Locally Thin Area FFS Calculation

Fitness for Service - Locally Thin Area (Piping)

API 579-1 (2016) Part 5 Level 1 Assessment

Checklist

Material is not operating in creep temperature range Minimum creep temperature 343C. Refer Table 4.11

Material has sufficient fracture toughness

Component is Type A Pipe , reducer conical section or elbow away from discontinuity. See 4.2.5(a)

External loads are low

Component is not in cyclic service

Input Data

required

Line number

Defect ID or Description

Inspection Report Number

Nominal diameter, \(DN\) (mm)

Schedule Nom. thickness, \(t_{nom}\) (mm)..

Custom nominal thickness, \(t_{nom}\) (mm) Only considered when Schedule is set to 'Custom'

Mill undertolerance (%) Set to zero or a positive number. If you have a directly measured uniform thickness reading, set this to zero and use the LOSS fields to adjust thickness OR use Custom nominal thickness.

Design temperature (C)

Allowable stress at design temperature, \(S\) (MPa)

'Y' factor, \(Y\) Eg. see ASME B31.1 Table 104.1.2(A) or ASME B31.3 Table 304.1.1

Design pressure, \(P\) (MPa(g))

Defect location If selecting reducer be mindful of L_msd check for knuckle. If on an elbow then choose intrados or extrados; be careful selecting extrados as the calc is only valid for loss along a line at the outer radius of the bend - otherwise choose 'on straight' if between extrados and centreline

Reducer angle, \(\alpha\) (degrees) Used only when 'reducer' selected

Bend radius, \(R_b\) (mm) Centreline radius of bend (used only when 'intrados' or 'extrados' selected)

Length to major structural discontinuity, \(L_{msd}\) (mm) See 4.2.6(e) and Figure 4.6

Uniform wall loss (external), \(LOSS_e\) (mm) External wall loss in surrounding areas

Uniform wall loss (internal), \(LOSS_i\) (mm) Internal wall loss in surrounding areas

Future corrosion allowance (external), \(FCA_{mle}\) (mm) Future corrosion in region of metal loss

Future corrosion allowance (internal), \(FCA_{mli}\) (mm) Future corrosion in region of metal loss

Future corrosion (uniform external), \(FCA_e\) (mm) Future corrosion in surrounding areas (external). Used to calculate corroded outer diameter and t_c for use in spacing criteria (fig 4.6). This could differ from FCA_mle if for instance only the defect area is re-coated.

Future corrosion (uniform internal), \(FCA_i\) (mm) Future corrosion in surrounding areas (internal). Used to calculate corroded inner diameter and t_c for use in spacing criteria (fig 4.6). This could differ from FCA_mli if for instance the defect area is preferentially attacked.

Minimum measured wall thickness, \(t_{mm}\) (mm) Minimum thickness within defect area

Wall thickness measurement tolerance, \(NDT_{tol}\) (mm) This will be subtracted from the minimum measured thickness. If you prefer you can set this to zero and alter the minimum thickness as required.

Longitudinal length of flaw, \(s\) (mm) Must account for adjacent defects per fig. 4.11. Also allow for projected future increase in length.

Circumferential length of flaw, \(c\) (mm) Must account for adjacent defects per fig. 4.11. Also allow for projected future increase in length.

Groove radius at base, \(g_r\) (mm) Enter estimated groove radius. If no groove then enter a relatively large number (in the order of wall thickness)

Longitudinal weld joint efficiency, \(E_L\) Required if damaged region is within the greater of 25.4mm or furnished plate thickness of weld centreline (ref. 2C.2.5a&b)

Circumferential weld joint efficiency, \(E_C\) Required if damaged region is within the greater of 25.4mm or furnished plate thickness of weld centreline (ref. 2C.2.5a&b)

Remaining strength factor allowed, \(RSF_a\) Factor comparing strength to original design Code. See clause 2.4.2.2(d)