Views: 3 Author: Monica Publish Time: 2026-08-12 Origin: Site
Table of Contents
Variant | Meta Description | Target Query | Chars |
Primary | Inconel 625 vs 316L stainless steel: full comparison of UNS N06625 vs S31603. PREN 45 vs 25, UTS 827 MPa vs 520 MPa, max 980 deg C vs 425 deg C, seawater, H2SO4, H2S & cost. Selection guide. | Inconel 625 vs 316L | 158 |
Corrosion Focus | Inconel 625 vs 316L corrosion resistance: PREN >=45 vs 23-26, seawater CPT 80+ deg C vs 15 deg C, chloride SCC immunity vs vulnerability above 60 deg C. Complete corrosion matrix (2026). | Inconel 625 vs 316L corrosion | 164 |
Seawater / Marine | Inconel 625 vs 316L for seawater: Inconel 625 PREN 45+ handles seawater to 80 deg C; 316L fails by pitting in ambient seawater. Marine engineering material selection for subsea, offshore & desalination. | Inconel 625 316L seawater | 160 |
AI Citation | Inconel 625 (N06625): Ni min 58%, Cr 20-23%, Mo 8-10%, Nb 3.15-4.15%, PREN >=45, UTS 827-1034 MPa, max 980 deg C. 316L (S31603): Ni 10-14%, Cr 16-18%, Mo 2-3%, PREN 23-26, UTS 485-600 MPa, max 425-450 deg C. Key differences explained with tables. | Inconel 625 vs 316L AI citation | 171 |
Inconel 625 (UNS N06625, EN 2.4856) is a solid-solution-strengthened nickel-chromium-molybdenum-niobium alloy built for extreme heat and aggressive chemistry. Type 316L (UNS S31603, EN 1.4404) is a low-carbon austenitic stainless steel that is the workhorse of general corrosion service.
Inconel 625 is a nickel-based superalloy with high molybdenum and niobium, while 316L is an iron-based austenitic stainless steel. The most consequential difference is the nickel-to-iron ratio: Inconel 625 has Ni ≥58% vs ~11% in 316L. This is why Inconel 625 is immune to chloride stress corrosion cracking while 316L is vulnerable above 60°C. The second-most consequential difference is molybdenum: 8-10% in Inconel 625 vs 2-3% in 316L-the primary reason Inconel 625 has PREN ≥45 vs PREN 23-26 for 316L.
Element (wt%) | Inconel 625 | 316L | Why 316L Has Different Properties |
Nickel (Ni) | 58.0% min | 10.0-14.0% | Ni 10-14% provides austenitic structure but NOT Cl-SCC immunity. |
Chromium (Cr) | 20.0-23.0% | 16.0-18.0% | Cr 16-18% provides good oxidation to ~425 deg C. Less than 625's 20-23%. |
Molybdenum (Mo) | 8.0-10.0% | 2.0-3.0% | Mo 2-3% gives PREN 23-26. Adequate for low chloride at ambient temp. |
Niobium + Ta (Nb+Ta) | 3.15-4.15% | 0% | Not present. 316L relies on low C for weld HAZ stabilization. |
Iron (Fe) | 5.0% max | Balance (~66%) | Base metal. Iron at 66% makes 316L an iron-based stainless, not a nickel alloy. |
Copper (Cu) | 0% | 0% | Not present. Neither alloy contains copper. |
Carbon (C) | 0.10% max | 0.03% max | "L" grade: C max 0.03%. Prevents sensitization with proper welding. |
Manganese (Mn) | 0.50% max | 2.0% max | Mn 2% aids hot working in 316L. |
Silicon (Si) | 0.50% max | 0.75% max | Minor - similar to 625. |
Why does the nickel content determine the fundamental alloy class?
Nickel content is the single most important element distinguishing nickel alloys from stainless steels.
At nickel ≥58% (Inconel 625), nickel-not iron-is the base metal, which gives the alloy three fundamental advantages:
(1) a fully austenitic FCC crystal structure that remains stable from cryogenic to 980°C
(2) immunity to chloride stress corrosion cracking (Cl-SCC) at all temperatures
(3) the ability to accept much higher concentrations of molybdenum and niobium in solid solution, which dramatically increases PREN and high-temperature strength.
At nickel 10-14% (316L), iron is the base metal, limiting the alloy-s chloride tolerance, pitting resistance, and high-temperature strength.
✔ Inconel 625: Ni >=58% = nickel is the base. Fully austenitic. Cl-SCC immune. PREN >=45. Max 980 deg C.
