Carbon steel plate is the normal product form for pressure-vessel shells, heads, and other welded sections, while carbon steel pipe serves mainly tubular connections and heat-exchanger internals [S1][S5].
The choice must follow design pressure, service temperature, corrosion exposure, thickness, fabrication method, impact requirements, and the applicable vessel code rather than the words carbon steel alone [S1][S4].
Plate-versus-pipe function and scope
Pressure-vessel plate is supplied in defined grades, thicknesses, delivery conditions, and heat treatments, and it is formed into shells, heads, and flat pressure-retaining components through cutting, rolling, welding, and, where required, heat treatment [S1][S5]. A grade such as ASTM A516 Grade 70 identifies a carbon-manganese plate material, not the allowable pressure of the finished vessel [S4].
Pipe has a different fabrication geometry. It is commonly used for vessel connections and heat-exchanger tubes, and can be produced as seamless or longitudinally rolled pipe [S5]. A welded vessel shell is not automatically a pipe application, because the shell must satisfy the vessel design, material specification, weld procedure, inspection, and forming requirements as an integrated pressure boundary [S1][S4].
For procurement, specify carbon steel plate by grade, thickness, heat treatment, impact condition, inspection class, and certificate requirement. Specify carbon steel pipe separately by grade, outside diameter, wall thickness, length, manufacturing method, end condition, and the pressure-boundary role. Plate-thickness tolerances also affect forming and fit-up, as detailed in Carbon Steel Plate Thickness Tolerances for Fabrication.
Grade options by pressure and temperature
ASTM A516 Grade 70 is a common pressure-vessel plate specification with a minimum yield strength of 260 MPa, tensile strength of 485–620 MPa, elongation of at least 21%, and 27 J impact capability at -20°C; its listed maximum service temperature is 455°C [S3]. These values describe the plate grade, not the allowable stress of a finished vessel, which also depends on the governing design code, thickness, and inspection requirements [S3][S4].
For lower-temperature applications, ASTM A285 Grade C is listed with minimum yield strength of 205 MPa, tensile strength of 380–515 MPa, elongation of at least 20%, and a 400°C maximum service temperature [S3]. For elevated-temperature service, ASTM A387 Grade 11 is listed with minimum yield strength of 275 MPa, tensile strength of 485–620 MPa, elongation of at least 20%, and a 600°C maximum service temperature [S3].
EN and GB alternatives include P265GH and Q345R for A516 Grade 70, P245GH and Q245R for A516 Grade 60, and 16Mo3 and 12CrMoG for A387 Grade 11 [S3]. Equivalent designations are not automatically interchangeable: impact testing, heat-treatment condition, certification, and product-form requirements still require verification [S3].
Decision criteria: shell, tube, or connection
Plate wins for the main shell when the vessel requires large rolled cylinders, dished heads, transition sections, or substantial nozz reinforcement. Pipe wins where the pressure boundary is tubular, such as exchanger tubes, dip tubes, standpipes, or a vessel connection [S5]. The steel plate route supports broad dimensional availability, including typical carbon-steel plate thickness from 0.4 mm to 80 mm, widths from 1,000 mm to 45,000 mm, and lengths up to 18 m [S2].
Cost cannot be compared by product form alone. Carbon steel is less expensive than stainless steel or specialty alloys, but the relevant comparison includes rolling or forming, seam welding, heat treatment, nondestructive examination, corrosion protection, and fabrication labor [S6][S7]. Plate is usually the efficient choice for primary shells because forming a large vessel from flat product allows the manufacturer to control geometry and joints; pipe becomes economical when the required component is already tubular and its qualified specification matches the service [S5].
For corrosion service, low-carbon grades provide better weldability and formability, with the cited low-carbon range at 0.06%–0.25% carbon versus 0.25%–0.55% for medium-carbon and 0.55%–1.0% for high-carbon plate [S2]. The pressure-vessel grade should therefore be selected by specification and design checks, not simply by picking a lower carbon number.
Welding, inspection, and delivery constraints
Shell fabrication typically involves cutting, rolling, welding, and sometimes heat treatment, with the weld procedure, heat-input controls, and inspection class tied to the governing design [S1][S5]. Pipe used in pressure service also needs qualification for its manufacturing method, dimensions, material, and welding or heat-treatment condition [S3]. The material designation alone does not establish code compliance.
Impact requirements can control grade selection. A516 Grade 70 carries a cited 27 J requirement at -20°C, while A516 Grade 60 has the same stated impact requirement and an indicated maximum service temperature of 455°C [S3]. For projects under PED, the supplied comparison identifies P265GH and P355GH as common EN 10028-2 grades, while ASTM-oriented projects commonly specify A516 and A285 plate [S3].
For sour service involving H2S, the material basis must also address hydrogen-induced cracking resistance. HIC-resistant pressure-vessel plate is available under the NACE framework, with NACE MR0175 identified for the sour-service selection [S1]. This requirement must be written into the plate specification, rather than assumed from a generic carbon-steel grade.
Corrosion limits and practical failure modes
Carbon steel is economical when corrosion is predictable and manageable, but it does not provide the corrosion resistance associated with stainless steel or duplex stainless steel [S4][S6]. The service basis must record normal operation, startup, shutdown, cleaning, draining, and credible upset conditions, including wet condensate, deposits, and stagnant zones that can create exposure beyond the nominal bulk-fluid condition [S4].
The main failure mode is not simply uniform section loss. Local corrosion beneath deposits, chloride-bearing rinse water, external washdown, jacket leakage, and wet insulation can attack the shell from different service positions [S4]. Mitigation may include coating, lining, inhibitors, control of oxygen and water, corrosion allowance, or a change to a higher-alloy material, but each measure belongs in the design basis and inspection plan [S4][S7].
Carbon content creates a fabrication trade-off. As carbon rises from 0.25% to 1.0%, plate generally gains hardness and strength while losing weldability and formability [S2]. Vessel fabricators therefore cannot accept a generic substitution without checking carbon, manganese, silicon, phosphorus, sulfur, mechanical properties, heat treatment, and thickness limits [S2][S4].
Procurement and code compliance
The purchase specification should connect grade to product form and delivery state. For ASTM-oriented supply, A516 Grade 70, A285 Grade C, and A537 Class 1 or Class 2 are identified as common vessel plate choices [S1]. For EN-oriented supply, EN 10028-2 grades include P265GH, P355GH, 16Mo3, and 13CrMo4-5; GB 713 includes Q245R, Q345R, and 16MnDR [S3].
Traceability should cover the material grade, plate thickness, heat number, chemical and mechanical results, impact requirement, heat-treatment condition, and inspection certification. The comparison specifically flags EN 10204 3.1 certification and the need to verify equivalent-grade impact, heat treatment, and certification requirements [S3]. For pipe, add outside diameter, wall thickness, manufacturing method, length, and end preparation to the same package [S5].
Final approval belongs to the designer and authorized fabricator. The defensible choice is A516-type plate for a conventional shell, A285 plate for lower-temperature or lower-pressure service where its properties are adequate, A387 or another alloy grade for elevated-temperature service, and qualified pipe for tubular internals or connections [S3][S4][S5]. The material order should not be released until product form, operating envelope, corrosion basis, weld method, impact test, heat treatment, and code certification all match.