Bottom line first: No. Propane and propylene are measurable components under ASTM D3612, but they play no role in the fault-interpretation criteria of IEC 60599, IEEE C57.104, DL/T 1498 or DL/T 722. Writing “C3 is a required standard component” into a purchase specification is one of the most widespread misreadings in the industry.
More to the point: IEC 60599:2022 devotes a dedicated clause — §5.8, “C3 hydrocarbons” — to the subject. The content of that clause is that C3 has been excluded from the interpretation method.
1. What the standards actually say
IEC 60599:2022 Ed. 4, §5.8 (verbatim)
“The interpretation method of gas analysis indicated in 5.1 to 5.7 takes into account only C1 and C2 hydrocarbons. … Because the C3 hydrocarbons are very soluble in oil, … they are difficult to extract from the oil and the result of the analysis can greatly depend on the extraction method used. Moreover, experience has shown that, in most cases, a satisfactory diagnosis can be made without taking into account these hydrocarbons and for the sake of simplification, they have been omitted from the interpretation method indicated in 5.1 to 5.7.“
In one sentence: C3 is highly soluble, difficult to extract, and its measured value depends heavily on the degassing method — so, for simplicity, the interpretation method leaves it out.
Where C3 stands in each standard
| Standard | Status of C3 |
|---|---|
| ASTM D3612 (GC method) | Listed as a measurable component (the 11-component list includes propane C₃H₈ and propylene C₃H₆) — but this is a measurement method, not a criterion |
| IEC 60599:2022 | Gas table covers 9 gases with no C3; §5.8 explicitly excludes C3 from interpretation |
| IEEE C57.104-2019 | Components limited to H₂ / CH₄ / C₂H₆ / C₂H₄ / C₂H₂ / CO / CO₂ — no C3 limit |
| GB/T 17623 | Primary list is 9 gases; a note states propane and propylene “may also be measured by reference to this method” (not primary) |
| DL/T 1498.2 / DL/T 722 | No C3 |
Put simply: C3 appears in the standards that say how to measure, not in the standards that say how to judge.
2. Why this misreading is bad for procurement
Writing “C3 is a required standard component” into a specification has three consequences:
- It tilts the tender the wrong way. Mature equipment that does not measure C3 — the large majority of online DGA worldwide — gets ruled “non-compliant”, excluding valid solutions.
- It raises the risk of misdiagnosis. C3 is highly soluble and hard to extract, so different degassing methods produce very different C3 values — which is precisely why IEC excluded it. A headspace unit and a vacuum unit testing the same oil can read C3 several times apart.
- It distracts from the real problems. What actually drives diagnostic quality are the criteria gases — H₂, C₂H₂ and C₂H₄ — not C3.
3. So when is C3 useful?
It is useful — placed correctly, as an auxiliary or differentiating signal, never as a threshold.
- The full ASTM D3612 GC workflow can measure C3, and laboratory-grade analysis has long used it as supporting information.
- A few manufacturers have published academic observations on how C3 ratios shift with temperature, but this constitutes no standard clause and cannot be marketed as a compliance criterion.
- Among online commercial analyzers, few output C₃H₆/C₃H₈ as a distinct channel. One example is Hitachi’s CoreSense M10, which uses a full-spectrum FTIR platform (per the manufacturer’s published specifications).
Our recommendation: if a customer genuinely wants to see C3, the correct wording is —
“Within the ASTM D3612 GC measurement framework, an optional C₃H₆/C₃H₈ channel can be added as an auxiliary reference for overheating diagnosis.”
That is not the same as “C3 is a required standard component.” A one-word difference with a very large difference in compliance risk.
4. Three plain truths for buyers
- When specifying DGA, first ask “are the criteria gases measured?” (H₂, CH₄, C₂H₆, C₂H₄, C₂H₂, CO, CO₂), then discuss extensions.
- Require suppliers to cite the clause number and text of the standard they claim to meet — not a general statement of “complies with the standard”.
- If a tender lists “C3 / propane / propylene” as a mandatory threshold, it was most likely copied from the wrong source.
Standards clauses cited from the full text of IEC 60599:2022 Ed. 4, the official scope of ASTM D3612, IEEE C57.104-2019, GB/T 17623, DL/T 1498.2-2016 and DL/T 722-2014.
William Xiong — Shenzhen Feso Automation Technology Co., Ltd (PAS DGA) · Online monitoring of dissolved gases in transformer oil · Hydrogen sensing
inquiry@pasdga.com · https://pasdga.com
If you would like to align a DGA specification with the correct interpretation clauses, or discuss the PAS DGA-500 hydrogen channel, we welcome the conversation.