API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

RISK-BASED INSPECTION METHODOLOGY, PART 2, ANNEX 2.B—DETERMINATION OF CORROSION RATES 2.B-87
2.B.11.6
Tables
Table 2.B.11.1—Cooling Water Corrosion—Basic Data Required for Analysis: Recirculating
Cooling Water Systems and Once Through Cooling Water System with Fresh Water
Basic Data
Material of construction
Actual corrosion rates
Metal temperature of cooling or
condenser surfaces, (°C:°F)
pH a
pH s
TDS (mg/L)
Comments
Determine the material of construction of the equipment/piping. Only
carbon steel components are covered.
Corrosion coupon data on this system or similar systems or actual rates
at the facility. Caution is warranted when using corrosion rates as
determined from corrosion coupons or actual measured rates from
system measurements. These measurements may not be representative
or indicators of worst case. Example would be coupons placed in flowing
streams that could not provide data on for deposits or no flow areas.
Determine the estimated metal temperature exposed to the cooling
water, i.e. water-side metal surface temperature.
Experimentally measured pH of the water.
pH value at which the water is in equilibrium with solid calcium
carbonate (CaCO 3 ).
Determine if TDS is in the range of:
a) 50 to 400 mg/L, or
b) 401 to 1000 mg/L
Determine to what degree the TDS consist of salts (incl. ammonia),
phosphates, Cu, etc. that potentially effect under-deposit corrosion.
Ca (mg/L) as CaCO 3 Determine calcium hardness as calcium carbonate (CaCO 3 ).
Methyl orange alkalinity (mg/L) as CaCO 3
Flow velocity (m/s: ft/s)
Chlorides (ppm Cl − )
MIC observed or suspected? (Yes or No)
DO (ppm O 2 )
Corresponds to the concentration of bicarbonate (HCO 3 ), commonly
expressed as parts per million or mg/L of CaCO 3 (calcium carbonate).
Determine the maximum and minimum expected water velocities.
Determine parts per million of chlorides.
Indicate if MIC has been observed in the cooling water system, or if MIC
is considered likely.
Dissolved oxygen.
Table 2.B.11.2—Cooling Water Corrosion—Basic Data Required for Analysis: Once
Through Cooling Water System with Salt Water
Basic Data
Material of construction
Actual corrosion rates
Flow velocity (m/s:ft/s)
Comments
Determine the material of construction of the equipment/piping. Only carbon steel
components are covered.
Corrosion coupon data on this system or similar systems or actual rates at the facility.
Determine the maximum and minimum expected water velocities.