API 579 FFS : SECTION 4Assessment of General Metal LossIssued January, 2000Prepared byDr. Mohammad Megahed

March 2004

Contents of Chapter-4 FFS

4.1. General4.2. Applicability and limitations of the Procedure4.3 Data Requirements4.4 Assessment Techniques and Acceptance Criteria 4.4.1 Overview 4.4.2 Level I Assessment 4.4.3 Level 2 Assessment 4.4.4 Level 3 Assessment4.5 Remaining Life Assessment 4.5.1 Thickness Approach 4.5.2 MAWP Approach4.6 Remediation4.7 In-Service Monitoring4.8 Documentation4.9 References4.10 Tables and FiguresExamples

4.1. GeneralFitness-For-Service (FFS) assessment procedures for pressurized components subject to general metal loss resulting from corrosion and/or erosion are provided in this section. The procedures can be used to qualify a component for continued operation or for re-rating as shown in the flow chart of Fig. 4.1

The procedures are based on a thickness averaging approachProvides a suitable result when applied to uniform metal loss. May produce conservative results if local areas of metal loss are present. FFS - Section 5 is used for cases of local metal loss For most evaluations, it is recommended to first perform an assessment using Section 4

4.2. Applicability and limitations of the Procedure

Section-4 can be used to evaluate all forms of general metal loss (uniform or local) which exceeds or is predicted to exceed the corrosion allowance before the next scheduled inspection.

The general metal loss may occur on the inside or outside of the component.

Assessment procedures based on thickness profiles and point thickness readings are provided.

The assessment procedure to be used depends on the type of thickness data available

Figure 4.2 illustrates the methodology used to determine the assessment procedure

Calculation methods are provided to rerate the component if the acceptance criteria are not satisfied.

Level 1 or 2 assessment procedures apply only if all of the following conditions are satisfied:

a. The original design criteria were in accordance with a recognized code or standard

b. The component is not operating in the creep range (see Table 4-1)

c. The region of metal loss has relatively smooth contours without notches

d. The component is not in cyclic service (less than 150 cycles)

e. The component does not contain crack-like flaws (Section -9 is used instead)

f. The component has a design equation which relates pressure to thickness

g. If the component does not have a design equation, assessment is limited to certain specified components

h. Some limitations on applied loads are satisfied

I. A flaw categorized as a groove should satisfy certain geometrical conditions

4.2.3.2.Level 3 Assessment can be performed when the Levels 1and 2 Assessment procedures do not apply. Examplesinclude, but are not limited to the following

a. Geometries associated with major structural discontinuities not covered In a Level 1 or Level 2 Assessment b. Components subject to supplemental loads not covered in the Level I or Level 2 assessment procedures.c. Components with a design based on proof testingd. Components operating in the creep rangee. Components in cyclic service or when fatigue analysis was performed in the original design calculations.

4.3 Data Requirements

4.3.1 Original Equipment Design Data4.3.2 Maintenance and Operational History4.3.3 Required Data/Measurements For A FFS Assessment

4.3.3.1 Thickness Readings a. Two options for obtaining thickness data are presented: (1) Individual point thickness readings (2) Thickness profiles (thickness readings on a prescribed grid).

Point thickness readings can be used to characterize the metal loss as general if there are no significant differences among the values obtained at inspection monitoring locations.

If there is a significant variation in the thickness readings, the metal loss may be localized, and thickness profiles should be used to characterize the remaining thickness and size of the region of metal loss.

b. The thickness quantities used in this section for the assessment of general metal loss are the average measured thickness and the minimum measured thickness. If the thickness readings indicate that the metal loss is general, the procedures in this section will provide an adequate assessment. However, if the metal loss is localized and thickness profiles are obtained, the assessment procedures of this section may produce conservative results, and the option for performing the evaluation using the assessment procedures of Section 5 is provided.

4.3.3.2 If point thickness readings are used in the assessment, theassumption of general metal loss should be confirmed.

a. Additional inspection may be required such as visual examination, radiography or other NDE methods.

b. A minimum of 15 thickness readings is recommended unless the level of NDE utilized can be used to confirm that the metal loss is general. In some cases, additional readings may be required based on the size of the component, the construction details utilized, and the nature of the environment resulting in the metal loss (Table 4.2).

c. If the Coefficient Of Variation (COV) of the thickness readings minus the Future Corrosion Allowance (FCA) is greater than 10%, then the use of thickness profiles should be considered for use in the assessment. The COV is defined as the standard deviation divided by the average (Table 4.3).

