ASME B16.5 Flange Rating Calculator (Pressure–Temperature)

Returns the working-pressure rating of a flange — its allowable pressure at your design temperature — from the ASME B16.5-2017 pressure–temperature tables for material Groups 1.1 (carbon steel), 2.1 (304), 2.2 (316/317) and 2.3 (304L/316L), Classes 150 through 2500, with linear interpolation between listed temperatures as B16.5 Section 2 permits. Enter a design pressure and it becomes a PASS/FAIL rating screen.

Method last updated 2026-07-31 (calculation changelog) · fixture-verified on every build — most recently 2026-09-14.

Built and fixture-verified by Matthew Norris, P.E. — active P.E. licensure in Arizona, California, Kansas, Missouri, North Carolina, Texas.

Answers the everyday question “what is this flange good for at temperature?” The rating is a property of the flange's material group and class — an A106 Gr B line is normally flanged with A105 forgings, which is Group 1.1. Unlike most of this site, the rating values here are not computed from an equation: they are the B16.5-2017 table values themselves, embedded and fixture-locked, cited to the table and row they came from. B16.47 large-diameter flanges are deliberately out of scope. This page documents the retired 2017 edition; the current B16.5-2025 tables are embedded and drive the rating derivation inside PiperFLG (Pro Plus), with 2017 selectable there — 68 of 511 cells changed between editions, all within Groups 2.1/2.2.

Method

The lookup reads the B16.5-2017 U.S.-customary rating tables (Mandatory Appendix II) for the selected material group and class:

rating(T) = table value at T, or linear interpolation between the bracketing rows:
P(T) = P_lo + (T − T_lo)/(T_hi − T_lo) · (P_hi − P_lo)

utilization = P_design / rating    status = PASS if utilization ≤ 1

The −20-to-100°F row applies flat for T ≤ 100°F. Where the table shows no value — Class 150 above 1,000°F for the stainless groups, or any temperature above a group's last row — the flange is not rated and the check fails. Material sub-limits inside a group (A537 Cl.1 ≤700°F, A351 CF3 ≤800°F, 304L ≤800°F, the ≥0.04% carbon requirement above 1,000°F, the >800°F graphitization advisory for carbon steel) surface as warnings at the relevant temperatures.

Limitations — what this calculator is not

• ASME B16.5 covers NPS 1/2 through NPS 24 — larger flanges are B16.47, which this calculator deliberately does not include.
• The group is the flange material's, not the pipe's — check the flange spec against B16.5 Table 1A (A106 Gr B pipe is typically flanged with Group 1.1 A105 forgings).
• Ratings assume the joint is made per the Code: gasket and bolting per B16.5, no external piping moments — screen external F and M with the flange equivalent pressure calculator.
• Four material groups are embedded (1.1, 2.1, 2.2, 2.3). Other groups exist in B16.5; they are not yet included here.
• Low-temperature service below −20°F invokes the construction code's impact/MDMT rules — the rating alone is not sufficient.

Quick reference — Group 1.1 (carbon steel) ratings, psig

The full B16.5-2017 pressure–temperature table for Group 1.1 (A105, A350 LF2, A216 WCB and friends — the group most process flanges live in). Values are working pressure in psig; the first row covers −20°F to 100°F.

Class 150 & 300 at a glance — all four embedded groups

Reading it: carbon steel (1.1) out-rates the stainless groups at low temperature, the standard austenitic grades (2.1/2.2) hold their rating far better with heat, and the L-grades (2.3) trade rating for corrosion/weldability everywhere. Between listed temperatures, interpolate — or open the calculator and let it screen your design pressure with the group's material warnings applied.

Worked example — fixture-verified

A Class 300, Group 1.1 (A105) flange on a hot-oil line at 450°F design, 500 psig design pressure. 450°F falls between table rows, so the rating is interpolated.