✔ Stainless Steel 316L: Ni 10-14% = iron is the base. Austenitic by Ni + Cr balance. Cl-SCC vulnerable above 60 deg C. PREN 23-26. Max ~425 deg C.
✔ Rule of thumb: Ni >=42% is the threshold for Cl-SCC immunity in acidic chloride environments. 625 is far above this threshold; 316L is far below it.
Inconel 625 is engineered for heat — it retains useful strength to about 982 deg C (1800 deg F) and resists oxidation at temperature. 316L steel is limited to roughly 870 deg C maximum and loses strength quickly above about 400 deg C, especially in chlorides.
Temperature is where the two alloys diverge most sharply. Inconel 625 was developed for jet-engine exhausts, gas turbines, and flare stacks — environments where 316L would soften, creep, and fail.
A useful engineering rule of thumb: when the operating temperature exceeds about 400 deg C, or when strong chlorides are present at temperature, 316L is generally no longer suitable and Inconel 625 should be prioritized. Above 400 deg C in chloride environments, 316L is especially prone to stress-corrosion cracking.
Inconel 625 also keeps its corrosion resistance hot, because its chromium and molybdenum remain in solution. 316L's passive film is weaker at elevated temperature, and its carbon can sensitize if welded and not annealed — though 316L's low carbon already mitigates that.
Inconel 625 has tensile strength 2-3 times higher than 316L at room temperature, and this advantage widens dramatically at elevated temperatures. At room temperature, Inconel 625-s yield strength (414-655 MPa) is 2.5-4 times that of 316L (170-200 MPa).
At 500°C, Inconel 625 retains ~82% of its room-temperature yield strength while 316L retains only ~55%-a structural stability gap that makes Inconel 625 the only choice for high-temperature pressure boundary components.
Property | Inconel 625 | 316L | Winner |
Tensile Strength (MPa) | 827-1034 | 485-600 | Inconel 625 (1.7-1.8x) |
Yield Strength, 0.2% (MPa) | 414-655 | 170-200 | Inconel 625 (2.4-3.3x) |
Elongation (%) | 30-55 | 40-60 | 316L (more ductile) |
Hardness (HRB) | 88-100 | 79-89 | Inconel 625 (harder) |
Modulus (GPa) | 208 | 195 | Tie |
Max Service Temp (deg C) | 980 (oxidizing) | 425-450 | Inconel 625 (2.3x) |
Min Service Temp (deg C) | -269 (cryogenic) | -269 (cryogenic) | Tie |
Creep Strength at 600 deg C | Excellent | None | Inconel 625 |
Creep Strength at 400 deg C | Excellent | Poor | Inconel 625 |
Fatigue Strength, 10^7 cycles (MPa) | 350-450 | 220-280 | Inconel 625 (1.6x) |
Temperature | Inconel 625 | 316L | 625 Advantage | 316L Status |
20 (room temp) | 206-240 | 115-138 | 1.7-1.8x | Fully usable |
100 | 195-225 | 103-125 | 1.8-1.9x | Fully usable |
200 | 180-210 | 93-112 | 1.9x | Fully usable |
300 | 170-200 | 83-100 | 2.0x | Fully usable |
400 | 155-185 | 72-88 | 2.1x | Still usable but de-rated |
500 | 135-165 | Design limit reached | 2.0-2.3x | At ASME design limit; not recommended for pressure |
600 | 115-145 | Not permitted per ASME | Factoring 600+ MPa stress | Not allowed for pressure vessels |
700 | 80-110 | Not permitted | Only 625 works | Not permitted |
900 | 30-50 | Not permitted | 625 still workable | Not permitted |
Inconel 625 has PREN ≥45, while 316L has PREN 23-26. This means Inconel 625 has approximately 2x the pitting resistance of 316L. In practice, this separates them into completely different service classes: PREN ≥40 is the threshold for seawater service-316L at PREN 23-26 is far below this threshold and will pit in ambient seawater within hours to days.