4.3.3.3 If thickness profiles are used in the assessment, the following procedure can be used to determine the required inspection locations and the Critical Thickness Profiles (CTP s).

Step 1:Locate the region of metal loss on the component and determine the location, orientation, and length of the inspection plane(s)

Step 1.1: To determine the inspection plane(s) for thickness readings the following should be considered:

a) Pressure Vessel Heads and Spheres (see Figure 4.3).

b) Cylindrical Shells, Conical Shells and Elbows (see Figure 4.4).

c) Atmospheric Storage Tanks (see Figure 4.5).

d) Low Pressure Storage Tanks

e) If the critical Inspection plane(s) for a component are not known at the time of the inspection, a minimum of two planes at right angles to each other should be utilized.

Step 1.2 Mark each Inspection plane on the component

Step 2- Determine the minimum required thickness, t (see Appendix A)

Step 3. Measure and record the wall thickness readings at Intervals along each inspection plane and determine the minimum measured wall thickness, tmin. If the corroded surface is not accessible for visual inspection, then the recommended spacing distance for thickness readings along each inspection plane Is given by the following equation; however, a minimum of five thickness readings is recommended for each inspection plane(s).

Ls = min [0.36Dtmin , 2tnom](4.1) ts = Recommended thickness profile spacing (mm:in), D = Inside diameter of the shell (mm: in), tnom = Nominal or furnished thickness of the component (mm:in) tmin = Minimum required thickness (mm:in).

Step 4. Determine the Critical Thickness Profile (CTP) in the meridional and circumferential directions, as shown in Figure 4.6. The length of the profile is established by determining the end point locations where the remaining wall thickness is greater than in the meridional and circumferential directions.

Note that the remaining wall thickness within the bounds of the CTP may exceed tmin. If there are multiple flaws in close proximity to one another, use the methodology shown in Figures 4.7, 4.8. For large regions of metal loss, more than one CTP may be utilized in the assessment.

4.3.3.4 If the region of metal loss is close to or at a major structural discontinuity, the remaining thickness can be established using the above procedures. However, additional thickness readings should be taken to include sufficient data points in the region close to the major structural discontinuity.

This involves taking adequate thickness readings within the zones defined as follows for the components listed below:

Nozzle or branch connection (see Figure 4.9 for the thickness zone, Lv, Lno, and Lni).

Conical shell transition (see Figure 4.10 for the thickness zone, Lv).

Axisymmetric discontinuities (see Figure 4.11 for the thickness zone, Lv).

Flange connections (see Figure 4.12 for the thickness zone, Lvh and Lvt).

4.3.4 Recommendations For Inspection Technique and Sizing Requirements

4.3.4.1 Thickness readings are usually made using straight beam ultrasonic thickness examination (UT).4.3.4.2 Obtaining accurate thickness readings using UT is highly dependent on the surface condition of the component.4.3.4.3 All UT thickness readings should be made after proper calibration for the wall thickness and temperature 4.3.4.4 Radiographic examination (RT) may also be used to determine metal loss

4.4 Assessment Techniques and Acceptance Criteria

4.4.1 Overview

4.4.1.1 If the metal loss is less than the specified corrosion/erosion allowance and adequate thickness is available for the future corrosion allowance, no further action is required other than to record the data; otherwise, an assessment is required.

4.4.1.2 An overview of the assessment levels is provided in Figure 4.1.

Level 1 Assessments are limited to components which have a design equation which specifically relates pressure (or liquid fill height for tanks) and/or other loadings, as applicable, to a required wall thickness. Level 2 Assessments can be used to evaluate components which do not satisfy Level 1 criteria, and can also be used to evaluate components which do not have a design equation which specifically relates pressure to a required wall thickness. For example, the design rules for nozzle reinforcement in the ASME Code, Section VIII, Division I are provided in terms of reinforcement areas which result in a thickness Interdependency between the required thickness of the shell and nozzle. Level 3 assessments can be used to evaluate components which are not covered or do not pass a Level I or Level 2 assessment.

4.4.1.3 If the thickness readings indicate that the metal loss is localized and thickness profiles are obtained, the assessment procedures of this section can still be used for the assessment However, the results may be conservative, and the option for performing the analysis using the assessment procedures of Section 5 is provided.

