GB/T 713.7 06Cr18Ni11Nb S34778 Pressure Vessel Stainless Plate

06Cr18Ni11Nb S34778 is listed in GB/T 713.7-2023, the Chinese standard for pressure equipment stainless steel plate, as a titanium- or niobium-stabilized austenitic grade that resists intergranular attack after welding. As a GB/T 713.7-2023 stainless plate it is ordered by vessel and heat-exchanger shops that design to GB/T 150 and the TSG 21 safety rules, and by EPC contractors who must deliver Chinese-code equipment abroad. Its ASTM A240 347 equivalent is the nearest foreign grade by chemistry.

Reading the designation: the leading digits give the carbon level (≤ 0.08%); the element symbols that follow give the approximate contents of the main alloying elements in percent. S34778 is the unified numeric code (ISC). The grade was previously certified as GB/T 24511 S34778 until GB/T 24511-2017 was withdrawn on 1 March 2024; most chemistries carried over, but the 2023 edition revised some austenitic strength values and added impact data, so old certificates should be checked against the new tables. Older Chinese drawings may still use the former designation 0Cr18Ni11Nb. Every 06Cr18Ni11Nb pressure vessel plate is tested and certified to the 2023 edition.

SHH STEEL produces and exports stainless plate from Shanghai, works as a sales agent for mills including TISCO, Baosteel and POSCO, and runs its own processing warehouse for cutting and polishing. 06Cr18Ni11Nb is part of our GB/T 713.7-2023 pressure vessel stainless plate range; for the general-purpose version of the same grade see GB/T 4237 06Cr18Ni11Nb S34778 and for ASME projects our ASTM A240 Type 347 page.

Why designers specify S34778

Material selection for a Chinese-code pressure vessel starts with the design conditions: medium, temperature, pressure and the minimum design metal temperature. Austenitic grades such as this one are chosen when the medium needs stainless corrosion resistance and when toughness at low temperature matters, because austenite stays ductile without a transition temperature. GB/T 150 lists the permitted plate standards and allowable stresses, and the material must be supplied with a certificate that ties every plate to its heat. Because 06Cr18Ni11Nb is listed in GB/T 713.7-2023, it can be used directly under GB/T 150 without a separate material evaluation, which saves time on approvals compared with a foreign grade.

Who buys it

Our customers for this grade include pressure vessel fabricators in China and Southeast Asia, EPC contractors building Chinese-designed plants in the Middle East, Africa and Central Asia, and maintenance teams that need like-for-like replacement plate for equipment originally built to GB/T 24511 or GB/T 713.7. Export buyers often need the plate certified to GB/T 713.7 and checked against an ASTM or EN grade at the same time, which we arrange with the mill before rolling.

The table is a summary; the purchase order should cite the full standard and edition. Clause 4.2 of GB/T 713.7 requires the surface finish to be named on the order, and the edge and thickness-accuracy codes decide the tolerance class used for acceptance. For coil-cut plate, flatness and camber follow the general rules of GB/T 713.1, which every part of GB/T 713 refers to.

The S34778 chemical composition is the heat (melting) analysis the mill reports for each heat, and it must meet GB/T 713.7-2023 Table 13 in weight percent.

The product analysis is a check on the finished plate. Clause 7.2.2 of GB/T 713.7 refers to GB/T 713.1 for the permitted deviations; the values below are the customary GB/T 222 / ASTM A480 deviations applied to 06Cr18Ni11Nb and should be confirmed against the edition cited in the contract.

PREN (Cr + 3.3Mo + 16N) calculated from the minimum chemistry is 17.0. Notes in Table 13 state that some compositions were adjusted compared with GB/T 3280 and GB/T 4237, so a heat certified to GB/T 4237 does not automatically meet GB/T 713.7.

Product (check) analysis is the chemistry measured on a sample taken from the finished plate rather than from the ladle, and it is how a buyer proves the plate matches the certificate.

Under GB/T 713.7 the mill reports the heat analysis as standard. A product analysis is made when the purchase order calls for it, and the result is judged against the heat limits widened by the permitted deviations shown above. Deviations apply to one side of a range only; a heat may not exceed both the lower and upper limit of the same element. Elements marked ‘by agreement’ have no tabulated deviation and should be settled in the contract.