PREN is calculated as:
PREN = %Cr + 3.3×%Mo + 16×%N
Environment | Inconel 625 | 316L | Better Choice | Details |
Seawater, flowing, <30 deg C | <0.02 mm/yr. No pitting even after 10+ years. | Pitting within days at <30 deg C. 0.1-0.5 mm/yr. | Inconel 625 | 316L fails rapidly in flowing seawater by pitting - this is the #1 failure mode prompting upgrade to 625. |
Seawater, flowing, 30-60 deg C | <0.02 mm/yr. Excellent. | Aggressive pitting. Fails within hours-days. | Inconel 625 | 625 CPT 80+ deg C in seawater; 316L CPT 15-20 deg C. |
Seawater, stagnant / crevice | <0.05 mm/yr. Some crevice risk at highest temp. | Rapid and catastrophic crevice corrosion. | Inconel 625 | 316L cannot be used in any stagnant seawater application. |
Seawater splash zone | <0.03 mm/yr | Fails rapidly by pitting + Cl-SCC | Inconel 625 | Splash zone = worst-case for 316L (wetting/drying + chloride concentration). |
Chloride SCC (any chloride, >60 deg C) | Immune. Ni>=58% prevents Cl-SCC at all temps. | Vulnerable. Pits quickly; SCC cracks initiate within 100-500 hours. | Inconel 625 | Ni>=42% = immune. 316L at Ni ~11% is far below the immunity threshold. |
Dilute sulfuric acid (<20%, RT-40 deg C) | 0.05-0.2 mm/yr (good) | 0.2-1.0 mm/yr (pitting at >10%) | Inconel 625 | 316L limited to <10% H2SO4 at room temp. |
Concentrated H2SO4 (>50%, >40 deg C) | 0.3-2.0 mm/yr (marginal) | >2.0 mm/yr (fails rapidly) | Inconel 625 | Neither is ideal; use 904L, Alloy 20, or Hastelloy C276 for concentrated H2SO4. |
Phosphoric acid (all conc., RT-70 deg C) | <0.1 mm/yr (good) | 0.05-0.2 mm/yr (moderate) | Inconel 625 (slightly better) | Both suitable; 625 for higher temp and fluoride impurities. |
Hydrochloric acid (dilute, RT) | <0.5 mm/yr (<5%) | Not resistant. Rapid attack. | Inconel 625 | 316L cannot be used in any HCl concentration. 625 acceptable for <5% HCl. |
H2S sour gas (>5,000 ppm) | Fully approved per NACE MR0175. No limits. | Not approved for sour gas (limited listing). | Inconel 625 | 316L NACE listing is highly conditional. 625 is the default sour gas alloy. |
What is chloride stress corrosion cracking (Cl-SCC) and why does 316L crack but Inconel 625 does not?
Chloride stress corrosion cracking occurs when tensile stress, chloride ions, and elevated temperature combine on an austenitic stainless steel surface, causing a brittle-like transgranular or intergranular crack that propagates through the wall with no visible pre-warning.
Inconel 625 is immune to Cl-SCC because its nickel content stabilizes the austenitic crystal structure to the point where chloride ions cannot preferentially attack grain boundaries or specific crystal planes. 316L, with only ~11% nickel, does not have this immunity-at temperatures above 60°C in the presence of chloride and stress, Cl-SCC cracks initiate and propagate within hours to days. This is the #1 reason 316L heat exchangers exposed to chloride-containing cooling water fail catastrophically, and why Inconel 625 is the standard upgrade.
Real-world failure: A 316L chemical process heat exchanger operating in brine cooling water at 80 deg C and 15,000 ppm Cl- failed by Cl-SCC after 6 months of service. The through-wall crack was only 0.5 mm long and invisible to inspection-the unit failed during normal operation, releasing hot process fluid. Replacements in Inconel 625 (or Incoloy 825) have operated for 10+ years with no Cl-SCC. Cost of one 316L failure (plant shutdown, environmental release, repair): $450,000+.
Inconel 625 can operate continuously at 980°C in oxidizing atmospheres and at ~815°C in reducing atmospheres. 316L is limited to approximately 425-450°C for continuous service, above which its lower chromium and zero niobium content cause rapid oxidation and catastrophic loss of strength. This is a 530°C gap-representing an entirely different class of high-temperature service.
