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. Reference Title Date NI409 Guidelines for corrosion protection of seawater ballast tanks and hold spaces 1995 check related documents: NR467 Rules for the classification of steel ships Check other Bureau Veritas rules and guidelines.