ISO 21857:2021

Overview

ISO 21857:2021 - Petroleum, petrochemical and natural gas industries - Prevention of corrosion on pipeline systems influenced by stray currents - provides guidance for evaluating and minimizing external corrosion on buried or immersed pipeline systems caused by stray currents and electrical interference (both DC and AC). The standard covers identification, measurement, assessment and mitigation of stray-current–induced corrosion on external surfaces of pipelines and similar buried or immersed metallic structures. It is applicable beyond oil and gas to other buried metal structures (cables, tanks, sheet piling, reinforced concrete, earthing systems).

Key technical topics and requirements

• Identification and measurement of stray current interference: principles for measuring potentials, currents (including use of current probes), duration and data acquisition considerations, and avoiding AC measurement errors.
• Assessment methods: use of potential analysis and direct corrosion-rate measurement (e.g., electrical resistance probes) where stray currents distort cathodic-protection potentials.
• Acceptance criteria for DC interference: guidance for establishing criteria and assessing corrosion risk under time‑constant and time‑variant interference conditions (no numeric thresholds given in the standard summary).
• Mitigation and reduction strategies:
  • Modifying sources of interference (traction systems, industrial DC systems, cathodic protection units, HVDC and telluric effects).
  • Design and modification of the interfered structure (coatings, electrical isolation, maximizing separation, installation of mitigation devices, modifying electrical continuity).
• Design guidance for cathodic protection systems that might produce stray currents and selection of appropriate protection/mitigation measures.
• Inspection and maintenance routines and documentation requirements.
• Informative annexes covering AC interference, HVDC, geomagnetic/tidal effects, photovoltaic interference, modelling, and measurement techniques.

Practical applications and users

ISO 21857:2021 is intended for professionals responsible for corrosion control and pipeline integrity, including:

• Pipeline operators and asset owners in petroleum, petrochemical and natural gas industries
• Corrosion and cathodic protection engineers
• Pipeline designers and electrical/traction system engineers
• Maintenance and inspection teams, consultants and regulators

Typical uses:

• Evaluating stray-current risk during planning, design and operation of buried pipelines
• Designing cathodic protection and mitigation measures to prevent stray-current corrosion
• Investigating interference incidents from rail traction, HVDC, industrial DC systems or natural geomagnetic events
• Developing inspection, monitoring and maintenance programs for affected assets

Related standards

• ISO 18086 (AC effects on buried/immersed pipelines)
• ISO 15589-1 / ISO 15589-2 (cathodic protection for pipelines)
• EN 50162 (railway-related structures)
• EN 50443, IEC 61140, IEC 60364 series, IEC/TS 61201, IEC/TR 60479-5 (electromagnetic/electrical safety and interference guidance)

Keywords: ISO 21857:2021, stray currents, pipeline corrosion, cathodic protection, AC interference, DC interference, corrosion mitigation, buried pipelines, electrical interference.