Calculate the general thinning Probability of Failure (PoF) for the top of deethanizer column based on the information and data given below. The equation to determine the PoF is given as

Pf(t) = gff x Df(t) x Fms

where, Pf(t) = Probability of failure gff = Generic failure frequency Df(t) = Damage factor Fms = Management system factor [assumed to be 1]

Information & Data

Equipment description: Column

Component type: Column Top

Operating temperature: 113 degree C

Operating pressure: 1338 kPa

Service start date: 2000

Material: SA 516-65

Service: Hydrocarbon with 3 mol% CO2 and 2 mol% H2S

Furnished thickness: 28 mm

Corrosion allowance (CA): 3.2 mm

pH: 5.5 7.5

Post weld heat treatment (PWHT): No

Insulation: Calcium silicate, average complexity and condition

Tmeasured = 24.79 mm

tmin = 24.26 mm

Measured corrosion rate = 5 mil per year (mpy)

Hardness < 200 BH The following inspections were completed four years ago:

General thinning; 2019 inspection effectiveness = 1C

Sulfide stress corrosion cracking (SSC); 2019 inspection effectiveness = 1C

Corrosion under insulation (CUI); 2019 inspection effectiveness = 1D

The Damage Factors for SSC and CUI are determined to be 5 and 4.7, respectively