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Corrosion Under Insulation (CUI)

CUI is corrosion phenomenon that occur beneath the piping insulator caused by the water ingress and  entrapment in the insulation.  The material suceptible to CUI is carbon steel, low alloy steel, 300 series SS, and duplex stainless steels. Based on the CUI tendency, it is usually occur in: 1) isolated pipe of steel carbon having operation temperature between - 4°C and 175°C, and 2) material austenitic stainless steelat operation temperature between 50°Cand 175°C. The corrosion rate increases with the following condition :

  1. Intermittent or variable (cyclic service) operation of equipment
  2. Temperature variations along the height or length of the equipment
  3. Temperature at which attachments to equipment operate; and
  4. Idle or mothballed conditions




Benefit of CUI

a. It decreases the likelihood of steam piping leaking.

b. Increase remaining life of the steam piping because the damage rate is identified.

c. Increase availability and decrease the un-planned shutdown.

d. Improve the safety of people and risk of the aging asset.

e. Promote risk based inspection, maintenance and repair of the asset.

f. Decrease the operation and maintenance cost because the inspection can be prioritized. 

g. Optimize the thermal and process efficiency since the steam quality (pressure, temperature and the enthalpy) is well                   maintained.