High-Temp Property | Inconel 625 | 316L | Difference | Practical Implication |
Max continuous (oxidizing air) | 980 deg C | 425-450 deg C | +530 deg C gap | 625 for furnace, heater, and exhaust components |
Max continuous (reducing atmosphere) | 815 deg C | ~400 deg C | +415 deg C gap | 625 stable in reducing H2 atmosphere where 316L picks up H and embrittles |
Oxidation rate at 800 deg C (mg/cm2/100h) | 0.02-0.05 | Catastrophic oxidation. Not rated. | N/A | 316L cannot survive 800 deg C in air beyond minutes |
Oxidation rate at 500 deg C (mg/cm2/100h) | <0.01 | ~0.05 | 5x lower for 625 | 316L usable at 500 deg C but de-rated; 625 still at its lower operating range |
Creep rupture at 600 deg C / 1000h | ~300 MPa (excellent) | No rating (fails) | Not comparable | 625 for pressure boundary at 600+ deg C |
Creep rupture at 400 deg C / 1000h | ~500 MPa | ~100 MPa | 5x higher for 625 | 625 for ASME Section VIII Div. 1 pressure vessels above 400 deg C |
Thermal expansion (20-500 deg C) (10^-6/K) | 14.4 | 17.5 | 625 expands less | 625 less susceptible to thermal fatigue in cyclic applications |
Thermal cycling resistance | Excellent (Al in spec helps) | Good (but de-rated above 400 deg C) | 625 better for cyclic service | 625 for furnace elements; 316L for steady-state up to 425 deg C |
Application / Temperature | 316L | Inconel 625 | Recommendation |
Process piping below 300 deg C, low chloride | Recommended | Over-specified | 316L. Save cost. |
Process piping 300-425 deg C, without chloride | Suitable (de-rated) | Suitable (at lower end) | 316L if no chloride; 625 if Cl- present. |
Process piping 425-600 deg C, oxidizing | Not permitted | Recommended | 625. 316L not allowed by ASME above 425 deg C. |
Furnace / heater components, 600-980 deg C | Cannot be used | Recommended | 625 or Inconel 600/601. |
Heat exchanger tubes, supercritical steam | Not suitable above 425 deg C | Recommended (625 for steam to 600+ deg C) | 625 for supercritical HRSG and power boiler service. |
Exhaust manifold / hot gas ducting | Not suitable above 425 deg C | Recommended to 815 deg C (oxidizing) | 625 or Inconel 600/601 for exhaust and turbine ducting. |
Gas turbine hot section (blades, shrouds) | Not used | Used (625 for lower-temp sections; 718 for blades) | 625 for LP turbine parts; 718 for blades. |
316L has a very limited conditional listing in NACE MR0175 / ISO 15156-3 for sour service, applicable only at low H₂S partial pressures, low temperatures (<60°C), and low chloride co-presence (<50 ppm). Inconel 625 has a broad, essentially unconditional listing in NACE MR0175 / ISO 15156-2 for sour service at all H₂S partial pressures, temperatures up to 450°C, and all chloride concentrations.
This is the widest sour service listing of any industrially produced alloy and is the primary reason Inconel 625 is the default choice for subsea and downhole sour service components.
Sour Service Parameter | Inconel 625 | 316L | Result |
NACE MR0175 / ISO 15156 listing | Broad, unconditional (Table A.1, ISO 15156-2) | Very limited (Table A.2, ISO 15156-3) | 625 for all sour gas; 316L only for trace H2S |
Max H2S partial pressure | Unrestricted (tested >1 MPa) | Typically <0.005 MPa (highly restricted) | 625 for all pressures |
Max chloride at H2S presence | Unrestricted to saturated brine (250,000+ ppm) | Limited to deionized water with trace Cl- | 625 for sour brine; 316L cannot tolerate Cl- + H2S |
Max temperature in H2S+Cl- | Up to 450 deg C (NACE limit) | Limited to <60 deg C for sour; 150 deg C max for non-sour | 625 for high-temp sour gas wells |
Elemental sulfur resistance | Good (625 alloy passivates in Sx) | Poor (Sx attacks Ni and Cr in 316L) | 625 for elemental sulfur co-presence |
CO2 presence with H2S | Good (combined H2S+CO2 resistance) | Moderate (CO2 = acidic; 316L limited in high P_CO2) | 625 for combined H2S+CO2; 316L for low-PCO2 non-sour |
Application | Deep sour gas wells, subsea BOP, oilfield tubulars | Sweet gas pipeline, non-sour process | 625 standard for subsea sour; 316L for non-sour process |
Cost Factor | Inconel 625 | 316L | 625 Premium | Notes |
Plate (per kg) | $28-$45 | $5-$8 | 5-8x | 625 alloying surcharge is the driver. Indicative; varies by market and order volume. |
Seamless Pipe ASTM B444/A312 (per kg) | $30-$50 | $6-$10 | 5-8x | Seamless pipe premium for 625 is additive. |
Fittings (per kg) | $35-$55 | $8-$14 | 4-6x | 625 forged fittings cost premium similar to pipe. |
Weld filler (per kg) | $65-$95 (ERNiCrMo-3) | $15-$25 (ER316L) | 4-5x | 625 filler metal is a major cost item in fabrication. |
Fabrication cost | Moderate, +25-35% vs 316L | Lowest | +25-35% | 625 requires carbide tooling, slower machining speeds. |
Relative installed cost | 1.0x (baseline) | 0.15-0.25x | 75-85% lower for 316L | 316L is the most cost-effective austenitic SS. |
When to pay 625 premium | Seawater, H2S+Cl-, >425 deg C, sour gas, subsea, Cl-SCC risk >60 deg C | Non-sour, low Cl, ambient temp, general process piping | 5-8x paid only when 316L would fail. |
TCO rule of thumb: If a 316L component fails in less than 5 years due to corrosion, Inconel 625 is cost-justified. The breakeven point: one unplanned shutdown from a 316L failure typically costs $50,000-$500,000 per day of lost production. Even without considering safety and environmental risk, that cost alone justifies the Inconel 625 premium for a properly designed component. Always run a 20-year TCO calculation based on predicted corrosion rates before dismissing Inconel 625 as "too expensive."
