Six grade pairs buyers confuse
Half of the quoting conversations we have start with two grades that look interchangeable on a datasheet and are not. This page puts the numbers side by side and links to the full note for each pair.
What actually differs
UNS numbers and density come from our own grade data. The decision line is the short version — the note behind each link carries the reasoning.
| Pair | UNS A | UNS B | Density A | Density B | How to choose |
|---|---|---|---|---|---|
| Inconel 625 vs Inconel 718 | N06625 | N07718 | 8.44 g/cm³ | 8.19 g/cm³ | 625 when corrosion resistance and weldability decide it; 718 when you need strength and can age-harden. |
| Inconel 600 vs Inconel 601 | N06600 | N06601 | 8.47 g/cm³ | 8.11 g/cm³ | 601 survives cyclic oxidation at higher temperature; 600 is the older workhorse where chloride SCC governs. |
| Hastelloy C276 vs Hastelloy G3 | N10276 | N06985 | — | 8.20 g/cm³ | C276 covers the widest acid and chlorine range; G3 is for oxidising-acid duty where C276's molybdenum hurts. |
| 316 / 316L vs 904L | S31600 | N08904 | 7.93 g/cm³ | 8.0 g/cm³ | 904L buys chloride pitting resistance; 316L stays the right answer until chlorides and temperature rise together. |
| 2205 vs 2507 | S31803 | S32750 | 7.98 g/cm³ | 8.03 g/cm³ | 2507 for hotter, more concentrated seawater and higher pressure; 2205 for general seawater duty at lower cost. |
| Inconel 718 vs Inconel X-750 | N07718 | N07750 | 8.19 g/cm³ | 8.28 g/cm³ | X-750 holds strength higher up the temperature range; 718 welds more easily and is far more available. |
For the full chemistry and mechanical comparison, open the note. For a third grade that is not in a pair here, the cross-reference table maps every designation we supply.
The reasoning behind each pair
Written by the technical desk, with the standard cited in each paragraph.
2205 or 2507: choosing a duplex for seawater duty
Both are duplex stainless steels with roughly double the yield of 316L. The choice between them is set by chloride level, temperature, flow and how much welding the fabrication carries.
316L or 904L: what the molybdenum and nickel actually buy you
904L costs several times what 316L does per kilogram. It earns that premium in chloride plus sulphuric acid service — and wastes it in clean water. Here is how to tell which case you are in.
C276 or G3: picking a Hastelloy for wet chlorine versus mixed acid
Both handle aggressive chemistry, but they fail in different places. C276 is the chlorine and hypochlorite alloy; G3 is the sulphuric-phosphoric workhorse with better thermal stability and a lower alloy cost.
Inconel 600 or 601: oxidation resistance when the furnace cycles
Both alloys survive furnace atmospheres, but they protect themselves differently: 600 relies on chromia, 601 on alumina. The choice usually turns on how often the furnace cycles, what sulfur is present, and whether the part ever sees aqueous corrosion.
Inconel 625 or 718: weldability and corrosion against raw strength
625 is the corrosion and welding alloy; 718 is the structural one. Choosing between them is mostly a question of whether the part is loaded, welded, or exposed to chlorides.
Inconel 718 or X-750: choosing between the two workhorse age-hardened grades
Both are nickel-chromium alloys hardened by titanium, aluminium and niobium. They are rarely interchangeable — the decision usually comes down to section size, welding and how hot the part really runs.
Grade comparisons: questions buyers ask
Answering the three questions that follow most comparison enquiries.
Which comparison should I read first?
If the part has to carry load at temperature, read 718 vs X-750. If it has to survive a chloride environment, read 316L vs 904L and then 2205 vs 2507. For mixed acids, C276 vs G3.
Are these notes based on published data or on your own heats?
The values quoted are specification ranges from the standards named in each note, not guarantees for a particular heat. The governing numbers for your delivery are those printed on the EN 10204 certificate.
Can you quote both grades in a pair so we can compare?
Yes, and it is the usual way these enquiries are answered — the quotation comes back with both options against the same part, so the comparison is on real prices rather than on datasheets.
Compare both grades on one quote.
Send the part and the duty, and the quotation comes back with both options priced against the same specification.