4.4.1.4FFS assessments for the components listed below require special consideration because of the complexities associated with the design requirements of the original construction code. a. Pressure Vessels Designed To The ASME Code, Section VIII, Division 2b. Low Pressure Storage Tanks Designed To API 620c. Piping Designed To ASME B31.3

4.4.2 Level I Assessment

4.4.2.1 The following assessment procedure can be used. If the flaw is found to be unacceptable, the procedure can be used to establish a new MAWP or MFH.

Step 1. Determine the minimum required thickness, tmin (see Appendix A, paragraph A.2).

Step 2. Locate regions of metal loss on the component and determine the type of thickness data that will be recorded; point thickness readings or thickness profile data. Based on these data, determine the minimum measured thickness, t If thickness profile data are used, then proceed to Step 3. If point thickness readings are used, determine the Coefficient of Variation (COV) based on the thickness readings and Future Corrosion Allowance. If the COV is less than or equal to 10%, then proceed to Step 6 to complete the assessment using the average thickness, tam. If the COV is greater than 10%, then use of thickness profiles should be considered for the assessment, or a Level 3 Assessment can be performed.

Step 3. Determine the length for thickness averaging, L.Step 3.1. Compute the remaining thickness ratio, Rt =( tmm-FCA) /tmin

FCA =Future corrosion allowance (mm:in),tmin = Minimum required thickness (mm:in), tmm =Minimum measured thickness (mm:in).

Step 3.2. Compute the length for thickness averaging, L = QDtmin(4.3) D = Inside diameter of the cylinder (or equivalent for other geometries Q = Factor from Table 4.4 based on an allowable Remaining Strength Factor and Rt

Step 4. Establish the Critical Thickness Profiles (CTPs) from the thickness profile data, and determine s and c Step 5. Based on the parameters L and s from Steps 3 and 4, respectively, perform the FFS assessment of the region of metal loss using one of the following methods:

For (sL) The meridional or longitudinal extent of metal loss is acceptable If the limiting flaw size criteria In Section 5, paragraph 5.4.2.2.d are satisfied. For spherical shells, formed heads and atmospheric storage tanks the assessment is complete. For cylindrical shells, conical shells and elbows, the circumferential extent of the metal loss must be checked using Section 5, paragraph 5.4.2.2.g to complete the assessment

For (s>L)

One of the following assessment methods may be used:a) Set the average thickness equal to the measured minimum thickness, or tam=tmm) and proceed to Step 6. b) Determine the average and minimum measured thickness for the meridional and circumferential CTP s as described below, then proceed to Step 6.1) Determine tmm (minimum measured thickness) considering all points on longitudinal and circumferential CTP's .2) Compute the average measured thickness from the CTP in the meridional and circumferential directions and designate these values as tams and tamc respectively. The average thickness is computed by numerically averaging the thickness readings over length L. The center or midpoint of the length for thickness averaging, L, should be located at tmm3) For cylindrical and conical shells and pipe bends, tam = tams in a Level 1 Assessment. In a Level 2 Assessment, tams and tamc are used directly in the assessment to account for supplemental loads.

4) For spheres and formed heads tam = min [tams, tamc] in a Level 1 or 2 Assessment.c) The region of metal loss can be evaluated using a Level 3 Assessment.d) The region of metal loss can be evaluated using the Section 5 Assessment procedures for local metal loss.

Step 6. The acceptability for continued operation can be established using the following criteria.The average measured wall thickness should satisfy tam FCA tmin (eq.4.4). Alternatively, MAWP or MFH calculated based on the thickness (tam FCA) should be equal to or greater than the current MAWP or maximum design liquid level, respectively.The minimum measured wall thickness, tmm should satisfy the following thickness criterion.

For pressure vessels and piping systems, tmm - FCA max [0.5tmin, 2.5 mm (0.10 inches)] (4.5)

For atmospheric storage tanks, tmm - FCA max [0.6tmin, 2.5 mm (0.10 inches)](4.6)

4.4.2.2 If the component does not meet Level I Assessment requirements, then the following, or combinations thereof, can be considered:a. Rerate, repair, replace, or retire the component.b. Adjust the FCA by applying remediation techniques (see paragraph 4.6).c. Adjust the weld joint efficiency or quality factor, E, by conducting additional examination and repeat the assessment (Note: To raise the value of E from 0.7 to .85, or from .85 to 1.0, would require that the weld seams be spot or 100% radiographed, respectively, and the examinations may reveal additional flaws that will have to be evaluated).d. Conduct a Level 2 or Level 3 Assessment.

