ISO 28521:2009

Overview

ISO 28521:2009 - Ships and marine technology - Hydraulic oil systems - Guidance for grades of cleanliness and flushing - provides practical guidance for cleaning, flushing and verifying the internal cleanliness of hydraulic oil pipe systems on ships and marine installations. The standard explains methods and equipment to remove installation dirt, how to check cleanliness, and how to plan flushing so hydraulic systems operate trouble‑free. It clarifies the difference between a “washing-through” and a “flushing” process based on the Reynolds number (around the 3 000 threshold) to indicate laminar versus turbulent flow for effective cleaning.

Key topics and requirements

• Scope and intent: Specifies pipe‑cleaning levels and practical execution for pipes and associated components; supplements - not replaces - manufacturer instructions.
• Pre‑cleaning assumptions: Presumes pipe sections have been partly cleaned by pickling and mechanical means; supplier components (dynamic and static) should be delivered clean.
• Cleaning methods: Chemical (alkaline/pickling), mechanical blow‑through, pull‑through with lint‑free cloths, and special pump/accumulator units for inducing turbulent flow in small bore lines.
• Hydraulic flushing planning: Guidance on coupling, grouping, avoiding dead legs, bypassing sensitive components, removing built‑in filters before flushing, and changing flow direction during flushing.
• Filters and pump units: Use dedicated flushing filters (do not use permanent system filters) sized for adequate contamination capacity and flow. Portable pump stations and pulsation or gas/oil units are recommended options.
• Verification and testing: Blow/pull‑through, leakage tests (pressure, shock), filling procedures, shock/pressure cycling, sampling guidance, and particle‑counting methods to confirm cleanliness levels.
• Handling and storage: Surface treatment, blanking off, and storage recommendations to maintain cleanliness until installation.

Practical applications

• Ensures reliable, long‑term operation of hydraulic systems by preventing contamination‑related failures (valve sticking, pump wear, filter blockage).
• Used during shipbuilding, retrofits, maintenance, commissioning and shore‑based testing of hydraulic piping and equipment.
• Helps define flushing procedures, select flushing oils and filters, size temporary flushing equipment, and document acceptance test results.

Who should use this standard

• Shipyards and marine contractors conducting hydraulic pipe installation and commissioning.
• System designers and integrators planning flushable hydraulic circuits.
• Class surveyors, maintenance engineers, and equipment suppliers responsible for ensuring and documenting cleanliness before system start‑up.

Related standards

• ISO 4406 (contamination coding by particle count)
• ISO 28523 (sampling for cleanliness and particle contamination)

Keywords: ISO 28521:2009, hydraulic oil systems, pipe cleaning, flushing, grades of cleanliness, Reynolds number, flushing filters, leakage test, ship hydraulics.