{"id":6973,"date":"2026-05-08T12:54:57","date_gmt":"2026-05-08T12:54:57","guid":{"rendered":"https:\/\/www.airvision.be\/?p=6973"},"modified":"2026-05-08T12:57:19","modified_gmt":"2026-05-08T12:57:19","slug":"aandachtspunten-3-vochtigheid-dauwpunt","status":"publish","type":"post","link":"https:\/\/www.airvision.be\/en\/aandachtspunten-3-vochtigheid-dauwpunt\/","title":{"rendered":"Pitfalls #3 – Humidity & dew point"},"content":{"rendered":"\n

Humidity & dew point: “it’s hot \u2260 no moisture”<\/h2>\n\n\n\n
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“The gas is at 180\u00b0C \u2014 there can’t be any condensation.”<\/strong><\/p>\n\n\n\n

This assumption is commonly made. And commonly wrong.
A gas temperature tells you nothing about its moisture content. A hot gas can be perfectly saturated with water vapour. It’s the temperature relative to the dew point that determines whether that vapour stays gaseous \u2014 or condenses.<\/p>\n<\/div>\n<\/div>\n\n\n\n

The transient regime trap<\/strong>
The problem generally doesn’t occur under steady-state conditions.
At 180\u00b0C, if the dew point of the gas is around 60\u00b0C, everything is fine. But at start-up, shutdown, or during a load reduction, the temperature drops. If it falls below the dew point, condensation appears \u2014 sometimes localised, on the cold walls of the casing, on the shaft, in the upstream or downstream ductwork.
And if the gas contains SO\u2082, HCl, or other acidic compounds, that condensation doesn’t produce water \u2014 it produces acid. The resulting corrosion can be rapid and severe, well beyond what a simple 304 stainless steel selection can handle.<\/p>\n\n\n\n

What we check at AirVision<\/strong>
When a request involves hot gases with a process origin \u2014 combustion fumes, drying effluents, industrial process gases \u2014 we systematically ask about the dew point, not just the nominal temperature.
This determines:<\/p>\n\n\n\n

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  • the choice of materials (from carbon steel to alloyed refractory steels, depending on the aggressiveness of the condensate),<\/li>\n\n\n\n
  • whether heat tracing or insulation of cold zones is required,<\/li>\n\n\n\n
  • the identification of thermal bridges in the circuit \u2014 a poorly insulated zone or an untreated metal contact can be enough to locally drop the temperature below the dew point, even when the gas is globally hot.<\/li>\n\n\n\n
  • and sometimes the positioning of the fan itself within the circuit, to avoid exposure to critical cold-start phases.<\/li>\n<\/ul>\n\n\n\n

    Key takeaway<\/strong>
    A hot gas can be humid. A humid gas can condense at start-up or shutdown. And if that gas is acidic, transient condensation is enough to permanently damage the equipment.
    Nominal operating temperature is a starting point \u2014 not a guarantee that condensation is absent.<\/p>\n","protected":false},"excerpt":{"rendered":"

    Humidity & dew point: “it’s hot \u2260 no moisture” “The gas is at 180\u00b0C \u2014 there can’t be any condensation.” This assumption is commonly made. And commonly wrong.A gas temperature […]<\/p>\n","protected":false},"author":3,"featured_media":6971,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-6973","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-technical-articles"],"_links":{"self":[{"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/posts\/6973","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/comments?post=6973"}],"version-history":[{"count":2,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/posts\/6973\/revisions"}],"predecessor-version":[{"id":6980,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/posts\/6973\/revisions\/6980"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/media\/6971"}],"wp:attachment":[{"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/media?parent=6973"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/categories?post=6973"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.airvision.be\/en\/wp-json\/wp\/v2\/tags?post=6973"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}