4.4.3 Level 2 Assessment

4.4.3.1 The Level 2 assessment procedure can be used to evaluate components described in paragraphs 4.2.3.1 .f and 4.2.3.1 .g subject to the loads defined in paragraph 4.2.3.1 .h. If the flaw is found to be unacceptable, the procedure can be used to establish a new MAWP or MFH.

4.4.3.2 Step 1. Calculate the thickness required for supplemental loads, tsl and the minimum required thickness tmin

Step 2. Locate regions of metal loss and determine the type of thickness data that will be recorded. Determine the minimum measured thickness, tmm. If thickness profile data are used, then proceed to Step 3. If point thickness readings are used, then complete the assessment following the methodology in paragraph 4.4.2.1 .b.

Step 3. Determine the length for thickness averaging, L (see paragraph 4.4.2.1.c).

Step 4. Establish the Critical Thickness Profiles (CTPs) and determine s and c (see paragraph 4.4.2.1 .d).

Step 5. Perform the FFS assessment using one of the methods in paragraph 4.4.2.1.e.

Step 6. The acceptability for continued operation can be established using the following criteria.

1. Pressure Vessels and Piping Systemsa) The average measured wall thickness for the CTP(s) should satisfy the following thickness criteria. Alternatively, the M WI calculated based on the thicknesses (tam-FCA)/RSFa and (tam - FCA - tsl)/RSFa (see Appendix A) should be equal to or exceed the design MAWP. The allowable remaining strength factor, RSFa, can be determined from Section 2.

1)Cylindrical and Conical Shells:tams-FCA RSFa * tcmin(4.7)

tamc-FCA RSFa * tLmin(4.8)

2)Spherical Shells and Formed Heads:tam-FCA RSFa * tmin(4.9)

b) The minimum measured wall thickness, tmm for the CTP(s) should satisfy the criterion in paragraph 4.4.2.1f.2.

2. Shell Courses of API 650 Storage Tanks The requirements are the same as for Level 1 (see paragraph 4.4.2.1.f) because of the higher allowable stress permitted for in- service tankage as stipulated in API 653.

4.4.3.3 The following assessment procedure can be used to evaluate components described in paragraph 4.2.3.1 .g subject to the loads defined in paragraph 4.2.3.1 .h.

a. Design rules for components at a major structural discontinuity typically involve the satisfaction of a local reinforcement requirement (e.g. nozzle reinforcement area), or necessitates the computation of a stress level based upon a given load condition and geometry and thickness configuration (e.g. flange design). These rules typically result in one component with a thickness which is dependent upon that of another component (for examples, see paragraph 4.2.3.1 .g). Design rules of this type have thickness interdependency, and the definition of a minimum thickness for a component is ambiguous.

b. To evaluate components with a thickness interdependency, the MAWP should be computed based upon the average measured thickness minus the future corrosion allowance (tam- FCA) and the thickness required for supplemental loads (see Appendix A, paragraph A.2.6) for each component using the equations in the original construction. The calculated MAWP should be equal to or exceed the design MAWP.

c. The average thickness of the region, tam can be obtained as follows for components with a thickness interdependency:1. Nozzles and branch connections Determine the average thickness within the nozzle reinforcement zone shown in Figure 4.9 (see paragraph 4.3.3.4). The assessment procedures In Appendix A, paragraphs A.3.1 I and A.5.7 can be utilized to evaluate metal loss at a nozzle or piping branch connection, respectively. The weld load path analysis in this paragraph should also be checked, particularly if the metal loss has occurred in the weldments of the connection.

2. Axisymmetric Structural Discontinuities Determine L using the procedure in paragraph 4.4.2.1.c and Lv based on the type of structural discontinuity listed below. The average thickness is computed based on the smaller of these two distances. If L < Lv the midpoint of L should be located at tmm to establish a length for thickness averaging unless the location of tmm, is within L/2 of the zone for thickness averaging. In this case, L should be positioned so that it is entirely within Lv before the average thickness is computed.

