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Corrosion Under Insulation (CUI) Inspection

Corrosion Under Insulation (CUI) Inspection


Corrosion Under Insulation (CUI) is a serious type of localized external corrosion that takes place in carbon and low alloy steel equipment that is insulated. This category of corrosion happens when water is collected in or absorbed by the insulation, causing the equipment or the piping to corrode.

CUI is a comprehensive term which refers to many different forms of corrosion processes. As per the National Board of Boiler and Pressure Vessel Inspectors, the major CUI processes are categorized into several divisions, such as:

  • Galvanic
  • Alkaline/Acidic
  • Chloride
  1. Galvanic

    Results from wet insulation with an electrolyte or salt. It allows a current to flow between various metals (for instance, the insulated metal surface and the outer jacket). The extent and asperity of the attack on the less noble metal are based on the difference in potential between the two metals and their relative areas.

  2. Alkaline/Acidic

    Results from moisture and an alkali or acid in particular fibrous or granular insulations. In such situations, service temperatures surpass 121º C (250º F); most of the water evaporates at the edge of the insulation; and finally dissolves the alkaline or acidic chemicals there, resulting in corroding the jacket.

  3. Chloride

    Occurs on 300 - series austenitic stainless steel surfaces when the insulation consists of leachable chlorides and moisture at temperatures above 60º C (140º F). A concentration of chloride ions results from the evaporation of rain, water used in fighting fires, or process water.

Velosi Expertise and Methodology

Velosi offers best in class CUI Inspection services for our clients' refineries and process plants where equipment is usually operated at high temperatures in order to identify the presence of moisture within insulated vessels and pipelines.

We help our clients analyze CUI through:

  • Guided Waves (GW)
  • Pulsed Eddy Current (PEC)
  • Thermography
  • Real-Time Digital Radiography
  • Visual Examination

Velosi's unique Corrosion under Insulation (CUI) Inspection incorporate:

  1. PEC

    PEC equipment is dependent on electromagnetism and enables to determine effectively the Average Wall Thickness (AWT) of low-alloyed carbon steel components through their insulation, allowing the detection and localisation of CUI.

  2. GW

    Guided Waves measurement is one of the integral technologies for the evaluation of Corrosion Under Insulation (CUI) for long lengths of pipe.

  3. Real-Time Digitial Radiography

    This particular technology can make use of a radiation source and an X-ray detector (usually, a linear array of radiation detectors).

  4. Thermography

    Thermography and thermal imaging have been used in the petrochemical industry for monitoring system performance as well as the integrity of insulated pipelines and vessels for a long time.

  5. Visual Examination

    It is an effective process to locate CUI and it allows to identify potential CUI hazards emerged from damaged weatherproofing, cladding and/or insulation layers.

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