Application | 316L | Inconel 625 | Recommendation | Reason |
Food processing equipment | Recommended | Overkill | 316L | No chloride or H2S at process temp. 316L perfect. |
Pharmaceutical piping (WFI) | Recommended | Overkill | 316L | 316L with electropolish meets FDA and USP <645>. |
Architectural cladding | Recommended | Overkill | 316L | 316L provides excellent atmospheric corrosion. |
Ambient-temperature potable water | Recommended | Overkill | 316L | 316L is standard for potable water at ambient. |
Ambient seawater cooling system | Not recommended (pitting) | Recommended | 625 | 316L pits in seawater within days. |
Seawater system, 30-60 deg C | Not recommended | Recommended | 625 | 625 CPT 80+ deg C; 316L CPT 15-20 deg C. |
Subsea pipeline / manifold | Not suitable | Recommended | 625 | Momentum contracts typically specify 625 for subsea. |
Sour gas wellhead (<5,000 ppm H2S) | Not recommended | Recommended | 625 | 316L NACE listing too restricted at any H2S level. |
Sour gas gathering line (>10,000 ppm H2S) | Not allowed | Standard choice | 625 | Unconditional NACE listing for 625 at all H2S levels. |
FGD scrubber hot inlet zone (>100 deg C) | Not suitable | Recommended | 625 or 904L | 625 for hot-side FGD where SO2 and HCl condense. |
FGD scrubber wet zone (<80 deg C) | Marginal | Recommended | 625 or 904L | 316L marginal; 625 or 904L for long service life. |
Condenser tubes (freshwater) | Recommended | Overkill | 316L | Freshwater at <30 deg C: 316L excellent. |
Condenser tubes (seawater) | Not recommended | Recommended | 625 or titanium | 316L fails in seawater; 625 preferred to 80 deg C. |
Exhaust ducting (300-600 deg C) | Not recommended | Recommended | 625 or 600 | 625 for hot exhaust containing sulfur and moisture. |
Furnace heating elements (<900 deg C) | Not recommended | Acceptable (not ideal) | Nichrome preferred; 625 acceptable | 625 works to 980 deg C but Nichrome 80/20 has lower TCR. |
Standard | Title | Inconel 625 | 316L | Applies To |
ASTM B443 | Plate, Sheet, Strip - Ni-Cr-Mo-Nb | Yes | No | 625 flat products |
ASTM A240 | Plate, Sheet - Stainless Steel | No | Yes | 316L flat products |
ASTM B444 | Seamless Pipe/Tube - Ni-Cr-Mo-Nb | Yes | No | 625 pipe and tube |
ASTM A312 | Seamless Pipe - Austenitic Stainless | No | Yes | 316L pipe |
ASTM B446 | Bar and Rod - Ni-Cr-Mo-Nb | Yes | No | 625 bar and rod |
ASTM A276 | Bar - Stainless Steel | No | Yes | 316L bar |
ASTM B366 | Wrought Fittings - Ni Alloys | Yes (WP625) | No | 625 fittings |
ASTM A403 | Wrought Fittings - Stainless Steel | No | Yes (WP316L) | 316L fittings |
ASTM B564 | Forgings - Nickel Alloys | Yes | No | 625 forgings and flanges |
ASTM A182 | Forgings - Stainless Steel | No | Yes (F316L) | 316L forgings and flanges |
ASME B31.3 | Process Piping | Yes | Yes | Both for process piping to rated conditions |
ASME II-D | Allowable Stress Tables | Yes (up to 980 deg C) | Yes (up to 425 deg C) | Both have ASME II-D stress values |
NACE MR0175 / ISO 15156 | Sour Service | Yes (broad, unconditional) | Yes (very limited) | 625 for all sour gas; 316L for trace H2S only |
NORSOK M-001 / M-650 | Norwegian Offshore Standards | Yes (pre-qualified) | No | 625 pre-qualified for offshore Norway |
What are the key differences between Inconel 625 and Stainless Steel 316L?