Conical shell transition (see Figure 4.10 for the zone for thickness averaging and Lv).

Axisymmetric discontinuities (see Figure 4.11 for the zone for thickness averaging and Lv).

Flange connections (see Figure 4.12 for the zone for thickness averaging and Lv).

3. Piping Systems Piping systems have a thickness interdependency because of the relationship between the component thickness, piping flexibility, and the resulting stress.

For straight sections of piping, determine L using the procedure in paragraph 4.4.2.1 .c and compute the average thickness to represent the section of pipe with metal loss in the piping analysis. For elbows or bends, the thickness readings should be averaged within the bend and a single thickness used in the piping analysis (i.e. to compute the flexibility factor, system stiffness and stress intensification factor). For branch connections, the thickness should be averaged within the reinforcement zones for the branch and header, and these thicknesses should be used in the piping model (to compute the stress intensification factor). An alternative assumption is to use the minimum measured thickness to represent the component thickness in the piping model. This approach may be warranted if the metal loss is localized; however, this may result in an overly conservative evaluation. In these cases, a Level 3 assessment may be required to reduce the conservatism in the assessment (see paragraph 4.4.4.4).

d. The minimum measured wall thickness, t, should satisfy the criterion in paragraph 4.4.2.1 .f.2.

4.4.3.4 If the component does not meet the Level 2 Assessment requirements, then the following, or combinations thereof, can be considered:

a. Rerate, repair, replace, or retire the component.

b. Adjust the FCA by applying remediation techniques (see paragraph 4.6).

c. Adjust the weld joint efficiency factor, E, by conducting additional examination and repeat the assessment (see paragraph 4.4.2.2.c).

d. Conduct a Level 3 Assessment.

4.4.4 Level 3 Assessment

4.4.4.1 The stress analysis techniques discussed in Appendix B can be utilized to evaluate regions of general or local metal loss in pressure vessels, piping, and tanks. The finite element method is typically used to compute the stresses in a component however, other numerical methods such as the boundaty element or finite difference method may also be used. Handbook solutions may also be used if the solution matches the component geometry and loading condition. The evaluation may be based on a linear stress analysis with acceptability determined using stress categorization, or a nonlinear stress analysis with acceptability determined using a plastic collapse load. Nonlinear stress analysis techniques are recommended to provide the best estimate of the acceptable load carrying capacity of the component. Guidelines for performing and processing results from a finite element analysis for a fitness-for-service analysis are provided In Appendix B.

4.4.4.2 If a component Is subject to external pressure andlor other loads which result In compressive stresses, a structural stability analysis should be performed using the methods in Appendix B to determine suitability for continued service. In addition, methods to evaluate fatigue are also induded in Appendix B If a component is subject to cyclic loading.

4.4.4.3 Thickness data per paragraphs 4.3.3 as well as the component geometry, matenal properties and loading conditions are required for a Level 3 Assessment. The thickness data can be used directly in finite element model of the component. If thickness profile data are available, the thickness grid can be directly mapped Into a three dimensional finite element model using two or three dimensional continuum elements, as applicable. This information can also be used If the component is modeled using shell elements.

4.4.4.4 If the region of local metal loss is close to or at a major structural discontinuity, details of the component geometry, material properties, and imposed supplemental loads (see Appendix A, paragraph A.2.6) at this location are required for the assessment. Special consideration is required if there are significant supplemental loads at a nozzle, piping branch connection, or pipe bend. The location and distribution of the metal loss in these components may significantly effect both the flexibility and stress distribution in a manner that cannot be evaluated using the approaches employed in the design. In addition, the localized metal loss may significantly reduce the plastic collapse load capability depending on the nozzle geometry, piping system configuration, and/or applied supplemental loads.

4.5 Remaining Life Assessment

4.5.1 Thickness Approach4.5.1.1 The remaining life of a component may be determined based upon computation of a minimum required thickness for the intended service conditions, thickness measurements from an inspection, and an estimate of the anticipated corrosion rate. This method is suitable for determination of the remaining life if the component does not have a thickness interdependency (see paragraph 4.4.3.3.a).Rlife = (tam Ktmin)/Crate (4.10)where,C=Anticipated future corrosion rate (mm/year:inlyear),K=Factor depending on the assessment level; for a Level 1 assessment K = 1.0, for a Level 2 Assessment; K = RSFa for pressure vessels and piping components and K = 1.0 for shell courses of tanks,Rlife =Remaining life (years),RSFa =Allowable remaining strength factor (see Section 2), tam = Average wall thickness of the component determined at the time of the inspection (mm:in), andtmin=Minimum required wall thickness, t , of the component (see Appendix A, paragraph A.2).

