Why procurement teams confuse the two

Every few weeks, a procurement manager at a chemical EPC sends a request that reads, in effect: "Send us Grade 2 titanium bar per ASTM B348, we need it for a pressure vessel." The mill replies, the material arrives with an ASTM B348 test report, and three weeks later the Authorized Inspector refuses to sign off on the weld procedure qualification because the bar was not certified to ASME SB348.

The same procurement group is rarely confused on purpose. They confuse the two because on paper, ASTM B348 and ASME SB348 are nearly the same document. SB348 was adopted into the ASME Boiler and Pressure Vessel Code as a "S" specification, which means ASME lifted the text of B348, made formatting edits, and republished it as Section II, Part B. The chemistry tables, the tensile requirements, the grade definitions — these do not change between the two.

What does change is the role the document plays once your project enters ASME code jurisdiction. That is where most purchasing mistakes are made, and it is the difference this article is built to explain.

Scope: what each standard actually covers

ASTM B348 — Standard Specification for Titanium and Titanium Alloy Bars and Billets

B348 covers ten grades of unalloyed titanium (Grades 1–4, 7, 11, 16, 17, 26, 27) and eleven titanium alloy grades (Grades 5, 9, 12, 19, 23, 28, 29, and so on) in bar and billet form. It defines:

• Chemical composition limits for each grade

• Tensile, yield, and elongation requirements

• Bend test requirements for certain grades

• Mill product form (hot-finished, cold-finished, annealed, solution-treated)

• Marking, packaging, and the standard MTR format

B348 is a material purchase specification. It tells the mill what to make and how to test it. It does not, by itself, authorize use in any specific code-stamped equipment.

ASME SB348 — ASME Boiler and Pressure Vessel Code, Section II, Part B

SB348 carries the same ten unalloyed and eleven alloy grades, the same chemistry, and the same mechanical property tables as B348. Where it adds content:

• Mandatory ASME marking on the bar or its bundle — name, grade, condition, manufacturer identifier, and the SB348 designation

• Certified Material Test Report (CMTR) format compatible with ASME Section II, Part A reporting requirements

• Acceptance into ASME code-stamped assemblies — Section VIII (pressure vessels), Section III (nuclear), Section XII (transport tanks), and the B31 piping codes

• Authorized Inspector (AI) sign-off — the AI must be able to trace the heat, the lot, and the test report back to a manufacturer on the ASME QSC-300 list

The key practical point: SB348 is what allows the bar to legally enter a code-stamped weld. B348 does not.

Chemistry and grades: where they are identical

To dispel the most common procurement misconception directly: the chemical composition limits are not different between B348 and SB348. A Grade 2 bar made to either specification has the same Fe, O, N, C, H, and residual limits, the same tensile range (345 MPa min UTS for Grade 2), and the same elongation minimum (20%).

What the procurement office sometimes gets wrong is assuming the mill can switch from B348 to SB348 at the touch of a button. In practice, most major titanium mills — including the integrated producers in Baoji, Sheffield, and the U.S. — hold dual certification on the same heat. The bar is rolled once, tested once, and the heat record is then issued as either B348, SB348, or both, depending on what the order specifies.

For grade selection on pressure vessel work, three grades dominate:

• Grade 2 — the workhorse unalloyed grade. Used in shell and tube heat exchangers where the design temperature stays below ~150 °C and chloride pitting is not the controlling corrosion mechanism.

• Grade 7 — Grade 2 with 0.12–0.25% Pd added. Used in reducing acid environments (HCl, dilute H₂SO₄) where unalloyed titanium would otherwise suffer general or pitting attack.

• Grade 12 — Ti-0.3Mo-0.8Ni. Used in hot chloride solutions and wet chlorine service, especially in chlor-alkali and desalination preheaters. Often paired with Grade 7 depending on the corrosion profile.

Mechanical and supplementary testing

For routine bar orders, the standard test envelope is identical under both specifications:

• Chemical analysis per heat

• Tensile test per lot (or per heat, depending on size)

• Bend test for cold-worked bar where required by the grade

• Hardness survey on heat-treated alloys

The divergence appears in three additional testing categories that code work pulls in:

Hydrostatic and pressure-decay testing

Neither B348 nor SB348 mandates a hydrostatic test on the bar itself. The hydrostatic test requirement lives with the fabricated vessel, not the raw stock. However, when a vessel fabricator is qualifying a new bar source, they often request a hydrostatic test on a sample forging or a section of bar to verify internal soundness — this is a fabricator-level requirement, not a specification requirement.

Impact testing

For low-temperature service below −29 °C (−20 °F), Section VIII requires Charpy V-notch impact testing. SB348 does not require impact testing by default; the requirement is added by the design code at the vessel level. If you order bar without impact testing and your vessel design later requires it, you are looking at either re-test from a reserve sample (often unavailable) or replacement order.

This is one of the most common late-stage surprises in cold-service titanium vessel work.

Intergranular corrosion and alpha case

Neither specification includes an intergranular corrosion test. However, for service in aggressive chloride environments, fabricators often request metallographic evaluation of the bar cross-section for alpha case — the oxygen-rich brittle layer introduced during hot working. A 25–75 µm alpha case is generally acceptable; above 100 µm it should be removed by machining or chemical milling before the bar enters fabrication.

