01.04.2026

Rouging in pharmaceutical Water and Pure Steam Systems: Causes, Effects and Control Measures
[中譯] 藥用純水與純蒸氣系統之紅銹現象 (Rouging)：成因、影響與控制措施

In stainless steel pharmaceutical production facilities - particularly in water and steam systems - reddish-brown to black deposits occasionally appear on internal walls.
[中譯] 在不鏽鋼製藥生產設施中——特別是水系統與蒸氣系統——內壁偶爾會出現紅褐色至黑色的沉積物。

These discolorations are referred to as rouge or rouging. Purified Water (PW) and Water for Injection (WFI) systems, as well as steam systems, are typically affected.
[中譯] 這些變色現象被稱為紅銹 (Rouge 或 Rouging)。純水 (PW)、注射用水 (WFI) 以及蒸氣系統通常會受到影響。

Rouging also occurs in systems made of high-quality materials such as 316L.
[中譯] 即便是使用 316L 等高品質材料製造的系統，仍會發生紅銹現象。

The causes are oxidation processes or changes in the passive layer, in which iron components from the stainless steel react to form iron oxides/hydroxides and deposit on the surface.
[中譯] 其成因為氧化製程或鈍化層的變化，使不鏽鋼中的鐵成分反應形成氧化鐵/氫氧化鐵，並沉積於表面。

In practice, rouging typically manifests itself in water systems as a rub-off, reddish deposit.
[中譯] 在實務上，水系統中的紅銹通常表現為可擦拭的紅色沉積物。

In hotter steam systems, however, dark to black, firmly adhering deposits are more commonly found (often described as 'blacking').
[中譯] 然而在溫度較高的蒸氣系統中，更常見的是深色至黑色、牢固附著的沉積物（通常被稱為「黑化現象」）。

A common classification distinguishes between three classes: Class I as a wipeable, deposited corrosion deposit (without altering the underlying surface), Class II as an adherent corrosion product associated with insufficiently passivated surfaces, and Class III as a blue-black corrosion product (so-called magnetite), which typically forms in hot steam systems.
[中譯] 通用的分類將其分為三類：第一類為可擦拭的沉積型腐蝕沉積物（不改變底層表面）；第二類為與表面鈍化不足相關的附著型腐蝕產物；第三類則為通常在熱蒸氣系統中形成的藍黑色腐蝕產物（即所謂的磁鐵礦）。

Why does rouging occur - and why, in particular, in hot systems?
[中譯] 為何會發生紅銹——尤其是為什麼發生在高溫系統中？

The key factor is temperature: the hotter a system is operated or thermally sanitised, the more pronounced the rouging typically becomes.
[中譯] 關鍵因子是溫度：系統運行或熱滅菌的溫度越高，紅銹現象通常越明顯。

This is consistent with practical observations that rouging is virtually impossible to prevent entirely in systems stored at high temperatures or subjected to cyclic heating.
[中譯] 這與實務觀察一致，即在長時間保持高溫或承受週期性加熱的系統中，幾乎不可能完全防止紅銹。

At the same time, however, temperature control in water systems is a deliberate measure used to limit microbial growth.
[中譯] 但與此同時，水系統中的溫度控制是為了限制微生物生長而採取的必要手段。

The reason for the increased formation of rouging at higher temperatures is the shift in the water equilibrium (autoprotolysis) towards the ionic side with H3O+ and OH- ions at higher temperatures, whereby the hydronium ions represent the actual aggressive agent.
[中譯] 高溫下紅銹生成增加的原因，在於水的化學平衡（自解離作用）會向離子端（H3O+ 與 OH-）偏移，其中水合氫離子即為主要的侵蝕媒介。

In addition to temperature, the condition of the material plays a role.
[中譯] 除了溫度外，材料狀態也扮演重要角色。

Technical articles indicate that rouging is linked to a destabilisation of the passive layer and that measures such as passivation and electropolishing can reduce the risk or delay its onset, without being able to prevent rouging entirely.
[中譯] 技術文獻指出，紅銹與鈍化層的不穩定性有關，而鈍化處理 (Passivation) 與電解拋光 (Electropolishing) 等措施可降低風險或延緩其發生，但無法完全避免。

Operating conditions such as flow/standstill and system operation can also influence the rate of rouging formation.
[中譯] 運行條件（如流動/停滯狀態）以及系統操作方式也會影響紅銹的生成速率。