4.5.1.2 The remaining life determined using the thickness based approach may produce non-conservative results when applied to components which have a thickness dependency (see paragraph 4.4.3.3.a). For these cases, the remaining life should be established using the MAWP Approach.

4.5.2 MAWP Approach

4.5.2.1 The MA WP approach provides a systematic way of determining the remaining life of any pressurized component. This method is also the only method suitable for determining the remaining life of components with a thickness dependency. In addition, the MAWP approach ensures that the design pressure is not exceeded during normal operation if the future corrosion rate is appropriately established.

4.5.2.2 The following procedure can be used to determine the remaining life of a component using the MA WP approach:

Step 1 Determine the metal loss of the component, tloss, by subtracting the average measured thickness from the time of the last inspection, tam, from the nominal thickness, tnom

Step 2 Determine the MAWP for a series of increasing time increments using an effective corrosion allowance and the nominal thickness in the computation.

The effective corrosion allowance is determined as follows: CAe =tloss + Crate * time (4.11)where,Crate = Anticipated future corrosion rate (mm/year:in/year), CAe = Effective corrosion allowance (mm:in),tloss = Metal loss, defined as (tnom tam) (mm:in),tnom = Nominal or furnished wall thickness of the component (mm:in),tam = Average wall thickness of the component determined at the time of the inspection (mm:in), andtime = Time in the future (years).

Step 3 Determine the remaining life from a plot of the MAWP versus time. The time at which the MA WP curve intersects the design MAWP for the component is the remaining life of the component.

Step 4 Repeat the Steps 1, 2 and 3 for each component. The equipment remaining life is taken as the smallest value of the remaining lives computed for each of the individual components.

4.5.2.3 This approach may also be applied to tanks using the maximum fill height, MFH, instead of the MAWP.

4.6 Remediation4.6.3 Remediation Method 1:

Performing Physical Changes to the Process Stream:a. Increasing or decreasing the process temperature and/or pressure b. Increasing or decreasing the velocity of the stream c. Installing scrubbers, treaters, coalescers and filters to remove certain fractions

4.6.4 Remediation Method 2 Application of solid barrier linings or coatings to keep the environment isolated from the base metal, which has suffered previous damage.

4.6.4.1 Organic coatings a. Thin film coatingsb. Thick film coatings

4.6.4.2 Metallic linings These fall into three general classes:

a. Metal spray linings b. Strip linings c. Weld overlay

4.6.4.3 Refractory linings

4.6.5 Remediation Method 3 Injection of water and/or chemicals on a continuous basis to modify the environment or the surface of the metal. a. Water washing to dilute contaminants

b. Injection of chemicals to change the aggressiveness of the solution

c. Injection of filming type chemicals to coat the metal surface

4.6.6 Remediation Method 4.- Application of weld overlay

4.7 In-Service Monitoring

4.7.1 Mitigation methods can be applied, but in some cases these are not feasible 4.7.2 Typical monitoring methods include the use of the following tools or procedures:

Corrosion probesHydrogen probesRetractable corrosion coupons and physical probesUT measurements and scanningRadiographic examinationStream samples for H2S, Cl, NH3, Co2 , Fe, Ni, pH, water content, Hg, etc.Infrared thermographyThermocouples

4.8 Documentation

4.8.1 The documentation of the FFS Assessment should include the information cited in Section 2, paragraph 2.8.

4.8.2 Inspection data including all thickness readings and corresponding locations used to determine the average measured thickness, t and the minimum measured thickness, t should be recorded and included in the documentation. A sample data sheet Is provided in Table 4.1 for this purpose. A sketch showing the location and orientation of the inspection planes on the component is also recommended.

4.9 ReferencesOsage, D.A., Buchheim, G.M., Brown, R.G., Poremba, J., An Alternate Approach for InspectionScheduling Using the Maximum Allowable Working Pressure for Pressurized Equipment, ASMEPVP-VoI. 288, American Society of Mechanical Engineers, New York, 1994, pp. 261-273.Tables and FiguresSolved Examples