Certification format and traceability

This is where the difference becomes operational rather than documentary. The same heat of titanium can carry three different certification envelopes, and the receiving inspector will treat each one differently.

ASTM B348 MTR

A typical B348 Mill Test Report carries:

• Heat number and chemistry

• Mechanical property results

• Manufacturer address

• Statement of compliance to B348

• Signature of the mill's quality representative

For non-code industrial service — a chemical plant's internal pipe rack, a structural bracket, a machined fastener — this is sufficient. Most receiving departments accept it without further review.

ASME SB348 CMTR

An SB348 Certified Material Test Report adds:

• Heat number, chemistry, and mechanical results (same content as B348)

• Explicit reference to ASME SB348 and the applicable edition (typically the edition referenced in the project design code)

• Marking verification statement — that the bar was marked per the ASME format at the mill

• Manufacturer's ASME certification number (where the mill holds an ASME QSC-300 certificate)

• Reference to Section II, Part A reporting requirements

The Authorized Inspector at the vessel fabricator will read the SB348 CMTR line by line. If the ASME certification number is missing, or if the manufacturer is not on the QSC-300 list, the material is rejected at receiving — even if the chemistry and mechanical results are perfect.

Dual certification

Most major titanium mills hold dual certification on the same heat: B348 + SB348 stamped simultaneously, with a single CMTR that references both. For projects that may eventually transition from non-code to code service — common in chemical EPC where the same heat ends up split between process piping and a pressure vessel — dual certification eliminates the reorder risk.

EN 10204 3.1 / 3.2 — the European angle

European pressure equipment under the PED (Pressure Equipment Directive) does not use ASME SB348 directly. Instead, it accepts material per EN 10204 3.1 or 3.2 certification referencing the European material designations (e.g., Ti Grade 2 / W.Nr. 3.7035). If your customer is in the EU and the vessel is CE-marked, the receiving department will look for a 3.1 or 3.2 certificate — not an SB348 CMTR. The chemistry and properties are equivalent, but the certification format is different. Some mills will issue a "triple certification" package: B348 + SB348 + EN 10204 3.1 on a single heat.

Which one your pressure vessel inspector will accept

For any vessel designed to ASME Section VIII (Divisions 1 or 2), the bar must be SB348-certified and the manufacturer must be on the ASME QSC-300 list at the time the material is produced. This is the bright line.

What happens when a fabricator tries to substitute B348 for SB348 on a code vessel:

1. The Authorized Inspector reviews the CMTR at receiving.

2. If the cert references B348 only, the AI flags the material as not ASME-accepted.

3. The fabricator has three options: (a) scrap and reorder, (b) request the mill to reissue the cert as SB348 if dual-certified on the original heat, or (c) submit a request for Case-by-Case approval to the ASME Code Committee.

4. Option (a) is expensive — weeks of delay and the cost of the original heat. Option (b) is viable only if the heat was originally dual-certified. Option (c) is theoretically possible but rarely granted for a simple spec substitution.

The right time to decide between B348 and SB348 is at the RFQ stage, before the purchase order is issued. By the time the heat is rolled, the certification choice is fixed.

B31.3 process piping: a separate decision

Process piping designed to ASME B31.3 does not use Section VIII acceptance. Instead, B31.3 has its own table of acceptable materials (Table A-1 for ferrous and non-ferrous, with Section A-330 covering titanium specifically). For titanium bar used as piping stock — for example, a forged branch connection or a reinforcement pad — B31.3 accepts material that meets an ASME specification listed in the table, which for titanium bar is SB348.

The practical implication: even though B31.3 is not a vessel code, the material specification reference still goes through SB348. There is no B31.3 "fast track" that allows B348-only titanium in code piping.

For B31.3 welded pipe, the analogous specification is SB861 (seamless) or SB862 (welded). For B31.3 plate, it is SB265. For B31.3 fittings, it is SB363. The same logic applies: each product form has its own SB-numbered specification, and B-numbered ASTM specs are not accepted as direct substitutes.

A real receiving floor case

The following is a composite of actual receiving inspection issues seen at chemical EPC fabrication shops — details adjusted, but the failure mode is representative.

Scenario

A mid-sized EPC was building two titanium shell-and-tube heat exchangers for a chlor-alkali plant. The vessel design was Section VIII Division 1, U-stamp, with Grade 2 tubesheet forgings and Grade 7 tubes. Tubesheet stock was ordered as 250 mm bar, 4 heats, intended for SB348 supply. The purchase order specified "ASTM B348 / ASME SB348 dual certified."

What went wrong

The mill shipped the bar with a CMTR referencing only B348. The mill's quality department had checked the chemistry and mechanicals against both specifications, but the certification text referenced B348 alone — apparently a clerical issue in the mill's QMS, traced back to a 2023 update of the mill's document template. The heat was technically dual-capable, but the paperwork was single-spec.