SHH STEEL runs positive material identification (PMI) on every plate in our Shanghai warehouse before it ships. PMI by handheld XRF confirms Cr, Ni and other alloying elements; it cannot measure carbon or nitrogen, so when low carbon matters we arrange laboratory spark-OES or combustion analysis through our steel testing service. Product analysis results are added to the 3.1 certificate or reported by the third-party inspector on a 3.2 certificate.

Sampling and acceptance

Samples for product analysis are taken across the thickness or from millings so that the result represents the whole plate, not only the surface. If a product analysis falls outside the permitted range, the usual practice under GB/T 713.1 is to retest on additional samples before the plate or batch is rejected. We keep retained samples from tested heats for a period agreed with the customer, which helps when questions arise during fabrication or inspection.

The S34778 mechanical properties are the room-temperature values that GB/T 713.7-2023 Table 16 sets for solution treated plate.

Elongation for thickness ≤ 3.00 mm is measured on A50 mm specimens per GB/T 228.1 P5. Rp1.0 is tested only when the buyer requires it in the contract. Impact energy is not a mandatory test under clause 7.4.2; it is agreed between buyer and supplier and stated in the contract, and is tested per GB/T 713.1. Design stresses are not taken from this table directly: the vessel designer uses the allowable-stress tables of GB/T 150.2, which are derived from these minimums and from the elevated-temperature data in Annex D where given.

Compared with ASTM A240 347, GB/T 713.7 sets its own strength and elongation minimums; a heat can often be dual-certified, but each certificate must state the values tested against each standard.

How designers use these values

The room-temperature minimums are the basis of the allowable stresses in GB/T 150.2. The designer takes the lower of the stress derived from tensile strength and the stress derived from proof strength, applies the code safety factors, and for elevated temperatures uses the temperature-dependent proof strength. For austenitic grades, GB/T 150 also allows a higher allowable stress at temperature where some permanent deformation is acceptable, but this is not used for flanges or parts where small deformation could cause leakage. Hardness limits on the certificate are a quick check that the plate has been correctly heat treated: a plate above the maximum hardness has usually been under-treated or cold worked.

Testing frequency

Tensile and hardness tests are made per batch as defined in the inspection rules of GB/T 713.7 clause 9 and GB/T 713.1. A batch is plate from the same heat, the same thickness and the same heat-treatment condition. When the order calls for testing of each plate or each rolled plate, state this explicitly, as it affects cost and lead time.

S34778 heat treatment solution treatment is the final heat treatment that sets the structure and properties of the plate, and GB/T 713.7-2023 Annex C gives the recommended regime for 06Cr18Ni11Nb. Mills typically solution treat this grade at about 1 000 – 1 100 °C followed by water quench or rapid cooling, so it is supplied as a solution treated stainless plate. The actual temperature and cooling method are recorded on the mill certificate.

Clause 7.1.2 allows hot-rolled strip 14.0 – 25.0 mm thick to be levelled and heat treated sheet by sheet. After heavy cold forming or hot forming of heads, the fabricator should follow GB/T 150.4 on whether re-treatment is needed; for austenitic plate this usually means a new solution treatment rather than a stress relief.

What can go wrong

An incorrectly heat-treated plate shows up as high hardness, low elongation or, in corrosion tests, as intergranular attack. Slow cooling through the sensitizing range of about 450 – 850 °C allows chromium carbides to form at grain boundaries, so cooling must be fast enough to avoid it. When we receive plate, our engineers check the heat-treatment record on the certificate against Annex C and the hardness result before releasing the material.

Sensitization is the precipitation of chromium carbides at grain boundaries between about 450 °C and 850 °C, which leaves chromium-depleted zones open to intergranular attack. 06Cr18Ni11Nb is stabilized: niobium forms its own carbides first, so chromium stays in solution even after welding or service in that range.

Welds should be made with matching stabilized filler (347-type) to keep the weld metal resistant.

Design checklist for this service

• Confirm the minimum and maximum design metal temperatures against the limits in GB/T 150 for this material.
• State on the order every test that the design relies on, because tests that are ‘by agreement’ are not performed unless they are written into the contract.
• Check that weld procedures, filler metals and any post-weld treatment are qualified for the same temperature range as the base metal.
• Keep the mill certificate, the inspection report and the weld records together in the vessel data book, as required for registration with the special-equipment authority.

A 06Cr18Ni11Nb equivalent grade is a grade in another standard with similar chemistry and properties, not an interchangeable certificate.

