Process Piping Materials – Module 2 – M06-036

In CS, damage is often characterized by cup-shaped pits within pits and in austenitic stainless steel as subsurface cavities. Critical Factors to be considered with MIC include:

x Velocity – stagnant or low-flow conditions

x Temperature

x Oxygen Concentration

x Nutrients including inorganic substances (e.g. sulphur, ammonia, H2S) and organic substances (e.g. hydrocarbons, organic acids). In addition, all organisms require a source of carbon, nitrogen, and phosphorous for growth.

MIC has been found in heat exchangers, in the bottom of water storage tanks, piping with stagnant or low flow, and in piping in contact with some soils. Using well or ground water is especially susceptible to MIC contamination.

x Appropriate material selection, coating, chemical treatment (chlorine, bromine, ozone, ultraviolet light, or proprietary compounds) should be considered to minimize MIC.

x Bleach (NaOCl) is an effective biocide but must be used in the correct concentration (2 mg/l) to preclude damage to the MOC.

x A project hydrotest water quality specification should be issued for use during fabrication and construction, especially during hydrostatic tightness testing of equipment and piping.

x One of the most important steps is removal of water from equipment and equipment immediately after the hydro test followed by proper drying, preservation and capping.

x Using dry, oil free compressed air with a dew point of -40°F (-40°C) has been proven to be effective.

3.8.Applications for Cooling Water and Fire Water Systems

In Refineries, frequent failures have been experienced in cooling water and fire water services especially in the form of seam opening in ERW pipes.

It is recommended to use API 5L Gr. B standard pipes due to its mandatory requirement of NDT. The testing ensures improved weld quality and documentary evidence of Hydro test.

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