What the AI did

The Authorized Inspector refused to release the heats. The fabricator had two options: scrap and reorder, or request a reissued CMTR from the mill. The mill agreed to reissue — taking nine business days — but the fabrication schedule was already two weeks behind. The tubesheet machining sequence had to be re-sequenced.

What it cost

Estimate from the fabricator's project controls team:

• Nine business days of schedule slip on the exchanger package — roughly $45,000 in field erection delay costs.

• CMTR reissuance fee from the mill — $1,200 per heat, $4,800 total.

• Internal non-conformance report processing — about 30 engineering hours.

What it would have cost to prevent

A pre-production quality planning meeting between the EPC, the fabricator, and the mill — one hour of phone time, a checklist confirming dual-cert intent at the PO level, and a request for a sample CMTR before rolling. Estimated cost: zero, beyond the hour of coordination time.

The bar was perfect. The paperwork was the problem. This is what most titanium pressure vessel supply failures look like.

Procurement specification checklist

Before issuing a titanium bar purchase order for any pressure-bound equipment, the following items should be confirmed in the specification. This is the minimum set; project-specific requirements (NDE, PMI, additional mechanical tests) are layered on top.

Specification checklist

1. Specification: ASTM B348, ASME SB348, or dual certification. Default for code work: dual.

2. Grade: Grade 1, 2, 7, 12, or as required by corrosion evaluation. State the UNS number (R50400 for Gr2, R52400 for Gr7, R53400 for Gr12) to eliminate ambiguity.

3. Product form: Hot-finished bar, cold-finished bar, annealed, solution-treated. State condition per ASTM B348 Section 6.

4. Diameter range and tolerance: Specify the diameter and the tolerance class per B348 Table 4 (for hot-worked) or Table 5 (for cold-worked).

5. Length and straightness: State random lengths vs. specified lengths, and straightness tolerance.

6. Surface condition: Pickled, ground, turned, as-rolled. State roughness where it matters for subsequent machining or welding.

7. Mechanical test requirements: Tensile per heat/lot, impact if low-temperature service is anticipated, hardness for heat-treated alloys.

8. Supplementary tests: Alpha case evaluation, intergranular corrosion test, ultrasonic examination per ASTM B548 if specified.

9. Certification format: ASTM A1058 MTR, ASME CMTR, EN 10204 3.1 or 3.2, or combination. State the required format explicitly.

10. Manufacturer qualification: For SB348 supply, confirm the mill holds an active ASME QSC-300 certificate. For PED supply, confirm the mill can issue EN 10204 3.1 or 3.2.

11. Marking requirements: State marking format — ink stamp, laser etch, tag, or combination — and whether the ASME stamp is required on each bar or on the bundle.

12. Traceability: Heat number traceability from CMTR to bar, including transfer markings if the bar is cut downstream.

13. Packaging and export: For ocean freight, specify seaworthy packaging, desiccant, and wood compliance (ISPM 15 for international shipments).

Frequently asked questions

Can a bar certified to ASTM B348 be used in an ASME Section VIII pressure vessel?

Not directly. ASTM B348 certifies the material chemistry and mechanical properties only. For Section VIII construction, the bar must be supplied as ASME SB348 — which adds the ASME marking, certified mill test report format, and (where required) traceability under Section II, Part A. Using B348 without SB348 dual-certification typically results in the Authorized Inspector rejecting the material at receiving.

Is the chemistry different between B348 and SB348?

No. SB348 is the ASME adoption of B348 — the chemical composition limits, mechanical property ranges, and grade definitions are identical. The difference is in certification format, traceability, marking requirements, and acceptance into ASME code-stamped assemblies.

Do I need SB348 if my pressure vessel is only designed to ASME B31.3?

B31.3 (Process Piping) accepts materials per the ASME B31.3 tables, which reference SB-numbered specifications. For titanium, this typically means SB348 for bars and SB861 for welded pipe. B348-only material generally cannot be used in B31.3 piping without a Case-by-Case approval.

Does the European PED accept ASME SB348?

PED requires CE-marking of pressure equipment and the material is typically accepted via EN 10204 3.1 or 3.2 certification referencing European designations (e.g., W.Nr. 3.7035 for Grade 2). SB348 is technically a non-European designation. In practice, European fabricators request the mill issue dual certification: SB348 for the design reference and 3.1/3.2 for the PED acceptance. Most major titanium mills can issue both on a single heat.

What grades of SB348 are most common for pressure vessel tubesheets?

Grade 2 dominates for non-corrosive service. Grade 7 (with palladium) for reducing acid service. Grade 12 (Ti-0.3Mo-0.8Ni) for hot chloride and wet chlorine. For tubesheet forgings specifically, the bar is often rolled to a larger diameter than the finished forging, then machined down — this allows the mill to supply larger bar diameters that may not be available in the final forging form.

How long does dual certification (B348 + SB348) take compared to B348-only?

At the mill level, dual certification adds no time to the production schedule because the same heat, the same tests, and the same production run are used. The only added time is in the documentation stage, typically 1–2 business days for the mill to issue the dual CMTR. For a routine order, expect 1–2 weeks additional lead time compared to B348-only, mostly driven by the mill's documentation queue.