Clean Steam / Pure Steam

Clean steam is generated from treated feedwater and carries no boiler additives, so its condensate meets water-for-injection quality. It is used wherever steam contacts product, product-contact surfaces or the sterilising environment — moist-heat sterilisation, sterilisation in place, and humidification of classified spaces — because plant steam carries corrosion inhibitors and amines that would deposit on those surfaces.

Its quality is characterised by three attributes that matter for sterilisation rather than for heating: non-condensable gases, which displace steam and prevent contact with the load; dryness, because entrained water carries energy without delivering latent heat where it is needed; and superheat, because steam that is hotter than saturation at that pressure behaves as dry gas and sterilises poorly. A steam system that meets chemical purity and fails these can still produce non-sterile loads.

The distribution system is part of the quality. Dead legs, inadequate slope, poor trapping and unsuitable materials degrade steam between generator and point of use, which is why sampling is performed at the point of use and not only at the generator.

• —Condensate meets water-for-injection quality; no boiler additives.
• —Used where steam contacts product, product-contact surfaces or the sterile environment.
• —Non-condensable gases, dryness and superheat govern sterilisation performance, separately from chemical purity.
• —Superheated steam behaves as a dry gas and sterilises poorly.
• —Sample at the point of use — distribution degrades steam quality.

Ph. Eur. and USP monographs for Water for Injection (condensate quality); EU GMP Annex 1 (2022); ISPE Baseline Guide Vol. 4 (Water and Steam Systems).