Scope of JIS G3115 and the SPV Series
JIS G3115 covers hot-rolled steel plates for pressure vessels operating at intermediate temperatures, and it contains six grades from SPV235 to SPV490. The letter group SPV indicates a steel plate for pressure vessel service and the number denotes the minimum yield strength in megapascals, so SPV355 is the grade specified at 355 MPa minimum yield. The standard is applied to boiler drums, pressure vessels and similar equipment where service temperatures exclude the low-temperature and elevated-temperature ranges covered by other Japanese specifications, and where good weldability and formability are required alongside strength. Plates are supplied in thicknesses from about 5 mm to 250 mm depending on the grade, in widths up to roughly 4.5 m and in lengths up to about 18 m, with full traceability from melting to dispatch.
Chemical Composition and Carbon Equivalent
SPV355 is a carbon-manganese plate steel with a low carbon content and tight limits on residual elements that would damage toughness.
| Element | C | Si | Mn | P | S |
|---|---|---|---|---|---|
| Ladle analysis, % max | 0.20 | 0.55 | 1.60 | 0.030 | 0.030 |
The combination produces a carbon equivalent value of about 0.43 for the grade, which is the basis of its good weldability without preheat in moderate thickness. Phosphorus and sulphur are held at or below 0.030 % each, which supports both toughness and resistance to hydrogen-induced cracking where the plate is used in wet hydrogen sulphide service.
Mechanical Properties by Thickness
Yield strength requirements fall as section thickness increases, because the cooling rate through the section and the amount of reduction in the mill differ. SPV355 is specified as follows.
| Thickness range | Minimum yield strength | Tensile strength | Minimum elongation |
|---|---|---|---|
| 6 mm to 50 mm | 355 MPa | 520 to 640 MPa | 19 % |
| 50 mm to 100 mm | 335 MPa | 520 to 640 MPa | per standard table for the thickness |
| 100 mm to 150 mm | 315 MPa | 520 to 640 MPa | per standard table for the thickness |
The grade is also required to demonstrate a Charpy V-notch impact energy of at least 47 J at minus 20 degrees Celsius, which is the toughness guarantee that qualifies it for pressure equipment in cold climates and for the post-weld heat treatment cycles applied during fabrication.
Delivery Conditions and Equivalent Grades
SPV355 is normally supplied as rolled, and normalization, thermomechanical control rolling or quenching and tempering can be specified by agreement where a particular toughness or heat treatment route requires it. Where comparisons are made, EN 10028-2 P355GH is the closest European grade with a similar yield and tensile band, GB/T 713 Q345R is the commonly used Chinese pressure vessel plate with a minimum yield of 345 MPa, and ASTM A516 Grade 70 is frequently quoted as an alternative although its minimum yield of 260 MPa is substantially lower, so a thickness adjustment is usually necessary when substituting it for SPV355. Grade substitutions must always be justified by the design code rather than by the grade name alone.
Forming, Welding and Heat Treatment
SPV355 forms readily by cold rolling, pressing and hot forming, and its low carbon equivalent means that preheat is not mandatory for moderate thickness in ordinary ambient conditions, although it is applied where thickness, restraint or low ambient temperature raises the risk of cracking. Shielded metal arc, submerged arc, gas metal arc and gas tungsten arc processes are all used with matching consumables, and the fabrication sequence normally allows for post-weld heat treatment where the design code requires it, with the temperature and holding time selected so that the properties achieved in the plate are retained. Edge preparation is by machining, shearing or thermal cutting with the cut edge dressed where fatigue or corrosion performance matters, and dimensional tolerances for the finished shell components follow the drawing and the applicable code.
Inspection, Certification and Supply Form
Each plate is released against ladle and product chemical analysis, tensile testing in the direction required by the order and Charpy impact testing at the specified temperature, with the number and position of test pieces taken from the standard. Ultrasonic examination to JIS G 0901 or to EN 10160 is carried out where internal soundness is a project requirement, and additional testing for hydrogen-induced cracking or sulphide stress corrosion is available for wet sour service. Plates are supplied with a mill test certificate at EN 10204 3.1, and third-party witness to 3.2 is commonly arranged for pressure equipment. Typical delivery finishes are bare, shot blasted or primed, and value-added processing such as beveling, laser cutting, drilling and post-weld heat treatment support is widely available. Each plate is marked with the grade, heat number and plate identification so that the certificate can be traced to the delivered item.
Frequently Asked Questions
Q: What does SPV355 mean?
A: The letters identify a steel plate for pressure vessel service and the number gives the minimum yield strength in megapascals. SPV355 is one of six grades in JIS G3115, ranging from SPV235 to SPV490.
Q: What is the tensile strength of SPV355?
A: The specified tensile range is 520 MPa to 640 MPa for the grade, with a minimum yield strength of 355 MPa for thicknesses up to 50 mm and lower minimum values for heavier sections.
Q: Is SPV355 the same as ASTM A516 Grade 70?
A: No. A516 Grade 70 has a minimum yield strength of 260 MPa and a tensile range of 485 MPa to 620 MPa, so it is a lower-strength plate. Substitution requires a design check, and heavier plate is often needed.
Q: Which delivery conditions are available?
A: As-rolled is standard, with normalized, thermomechanical control rolled and quenched and tempered conditions available by agreement when the design or the fabrication sequence calls for them.
Q: Is preheat needed for welding SPV355?
A: With a carbon equivalent of about 0.43, preheat is not normally required for moderate thickness under favourable conditions, but it is applied where thickness, joint restraint or low ambient temperature increases the cracking risk.
Q: What documentation accompanies SPV355 plates?
A: A mill test certificate at EN 10204 3.1 stating the chemical analysis, tensile results and Charpy impact values, plus ultrasonic examination reports where specified, and third-party inspection certificates where the purchaser requires witnessed testing.