Step by step

1. Bracket the temperature: the Group 1.1 Class 300 table gives 635 psig at 400°F and 605 psig at 500°F.
2. Interpolate linearly (B16.5 Section 2): P = 635 + (450−400)/(500−400) · (605−635) = 635 − 15 = 620 psig.
3. Screen the design pressure: utilization = 500 / 620 = 0.81 ≤ 1.

The flange is adequate for pressure–temperature. External bending moment or axial pull from the piping would consume margin — screen those with the Kellogg equivalent-pressure check against this same 620 psig rating.

Hygienic skid — Group 2.3 (316L) Class 150 at 250°F

A 316L Class 150 flange on a clean-utility line at 250°F (SIP conditions). L-grade stainless is Group 2.3 — rated lower than standard grades, which is exactly why the group matters.

Step by step

1. Bracket: Group 2.3 Class 150 gives 195 psig at 200°F and 175 psig at 300°F.
2. Interpolate: P = 195 + (250−200)/(300−200) · (175−195) = 195 − 10 = 185 psig.

Note the gap to Group 2.2: a standard-grade 316 flange at the same conditions rates 225 psig (235→215 interpolated) — specifying L-grade costs real rating margin at temperature.

Fixture case “Group 2.3 Class 150 at 250F -> 185 psig by interpolation (hygienic CIP-adjacent case)” (tolerance 0.001) — locked in the same release gate as the example above.

Additional verified cases in this fixture

input:  {"group":"1.1","flangeClass":"150","T":100}
expect: {"rating":285}
tol:    1e-9

input:  {"group":"1.1","flangeClass":"150","T":125}
expect: {"rating":278.8}
tol:    0.001

input:  {"group":"2.1","flangeClass":"150","T":1100,"Pdesign":50}
tol:    1e-9

input:  {"group":"2.3","flangeClass":"600","T":850,"Pdesign":700}
expect: {"rating":675,"utilization":1.037}
tol:    0.001

input:  {"group":"2.2","flangeClass":"2500","T":100,"Pdesign":5000}
expect: {"rating":6000,"utilization":0.8333}
tol:    0.001

input:  {"group":"1.1","flangeClass":"2500","T":1000}
expect: {"rating":715}
tol:    1e-9

input:  {"group":"2.1","flangeClass":"300","T":1500,"edition":"2025"}
expect: {"rating":50,"basis":"ASME B16.5-2025, Table 2-2.1C — row 1500°F"}
tol:    1e-9

input:  {"group":"1.1","flangeClass":"600","T":1000,"edition":"2025"}
expect: {"rating":170,"basis":"ASME B16.5-2025, Table 2-1.1C — row 1000°F"}
tol:    1e-9

input:  {"group":"2.1","flangeClass":"300","T":1425,"edition":"2025"}
expect: {"rating":70,"basis":"ASME B16.5-2025, Table 2-2.1C — linear interpolation 1400→1450°F (80→60 psig), per B16.5 Section 2"}
tol:    1e-9

Sources & citations

• ASME B16.5-2017, Mandatory Appendix II, Tables II-2-1.1 / II-2-2.1 / II-2-2.2 / II-2-2.3 (psig/°F) — rating values embedded and fixture-locked
• ASME B16.5-2017, Table 1A — material specification to group assignments
• ASME B16.5-2017, Section 2 — pressure–temperature ratings and interpolation

Per the source & citation policy, allowable-stress and factor table values are inputs — typed from your governing edition, or autofilled on paid tiers from the embedded datasets enumerated there, always cited by standard, edition, table and line. Where a page does reproduce specific ASME data (the B16.5 ratings, the quick-reference tables), it states the source table and conditions inline.

FAQ

Is linear interpolation between table temperatures allowed?

Yes — B16.5 Section 2 permits linear interpolation between listed temperatures. The calculator does it for you and reports the interpolation span it used, so the basis is auditable in your report. Two boundaries on that permission are worth knowing. Interpolation is between adjacent listed temperatures only — spanning multiple rows in one straight line is not the same operation, because the rating curves steepen with temperature and a long chord cuts the corner unconservatively; interpolate in the interval your design temperature actually falls in. And there is no extrapolation in either direction: below the lowest listed temperature the lowest-temperature rating applies, and above the highest listed temperature for the class and group, the flange is simply not rated — which this calculator reports as a failure rather than a guess. The interpolation span printed on the report is there so a checker can reproduce the arithmetic in one line.