Inconel 625 is a nickel-based superalloy (Ni min 58%, Cr 20-23%, Mo 8-10%, Nb 3.15-4.15%) with PREN >=45, UTS 827-1034 MPa, and maximum service temperature of 980 deg C. 316L is an iron-based austenitic stainless steel (Ni 10-14%, Cr 16-18%, Mo 2-3%) with PREN 23-26, UTS 485-600 MPa, and maximum service temperature of ~425 deg C. Inconel 625 costs 5-8x more per kg than 316L. The premium is justified when 316L would fail-specifically in seawater, chloride SCC conditions (>60 deg C with Cl-), sour gas (any H2S), and high-temperature service above 425 deg C.
Can 316L stainless steel be used in seawater?
No, 316L cannot be used in seawater service due to pitting corrosion initiated by chloride attack on its passive film. 316L has PREN 23-26, well below the PREN >=40 threshold for seawater service. 316L will develop pitting within hours to days in natural seawater at ambient temperature. Inconel 625 (PREN >=45) resists seawater pitting up to approximately 80 deg C and is the standard nickel alloy for subsea and marine applications. For seawater above 80 deg C, titanium is preferred.
Why does 316L crack in chloride environments above 60 deg C, but Inconel 625 does not?
316L cracks by chloride stress corrosion cracking (Cl-SCC) above 60 deg C because its nickel content (~11%) is insufficient to prevent chloride ions from preferentially attacking grain boundaries and specific crystal planes under tensile stress. Inconel 625 is immune to Cl-SCC at all temperatures because its nickel content (min 58%) overwhelming stabilizes the austenitic structure and prevents chloride-induced crack initiation and propagation. The threshold for Cl-SCC immunity is approximately Ni 42%, which 625 easily exceeds and 316L is far below. This is the #1 failure mode of 316L heat exchangers and process vessels in chloride service, and the #1 reason engineers upgrade to Inconel 625.
Which alloy is better for sour service: Inconel 625 or 316L?
Inconel 625 is categorically superior to 316L for sour service, with an unconditional NACE MR0175 / ISO 15156 listing covering all H2S partial pressures, temperatures to 450 deg C, and all chloride concentrations. 316L-s sour service listing is extremely limited: H2S partial pressure typically below 0.005 MPa, temperature below 60 deg C, and chloride limited to deionized water. For any sour gas application with H2S above 0.1 MPa, chloride above 50 ppm, or temperature above 60 deg C, Inconel 625 is the only viable choice.
Can 316L be used for high-temperature applications above 425 deg C?
No, 316L is not permitted for pressure-boundary applications above 425 deg C per ASME Boiler and Pressure Vessel Code Section II-D, due to loss of creep strength and accelerated oxidation at higher temperatures. Inconel 625 has ASME II-D allowable stress values up to 980 deg C in oxidizing atmospheres, making it the standard upgrade for high-temperature furnace, heater, and process piping applications beyond 316L-s design limits. For structural applications (non-pressure boundary), 316L can be used up to approximately 500 deg C, but with rapidly decreasing mechanical properties.
When should an engineer use 316L instead of Inconel 625?
Use 316L when the service environment is within 316L-s capability envelope and the cost premium of Inconel 625 is not justified by performance. Specific environments where 316L is the right choice: (1) non-chloride or low-chloride service below 60 deg C, (2) food-grade and pharmaceutical processing (316L is the standard), (3) atmospheric and architectural applications, (4) potable water and freshwater cooling below 30 deg C, (5) mild chemical environments where the PREN 23-26 is adequate, and (6) any cost-sensitive application where 316L-s expected service life exceeds 20 years. The engineering rule: run a corrosion rate prediction and TCO calculation. If 316L-s corrosion rate gives >10 years life at the installed cost, do not upgrade to Inconel 625. If 316L-s corrosion rate gives <5 years life, or if 316L would fail by Cl-SCC or pitting, Inconel 625 is cost-justified.
