ISO 3171:1988

Overview

ISO 3171:1988 - Petroleum liquids - Automatic pipeline sampling provides internationally accepted guidance for obtaining representative automatic samples of crude oil and liquid petroleum products transported by pipeline. The standard (second edition, 1988) covers selection, specification, testing, operation, maintenance and monitoring of automatic sampling systems used to determine bulk composition, water and sediment content, density and related quality attributes. It excludes liquefied petroleum gases (LPG) and liquefied natural gas (LNG).

Keywords: ISO 3171, automatic pipeline sampling, petroleum liquids, crude oil sampling, pipeline sampling standard

Key topics and technical requirements

• Scope and purpose: Procedures and minimum practices for automatic sampling to obtain representative pipeline samples for laboratory analysis and quantity/quality adjustments.
• Definitions & principles: Concepts such as grab, flow-proportional and time-proportional sampling, isokinetic sampling, sampler performance factor (PF), profile testing and sample integrity.
• Sampler types and design: Guidance on intermittent (grab) samplers and continuous samplers, sampling probe design, multipoint probes and installation considerations.
• Stream conditioning & mixing: Requirements for adequate stream conditioning (static or powered mixers) upstream of the sampling point to ensure homogeneity before sampling.
• Profile testing: Multipoint sampling across a pipe diameter to verify concentration profiles (water-in-oil dispersion) and acceptability of sampling locations.
• Control & flow measurement: Specification of controllers and flow measurement requirements to ensure proportional sampling and correct sampling frequency.
• Sample receivers & handling: Design and handling practices to preserve sample integrity during transfer, division and transport to laboratory.
• Operation, maintenance & proving: Procedures for routine operation, maintenance log/reporting, proving/validation tests and estimating overall sampling system uncertainty (clauses and annexes provide testing and calculation guidance).
• Safety: Safety precautions applicable to petroleum sampling systems and equipment.

Practical applications and users

ISO 3171 is used by:

• Oil producers, refinery and terminal operators for custody transfer and quality control
• Pipeline operators and metering teams to specify and validate automatic sampling systems
• Procurement and engineering teams selecting samplers, probes and mixers
• Laboratories and QA/QC personnel interpreting sample representativity and uncertainty
• Regulatory bodies and third-party inspectors assessing sampling compliance

Practical benefits include improved accuracy of water and sediment measurements, reduced sampling bias during transfers, and documented procedures for sampler proving and uncertainty estimation.

Related standards

• ISO 3170 - Petroleum products - Manual sampling (complements automatic sampling)
• ISO 3165 - Sampling of chemical products for industrial use - Safety in sampling

For implementers, consult the full ISO 3171:1988 text and its annexes for detailed test methods, tables and example profile-test data.