{"id":17897,"date":"2026-10-19T10:54:34","date_gmt":"2026-10-19T08:54:34","guid":{"rendered":"https:\/\/consilab.de\/?p=17897"},"modified":"2026-10-19T10:54:34","modified_gmt":"2026-10-19T08:54:34","slug":"consiletter-8","status":"publish","type":"post","link":"https:\/\/consilab.de\/en\/consiletter-8\/","title":{"rendered":"consiLetter 8: Two-phase flow through safety valves \u2013 what needs to be done?"},"content":{"rendered":"

[vc_row rt_row_background_width=”fullwidth” rt_row_content_width=”default” rt_row_style=”default-style” rt_row_borders=”” rt_row_shadows=”” rt_row_paddings=”true” rt_bg_effect=”classic” rt_bg_image_repeat=”repeat” rt_bg_size=”cover” rt_bg_position=”right top” rt_bg_attachment=”scroll” rt_bg_video_format=”self-hosted” class=”with_sidebar”][vc_column width=”1\/4″ rt_column_shadow=”” rt_bg_image_repeat=”repeat” rt_bg_size=”auto auto” rt_bg_attachment=”scroll” css=”.vc_custom_1782376114778{padding-top: 0px !important;}” rt_bg_color=”” rt_bg_overlay_color=””][vc_widget_sidebar sidebar_id=”ca-sidebar-15951″ el_class=”consiletter__sidebar”][\/vc_column][vc_column width=”3\/4″ rt_column_shadow=”” rt_bg_image_repeat=”repeat” rt_bg_size=”auto auto” rt_bg_attachment=”scroll” css=”.vc_custom_1782378935763{padding-top: 0px !important;}” rt_bg_color=”” rt_bg_overlay_color=”” class=”consiletter__letter”][vc_column_text css=””]consiletter 8<\/strong><\/p>\n

Two-phase flow through safety valves \u2013 what needs to be done?<\/h1>\n

During quick relief of a pressurized container using a release line located on the vapor space side, a rupture disk or a safety valve, a surge of the bubbling liquid may lead to a two-phase flow of vapor and accompanying liquid. Gas dissolved in the liquid may also be released by the discharge of pressure and cause a full surge \u2013 as when opening a champagne glass, when carbon dioxide bubbles suddenly form and push the liquid out of the bottle.<\/p>\n

Two-phase flow<\/a> that may be caused by a surge leads to the following challenges:<\/p>\n

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  1. The accompanying liquid can be released into the surroundings, which in the case of flammable or toxic substances can be particularly critical. To avoid the release of liquids into the environment, liquid separators, e. g. cyclone separators, should be used for all flammable or toxic substances.<\/li>\n
  2. Pressure loss in the pressure relief line system is increased by the liquid. In some cases, the liquid may also accumulate and the developing plug flow can cause pressure surges. Pressure loss in the pressure relief line during a two-phase flow must be considered in the sizing.<\/li>\n
  3. The liquid blocks a part of the relieving opening, which reduces the mass flow of gas through which the majority of energy is carried out of the vessel in the form of evaporation heat. To compensate for the equal increase in pressure in the vessel, a greater relief cross-section is required than is the case with a pure gas flow. The sizing of safety valves for two-phase flows has been governed since October 2010 by the international standard ISO 4126 part 10, which in particular takes into account the conditions in the chemical industry.<\/li>\n<\/ol>\n