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ISO 29945:2016 — Refrigerated Non-Petroleum Based Liquefied Gaseous Fuels — DME — Manual Sampling Method
Standard method for manual sampling of refrigerated DME on board vessels | Closed-loop vapor return | Custody transfer quality
1. Scope of ISO 29945:2016
ISO 29945:2016 specifies the method for manual sampling of refrigerated non-petroleum based liquefied gaseous fuels — specifically Dimethylether (DME) — on board vessels. DME is a clean-burning alternative fuel with physical properties similar to liquefied petroleum gas (LPG) but with distinct handling challenges. Its boiling point of −24.9 °C, solvent properties, and water miscibility require specialized sampling procedures that differ significantly from conventional LPG sampling per ISO 1973.
Why DME Sampling Matters: DME is increasingly used as a clean fuel for power generation, domestic heating, and as an aerosol propellant. Accurate sampling is essential for custody transfer, quality verification, and compliance with purchase specifications. A non-representative sample can lead to disputes valued at hundreds of thousands of dollars per cargo.
2. Equipment and Procedure Requirements
The standard mandates the use of stainless steel sample cylinders designed to handle DME’s vapor pressure and material compatibility requirements. DME acts as a solvent on many elastomers, so seals must be Viton or EPDM rather than standard NBR. The sampling apparatus must be pre-cooled to prevent flash vaporization, and a closed-loop vapor-return method is strictly required to avoid atmospheric venting.
| Component | Requirement | Common Non-Conformity |
|---|---|---|
| Sample cylinder | Stainless steel, rated ≥ 2× working pressure | Use of carbon steel (corrosion risk) |
| Seal materials | Viton or EPDM | NBR O-rings (swelling and failure) |
| Filling ratio | 80 % liquid fill maximum | Overfilling (hydraulic lock risk) |
| Purge sequence | Minimum 3 purge cycles | Incomplete purging (water contamination) |
| Vapor return | Closed-loop required | Open venting (safety hazard) |
Safety Warning: DME has a wide flammability range (3.4-27 % by volume in air) and a low autoignition temperature (350 °C). Static electricity buildup during sampling must be prevented through proper bonding and grounding. Never sample during electrical storms.
3. Quality Assurance and Sample Handling
Sample integrity is maintained through strict chain-of-custody documentation. Immediately after collection, samples must be stored in a cool, shaded area at temperatures below 10 °C. Analysis for water content, purity, sulfur content, and evaporation residue should be initiated within 24 hours. The standard emphasizes that DME’s hygroscopic nature means water contamination can occur rapidly if sample cylinders are not properly dried before use.
4. Frequently Asked Questions
Q1: How does DME sampling differ from LPG sampling?
A: DME requires pre-cooled apparatus, EPDM/Viton seals, and strict drying procedures due to its −24.9 °C boiling point, solvent properties, and water miscibility.
A: DME requires pre-cooled apparatus, EPDM/Viton seals, and strict drying procedures due to its −24.9 °C boiling point, solvent properties, and water miscibility.
Q2: What is the recommended filling ratio?
A: Maximum 80 % liquid fill at the reference temperature to allow for thermal expansion without hydraulic lock.
A: Maximum 80 % liquid fill at the reference temperature to allow for thermal expansion without hydraulic lock.
Q3: Can automated sampling systems replace manual sampling?
A: ISO 29945 only covers manual sampling. For automated systems, refer to ISO 3171 or relevant API standards.
A: ISO 29945 only covers manual sampling. For automated systems, refer to ISO 3171 or relevant API standards.
Q4: How often should sample cylinders be inspected?
A: Cylinders must be hydrostatically tested every 5 years and visually inspected before each use for dents, corrosion, or damaged threads.
A: Cylinders must be hydrostatically tested every 5 years and visually inspected before each use for dents, corrosion, or damaged threads.
