, acceptance level, scanning coverage and reporting requirements.
Chemistry controls	Whether product analysis, carbon-equivalent limits, residual-element limits or service-specific chemistry restrictions are required.
Certification	Heat number, plate traceability, actual heat analysis, tensile results, heat-treatment condition, supplementary test results and compliance statement.
Construction-code compatibility	Applicable code, edition and addenda; permitted material form, allowable stresses, temperature limitations and impact-test rules.
Substitution approval	Any proposed change of grade, standard, condition, thickness, manufacturing route or test basis should receive engineering approval before use.

A certificate stating only “A516 Grade 55” is insufficient for many pressure-equipment purchases. At minimum, verify the specification edition, plate identity, dimensions, heat-treatment condition, heat analysis and required mechanical-test results against the purchase order.

Selection and substitution within the A516 family

Strength levels in ASTM A516/A516M

Grade	Specified tensile strength	Minimum yield strength	Relationship to Grade 55
55	55–75 ksi [380–515 MPa]	30 ksi [205 MPa]	Lowest-strength A516 grade
60	60–80 ksi [415–550 MPa]	32 ksi [220 MPa]	Related higher-strength grade
65	65–85 ksi [450–585 MPa]	35 ksi [240 MPa]	Related higher-strength grade
70	70–90 ksi [485–620 MPa]	38 ksi [260 MPa]	Highest-strength and commonly encountered A516 grade

Higher A516 grades have different chemistry and strength requirements. They are not automatically interchangeable with Grade 55.

Substituting a higher-strength A516 grade is not simply an upgrade. It can affect forming loads, weld procedure qualification, hardness, toughness, minimum design metal temperature treatment, allowable stress, component thickness, material grouping and consistency with previously approved design documents. Likewise, a European pressure-vessel grade should not be described as equivalent merely because its nominal strength overlaps Grade 55; chemistry, impact-testing basis, thickness effects, delivery condition and certification rules must all be compared.

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Grade 380	SI grade designation within ASTM A516/A516M	Corresponds to Grade 55 when the specification is applied in the SI system; the two unit systems must be used independently.
ASME SA-516 Grade 55	ASME Boiler and Pressure Vessel Code counterpart	Use the SA specification and edition adopted by the applicable ASME Code edition. Do not assume that an ASTM-only certificate automatically satisfies Code documentation requirements.
ASTM A516 Grades 60, 65 and 70	Related grades in the same product specification	They provide progressively higher specified strength and have different chemistry limits; they are not automatic substitutes.