My pipe is A106 Gr B — which group is my flange?

The rating follows the flange material, not the pipe. A106 Gr B lines are normally flanged with A105 forgings — Group 1.1. If the flange is 304L or 316L (common on hygienic and clean-utility skids), that is Group 2.3, which rates noticeably lower than standard-grade stainless. The general habit this example teaches: rate the joint from the flange's marking and its MTR, never from the pipe specification, because purchasing substitutions happen at the flange level and the rating moves with them. A dual-certified F304/F304L flange rates at the straight grade's group; an L-only flange does not — the certification on the actual forging decides. And on lines assembled from mixed history — a new spool bolted to an existing nozzle — the joint rates at the lower of the two flanges, which is how a Group 1.1 system quietly inherits a Group 2.3 limit at one tie-in. When the marking is illegible, the conservative read of the available paperwork governs until the MTR is found.

Why does Class 150 stop at 1,000°F for stainless groups?

Above 1,000°F the B16.5 table shows no Class 150 rating for Groups 2.1 and 2.2 — the class is simply not rated there. The calculator returns “not rated” and fails the screen rather than extrapolating. The pattern behind the cutoff is worth seeing once: Class 150 ratings collapse toward zero much faster with temperature than the higher classes do — the 150 curve is the steepest in the book — so the standard simply stops tabulating where the rating would become impractically small. The design consequence is that hot lines leave Class 150 long before 1,000°F for margin reasons anyway; a Class 150 stainless joint near the table's edge is carrying almost no pressure capability, and the honest fix is a class step, not a hunt for a friendlier table. When the calculator returns 'not rated,' treat it as the standard telling you the class is wrong for the service, not as a data gap.

Does this cover B16.47 large-diameter flanges?

No — deliberately. B16.5 covers NPS 1/2 through 24; B16.47 Series A/B ratings are a separate standard with different tables and are not embedded here. The boundary matters in practice because NPS 26 and up is exactly where the two B16.47 series diverge from each other as well as from B16.5: Series A and Series B flanges of the same NPS and class have different bolt circles, bolt counts and thicknesses, are not interchangeable at a joint, and carry their own rating tables. A large-diameter joint therefore needs three facts confirmed — standard, series, and class — before any rating is quoted, and a mating problem between an A-series and a B-series flange is discovered at the bolt holes, which is the most expensive possible place. For those joints, read the rating from B16.47 itself for the correct series; this card will not guess it.

What about external piping loads on the flange?

The P–T rating assumes pressure only. Axial force and bending moment from the piping consume rating margin — screen them with the Kellogg equivalent-pressure check against the same rating this page returns. The order of operations that keeps this clean: rate the joint here for pressure and temperature first, then take the flexibility analysis's moment and axial force at the joint into the Kellogg equivalent-pressure screen, which converts them into an addition to the design pressure and compares the total against the same rating. A joint that passes on pressure alone but fails with the equivalent pressure added is telling you the piping loads — not the process conditions — govern that flange, and the fix is flexibility or support work upstream of any flange-class conversation. High-temperature lines deserve particular attention, because the rating is falling in exactly the operating region where thermal moments are rising.

Related calculators & tools

• Flange Equivalent Pressure Calculator (Kellogg Method) — Screen external F and M against the rating this page returns
• ASME B31.3 Allowable Working Pressure Calculator — Pipe-side allowable pressure for the same line
• ASME B31.3 Pipe Wall Thickness Calculator — Wall thickness for the pipe the flange is welded to
• Flange Bolt Tightening Sequence Calculator (Star Pattern Chart + Pass Torques) — The star-pattern bolt-up chart for assembling the joint you just rated
• PiperFLG — bolted flange analysis (Pro Plus) — The rating this page returns, derived automatically inside the flange workspace