Microbially Influenced Corrosion (MIC) on Valve Body

Flanged 3" valve body after cross sectioning.

Observations

Pitting corrosion typical of microbiologically induced corrosion (MIC) was localized on one side of the valve body. It appears that most of the corrosion pits were inactive and filled with adherent oxide scale. The valve may have been closed for an extended time period, creating a localized stagnate low oxygen environment optimal for growth of sulfite reducing bacteria (SBR) resulting in severe MIC attack.

Material

ASTM A216 WCB

Chemistry

Carbon (max): .30

Manganese: 1 max

Phosphorus (max): .04

Sulfur (max): .05

Silicon: .10 – .35

Nickel (max): .40

Chromium (max): .30

Copper (max): .40

Columbium (max): .02

Vanadium (max): .08

Application

Upstream oil and gas process water transport lines.

Product

Cast steel valve body

Properties

Tensile Strength (ksi, min): 70 – 95

Yield Strength (ksi, min): 36

Elongation 2″ (% min): 22

Reduction Area (% min): 30

Hardness (HB, max): 187

 

Microstructures

Pearlitic and ferritic grain structured carbon steel