General Metal Loss FFS Calculation

Fitness for Service - General Metal Loss (Piping)

API 579-1 (2016) Part 4 Level 1 / 2 Assessment

Checklist

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

Metal loss has relatively smooth contours with no notches

Component is Type A Pipe , reducer conical section or elbow away from discontinuity (for separation criterion see 4.2.6(e))

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

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. If on an elbow then choose intrados or extrados (if full circ. metal loss then choose intrados); be careful selecting extrados as the calc is only valid for loss along a line at the outer radius of the bend - metal loss would normally extend further hence it would be more appropriate to select 'on straight'

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)

Corroded side

Length to major structural discontinuity, \(L_{msd}\) (mm) See 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 allowance (uniform), \(FCA\) (mm) Future corrosion in surrounding areas (internal + external). Used to calculate t_c for use in spacing criteria (fig 4.6) and averaging length (eq'n. 4.6). This could differ from FCA_ml if for instance only the defect area is re-coated.

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

Longitudinal average measured wall thickness, \(t^s_{am}\) (mm) If left blank this thickness will be assumed to be the same as the minimum measured thickness. Click the 'Check' button to find the length for thickness averaging. Averaging length, \(L\) (mm)click->

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

Longitudinal weld joint efficiency, \(E_L\)

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