Equivalence is by alloy family, not certificate. Replacing S34778 with a foreign grade in a Chinese-code vessel needs approval from the designer and, where required, the special-equipment inspection authority; the reverse also applies to ASME or PED equipment built from GB/T plate.

Welding of 06Cr18Ni11Nb is done by GTAW, SMAW, GMAW or SAW with 347-type filler metal. No preheat is needed; keep interpass temperature below about 150 °C and heat input moderate to limit distortion and hot cracking. Pickle and passivate welds for corrosive service.

Weld procedures are qualified to NB/T 47014 for Chinese-code equipment, or to ASME IX for export projects. Cold forming of heads and shells is normal for this grade; austenitic plate work-hardens quickly, so press capacity must allow for it. Plasma, laser and waterjet cutting are all suitable; remove heat-tinted edges before welding.

Practical welding notes

• Clean the joint area with stainless-only brushes and solvent; carbon steel contamination causes rust spots.
• Back purge with argon on root passes to avoid oxidized roots.
• Control ferrite in austenitic weld metal (typically a few percent) to avoid hot cracking, except where fully austenitic weld metal is required for corrosion or cryogenic reasons.
• Post-weld heat treatment is not normally required; where the code calls for it, discuss the effect on sensitization with the designer.

Our warehouse can supply bevelled edges and cut blanks ready for welding, which reduces work in the fabrication shop.

Corrosion resistance of 06Cr18Ni11Nb is set by its chromium content: it resists intergranular attack after welding or service between 450 °C and 850 °C because of stabilization. Its minimum PREN is 17.0.

For welded parts in sensitizing media, an intergranular corrosion test to GB/T 4334 can be ordered. Austenitic grades of this class are susceptible to chloride stress-corrosion cracking above about 60 °C; where that risk exists, duplex grades are often preferred. Hydrotest water chloride content should be controlled as required by GB/T 150.4.

Media guide

The table is general guidance. Final material selection should be based on the actual medium, temperature and concentration, and where possible on plant experience or corrosion testing.

Applications of 06Cr18Ni11Nb follow from its corrosion and temperature behaviour as a pressure equipment stainless steel plate. Typical uses:

• Equipment operating between 450 °C and 850 °C
• Exhaust and heater parts
• Refinery vessels in polythionic-acid risk zones
• Chemical plant shells

Buyers specifying 06Cr18Ni11Nb for these jobs often compare it with GB/T 713.7 06Cr18Ni11Ti S32168 and GB/T 713.7 07Cr18Ni11Nb S34779; the comparison table on this page shows the differences.

Other GB/T 713.7 grades buyers request alongside it: GB/T 713.7 022Cr19Ni10 S30403.

Selection guidance by application

For storage tanks and low-pressure vessels the decision is usually driven by corrosion resistance and cost, and the plate thickness is moderate. For high-pressure or large-diameter vessels, strength becomes important and nitrogen-bearing or duplex grades can reduce wall thickness. For heat exchangers the tube sheets, shells and channels often use different grades, and we can supply all of them in one order with consistent certification.

On S34778 vs 347, the alloy family is the same, but GB/T 713.7 sets its own chemistry limits and strength minimums. The table compares the grades buyers most often weigh it against, using GB/T 713.7-2023 values.

How to choose

Start from the corrosion requirement and the design temperature, then compare strength, availability and cost. A higher-alloy grade is only worth its price when the medium or temperature needs it; a lower-alloy grade that is readily available often gives a shorter lead time. Low-carbon and stabilized grades are preferred for welded parts in corrosive media, nitrogen-bearing grades when strength saves wall thickness, and H-grades only where creep governs. Our engineers can review your design conditions and suggest the most economical grade that meets the code.

Weight example: a 10 mm plate at 7.9 – 8.0 g/cm³ weighs about 79 – 80 kg/m². Ask for cut-to-size blanks to reduce scrap on heads and shells.

Tolerance and flatness notes

PT.A is the normal thickness accuracy class; PT.B gives a tighter tolerance and is useful when the designer has little corrosion allowance or when plates are rolled into shells with close fit-up requirements. Flatness depends on thickness and width, and cut-to-length plate from coil is usually flatter than as-rolled thick plate. For heads and dished ends, ask us for circular blanks cut to the developed diameter, which reduces handling and scrap at the fabricator.

