ISO 10715 Natural Gas Sampling: International Practice for Pipeline and Custody Sampling

Why ISO 10715 Exists

ISO 10715:1997 ("Natural gas — Sampling guidelines") is the international counterpart to API MPMS Chapter 14.1 in the US and GPA 2166 in the gas processing industry. It exists because international gas trade — pipeline interconnects, LNG export, cross-border transactions — requires a single document that all parties can reference.

The three standards overlap heavily, but ISO 10715 is the one written from a regulator's perspective and the one most often cited in international commercial contracts.

What It Covers

1. Probe design requirements for representative sampling

2. Sample line material and slope

3. Sample cylinder preparation and conditioning

4. Sample handling under hydrocarbon dew-point conditions

5. Documentation for custody transfer audit trails

Probe Requirements per ISO 10715

ISO 10715 prescribes:

• Probe insertion depth ≥ 1/3 of pipe ID, with the inlet in the central 30%
• Bevelled, downstream-facing inlet to minimize liquid carryover
• Material: 316L SS minimum; upgrade for sour service per NACE
• Temperature: probe and sample line maintained ≥ 5 °C above the calculated hydrocarbon dew point
• Length: short enough to satisfy wake-frequency criteria

These requirements parallel API 14.1 closely. The major practical difference is that ISO 10715 is more explicit about dew-point control.

The Dew-Point Trap

The most common failure mode of a custody transfer probe is inlet retrograde condensation. Pipeline natural gas typically operates within a few degrees of its hydrocarbon dew point. Any pressure drop across the probe inlet — Bernoulli effects, restrictive plumbing — locally cools the gas and condenses C5+ heavies out of the vapor phase. The composition that reaches the analyzer is now lighter than the bulk gas, the BTU is biased low, and the contract is mis-billed.

ISO 10715 addresses this with three explicit rules:

1. Heat-trace the probe and sample line above the dew-point margin

2. Maintain pressure as close to pipeline pressure as practical

3. Use a membrane separator when liquid carryover cannot be avoided

Comparison with API 14.1 and GPA 2166

For practical work, an operator who satisfies API 14.1 will satisfy ISO 10715 with one extra check: documented heat trace to maintain the 5 °C margin above dew point.

Adjacent Reading

• Custody Transfer Sampling per API 14.1
• Oil & Gas Pipeline Sampling Best Practices
• Wake Frequency Analysis
• LNG Terminals Application
• Industrial Sampling Pillar