Is rouging 'merely visual' - or a quality risk?
[中譯] 紅銹只是「視覺問題」——還是「品質風險」？

Rouging is often first noticed visually and does not necessarily result in abnormal routine test parameters such as conductivity.
[中譯] 紅銹通常先經由視覺觀察發現，且未必會導致導電度 (Conductivity) 等常規檢測參數異常。

Rouging can become a concern if particles are introduced into the system and thus potentially into the product, or if even very small amounts of metal ions can affect a product's stability.
[中譯] 若微粒被引入系統進而進入產品中，或極微量的金屬離子影響了產品穩定性，紅銹就會成為重大疑慮。

For this reason, rouging is regularly inspected in practice, assessed as part of maintenance and addressed on a risk-based basis (e.g. with particular attention in biotechnological applications involving particle-sensitive steps).
[中譯] 因此，實務上會定期檢查紅銹，將其納入維護評估，並依據風險導向進行處理（例如在涉及微粒敏感步驟的生物技術應用中需特別注意）。

Levers for action in practice - what can be influenced?
[中譯] 實務應對槓桿——哪些是可以調整的？

The greatest scope for influence remains the operating and sanitisation temperature.
[中譯] 最具影響力的調整空間仍是運作與滅菌溫度。

Several sources discuss that thermal sanitisation does not necessarily have to be 'historically' set at 80 °C, but that - depending on design, 'cold spots' and validated efficacy - lower temperature ranges may be common and sufficient (frequently cited: temperatures above 65 °C).
[中譯] 多項資料指出，熱滅菌不一定必須遵循「慣例」設定在 80 °C；根據設計、冷點 (Cold spots) 及經過確效的有效性，較低的溫度區間可能更常見且足夠（常被引用的是 65 °C 以上）。

However, a reduction in temperature must be carefully planned and validated so as not to "trade off" rouging against microbiological risks (e.g. biofilm in colder areas).
[中譯] 然而，降低溫度必須經過縝密規劃與確效，以免為了解決紅銹而犧牲微生物風險控制（例如冷區產生的生物膜 Biofilm）。

Other influencing factors include the condition of the passive layer (passivation/electropolishing); furthermore, an overlay with nitrogen in tanks can exacerbate rouging.
[中譯] 其他影響因子包括鈍化層狀態（鈍化/電解拋光）；此外，儲槽中的氮氣覆蓋 (Nitrogen overlay) 可能會加劇紅銹。

Ozonisation, on the other hand, can counteract rouging. The reason for this is the oxidising effect of the oxygen, which contributes to the formation and maintenance of the passive layer.
[中譯] 另一方面，臭氧處理可以抵消紅銹。原因在於氧氣的氧化作用有助於鈍化層的形成與維持。

In practice, rouging is removed using de-rouging processes; however, experience shows that it reoccurs after a certain period of time.
[中譯] 在實務上會使用除銹 (Derouging) 程序，但經驗顯示紅銹在一段時間後仍會再次出現。

What is crucial, therefore, is not so much a 'one-off' removal, but rather a lifecycle approach: monitoring, risk analysis, targeted measures and - if necessary - derouging plus restoration of a suitable surface condition (e.g. passivation).
[中譯] 因此，關鍵不在於「一次性」的移除，而是生命週期管理：監控、風險分析、標靶措施，以及必要時的除銹加上表面狀態恢復（如鈍化處理）。

However, no chemical passivation processes are required to passivate stainless steel water distribution systems.
[中譯] 然而，不鏽鋼水分配系統的鈍化並不一定需要化學鈍化製程。

If the stainless steel surfaces are clean, passivation is achieved within a few minutes due to the oxygen content of the water medium.
[中譯] 若不鏽鋼表面保持清潔，透過水介質中的含氧量，在幾分鐘內即可達成自然鈍化。

Conclusion: Rouging cannot generally be completely prevented in hot pharmaceutical water and pure steam systems.
[中譯] 結論：在熱製藥用水與純蒸氣系統中，通常無法完全避免紅銹現象。

The most effective lever is temperature (operation/sanitisation) - though this is always in tension with microbiological control.
[中譯] 最有效的調整槓桿是溫度（運行/滅菌），儘管這始終與微生物控制處於權衡關係。

Passivation and electropolishing can reduce the risk, but they are no substitute for risk-based monitoring and a robust maintenance/sanitisation concept.
[中譯] 鈍化與電解拋光可降低風險，但無法取代風險導向的監控以及穩健的維護/滅菌方案。

Source: https://www.gmp-compliance.org/gmp-news/rouging-in-pharmaceutical-water-and-pure-steam-systems-causes-effects-and-control-measures