Home NI409 Guidelines for corrosion protection of seawater ballast tanks and hold spaces NI409 provides guidelines for corrosion protection of seawater ballast tanks and hold spaces on-board sea-going ship. ReferenceTitleDateNI409Guidelines for corrosion protection of seawater ballast tanks and hold spaces1995check related documents:NR467 Rules for the classification of steel shipsCheck other Bureau Veritas rules and guidelines.