We offer steel cutting services and stainless surface finishing services in our Shanghai warehouse.

Choosing a finish

No.1 is the standard finish for hot-rolled pressure vessel plate; it is suitable for shells, heads and parts that will be pickled or machined after fabrication. Cold-rolled 2B is used for thin vessels, liners and parts where a smoother surface helps cleaning. Polished finishes are specified for hygienic vessels in food and pharmaceutical plants, where surface roughness limits are part of the design. Plates can be supplied with PE film protection to prevent scratching during fabrication.

• Heat chemical analysis on every heat; product analysis by agreement
• Tensile test and hardness per Table 16
• Impact test by agreement
• Intergranular corrosion (GB/T 4334) and UT on request
• 100% PMI and dimensional check by SHH STEEL
• EN 10204 3.1 certificate; 3.2 with SGS, BV, TUV or a named inspector

Every test result appears on the certificate with the heat number, so the plate can be traced from mill to finished vessel.

Third-party inspection

For export projects, a 3.2 certificate is often required. In that case an independent inspector witnesses sampling and testing at the mill and countersigns the certificate. We coordinate SGS, BV, TUV, Lloyd’s or a client-named inspector, and we schedule witness points so that inspection does not delay rolling. In our warehouse we check dimensions, flatness, surface condition and marking, and repeat PMI on each plate before packing.

• Standard and edition: GB/T 713.7-2023
• Grade and code: 06Cr18Ni11Nb / S34778
• Thickness, width, length and quantity
• Edge EC or EM; thickness accuracy PT.A or PT.B
• Surface finish (clause 4.2)
• Extra tests: impact temperature, IGC, UT, product analysis
• Certificate type: EN 10204 3.1 or 3.2

Send the list to SHH STEEL and we return a quotation with mill, lead time and stock options.

Common ordering mistakes

• Citing GB/T 24511 instead of GB/T 713.7-2023 on new orders.
• Leaving out the surface finish, which clause 4.2 requires.
• Not stating impact test temperature when the design needs it.
• Ordering to GB/T 4237 for pressure parts; GB/T 4237 plate is not certified for pressure equipment.

A short technical review before order placement avoids these problems, and our engineering team does this free of charge.

06Cr18Ni11Nb is produced by a smaller number of Chinese mills; we place mill orders through the producers we represent and confirm minimum quantities per thickness. Lead time is typically 30-40 days for mill production (production can be scheduled within 30-40 days), and we confirm the rolling slot with the quotation.

Buyers who normally purchase 347 stainless steel plate to ASTM A240 can source this grade through the same mills, with the certificate issued to GB/T 713.7-2023.

Every plate is traceable to its heat number, and copies of the mill certificates stay on file for repeat orders and audits. The same mills also supply our ASTM A240 Type 347 plate, so mixed-standard orders can ship together.

Packing and export documents

Plates are packed on steel or fumigated wooden pallets with waterproof wrapping, edge protectors and steel straps, and each bundle carries labels with grade, standard, heat number, size and weight. Export documents include the commercial invoice, packing list, mill certificates, certificate of origin and, when required, inspection certificates. We ship from Shanghai port in containers or break bulk, and can consolidate mixed grades in one shipment.

GB/T 713.7 06Cr18Ni11Nb (S34778) is an austenitic pressure-vessel plate grade, known internationally as 347. It is defined by Table 13 chemistry (C ≤ 0.08, Cr 17.00 – 19.00, Ni 9.00 – 12.00, Nb 10×C – 1.00) and Table 16 properties of Rp0.2 ≥205 MPa, Rm ≥ 515 MPa and A ≥40%. Typical uses include equipment operating between 450 °C and 850 °C, exhaust and heater parts and refinery vessels in polythionic-acid risk zones.

Before ordering, state the standard edition, the grade name with its code, and any extra tests, so that the mill certificate matches your design documents. SHH STEEL supplies 06Cr18Ni11Nb plate from stock and by mill order, cut to size and finished in our own warehouse, with EN 10204 3.1 certificates. For related grades see GB/T 713.7 06Cr18Ni11Ti S32168 and GB/T 713.7 07Cr18Ni11Nb S34779, our GB/T 713.7-2023 category, the ASTM A240 Type 347 page and GB/T 4237 06Cr18Ni11Nb S34778. Send your sizes and quantities for a quotation.