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RBI 581

Oleh:

Dr. Ir. Haryadi

Development of Inspection Programs to Reduce Risk

JURUSAN TEKNIK MESINPOLITEKNIK NEGERI BANDUNG

2014

Introduction

Development of Inspection Programs:

that address the types of damage that inspection should

detect, and the appropriateinspection techniques to

detect the damage.

Reducing Risk Through Inspection:

discusses the application of Risk-Based Inspection tools to

reduce risk and optimize inspection programs.

Approach To Inspection Planning

Contains

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1. INTRODUCTION1. INTRODUCTION1. INTRODUCTION1. INTRODUCTION

The probability of failure due to progressive damage is a

function of four factors:

Damage mechanism and resulting type of damage

(cracking, thinning, etc.).

Rate of damage progression.

Probability of detecting damage and predicting future

damage states with inspection technique(s).

Tolerance of the equipment to the type of damage.

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2. 2. 2. 2. DEVELOPMENT OF INSPECTION DEVELOPMENT OF INSPECTION DEVELOPMENT OF INSPECTION DEVELOPMENT OF INSPECTION

PROGRAMSPROGRAMSPROGRAMSPROGRAMS

An inspection program is developed by systematically

identifying:

a. What type of damage to look for.

b. Where to look for it.

c. How to look for the damage (what inspection

technique).

d. When (or how often) to look.

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Design and construction data:

a. Equipment type (heat, mass, or momentum transfer) and function (shell and tube exchanger, trayed distillation column, centrifugal pump, etc.).

b. Material of construction.

c. Heat treatment.

d. Thickness.

Process data, including changes:

a. Temperature.

b. Pressure.

c. Chemical service, including trace components (such as chlorides, CNs,ammonium salts, etc.).

d. Flow rate.

Equipment history:

a. Previous inspection data.

b. Failure analysis.

c. Maintenance activity.

d. Replacement information.

Data

Inspection techniques are selected based on their ability to find the

damage type; however, the mechanism that caused the damage

can affect the inspection technique selection.

Table 9-7 qualitatively lists the effectiveness of inspection

techniques for each damage type listed in Table 9-2.

A range of effectiveness is given for some damage type/inspection

technique combinations based on comments from various sources,

including the API Subcommittee on Inspection.

Selection of the inspection technique will depend on not only the

effectiveness of the method, but on equipment availability and

whether or not an internal inspection can be made.

2.2 How To Look For Damage (Inspection2.2 How To Look For Damage (Inspection2.2 How To Look For Damage (Inspection2.2 How To Look For Damage (Inspection

Technique)Technique)Technique)Technique)

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Damage types are the physical characteristics of damage that

can be detected by an inspection technique.

Damage mechanisms are the corrosion or mechanical actions

that produce the damage.

Table 9-1 describes damage types and their characteristics.

Tables 9-2 through 9-6 list damage mechanisms by broad

categories.

The types of damage that can be associated with them are

also listed.

These lists of damage mechanisms were developed by several

API members of the Fitness for Service Program.

2.1 What Type of Damage To Look For and2.1 What Type of Damage To Look For and2.1 What Type of Damage To Look For and2.1 What Type of Damage To Look For and

Where To LookWhere To LookWhere To LookWhere To Look

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3. REDUCING RISK THROUGH 3. REDUCING RISK THROUGH 3. REDUCING RISK THROUGH 3. REDUCING RISK THROUGH

INSPECTIONINSPECTIONINSPECTIONINSPECTION

In this case study, a usually effective inspection was

performed after six years.

For the following analysis, it is assumed that the inspection

revealed an actual corrosion rate of 5 mpy vs. the predicted

rate of 10 mpy.

Figure 9-3 shows the damage subfactor table from the

technical module for general corrosion. The thick line on the

table shows the path traced by an inspection plan (this is

discussed further in the next section). Using Table 9-19, the

following steps show how the damage subfactor is calculated

for the risk assessment.

3.1 Measuring Risk Associated With Existing3.1 Measuring Risk Associated With Existing3.1 Measuring Risk Associated With Existing3.1 Measuring Risk Associated With Existing

Inspection SystemInspection SystemInspection SystemInspection System

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Step 1: Calculate the ratio ar/t.

This is the equipment age (or time in current service) (a) times the corrosion rate (r), in in./yr, divided by the original thickness (or thickness at time equipment went into current service) (t).

Example:

5 mpy (0.005 in./yr), 6 years old, original thickness 0.375 in. ar/t = 6 x 0.005/0.375 = 0.08.

Step 2: Determine the overdesign factor.

This is a correction factor selected from the table in Table 9-12 that will be applied to the damage subfactor. The correction is necessary because the subfactors from the table arebased on a vessel that has a corrosion allowance of 25% of the wall thickness, while the vessel in this example has a corrosion allowance of 50% of the wall thickness. Vessels with a greater corrosion allowance should have a lower damage subfactor, while those with less corrosion allowance should have a higher damage subfactor.

Example:

Original thickness = 0.375 in.,

Corrosion allowance = 0.1875.

tactual / (tactual Corrosion Allowance) = 0.375 / 0.1875 = 2.0.

The overdesign factor selected from the table, is 0.5; that is, the damage subfactors are to be multiplied by one-half (for subfactors greater than 1).

Step 3: Refer to Figure 9-3 to find the damage subfactor for this vessel.

At one inspection (of any effectiveness) and ar/t = 0.08, the damage subfactor is 1.

Step 4: Multiply results of Step 3 by results of Step 2.

APPROACH TO INSPECTION PLANNINGAPPROACH TO INSPECTION PLANNINGAPPROACH TO INSPECTION PLANNINGAPPROACH TO INSPECTION PLANNING

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Implicit in the ar/t lookup tables is a remaining life.

When the damage factor rises to 10 or higher with 4 or more highly effective inspections, then the equipment is at or near the end of its life. In other words, there have been enough inspections to have relative certainty about the corrosion rate, and additional inspections no longer improve the damage factor.

The inspection planning method solves for the number of years at which this point occurs (roughly ar/t = 0.4, with corrections for pressure and corrosion allowance).

If this value is one year or less, a diagnostics module is called to provide a warning that based on the entered corrosion rate, age, and number of inspections, the equipment is already at or near its end of life. Careful data checking and/or confirmation of equipment condition are recommended.

If the remaining life is greater than one year, determine the number of inspections needed to achieve a high confidence in the corrosion rate over the remaining life of the equipment.

This is expressed as the number of inspections of whatever effectiveness has been performed in the past, assuming that this is the preferred inspection type for this plant.

The number of inspections can easily be converted to an equivalent number of inspections of a different effectiveness, based on the following relationships:

One highly effective is equivalent to two usually effective, is equivalent to four fairly effective.

If CUI is applicable in addition to internal thinning, the target damage factor is set to 5 for each mechanism so that the combined mechanisms will not lead to a damage factor greater than 10.

4.1 Method4.1 Method4.1 Method4.1 MethodThinning Mechanisms:Thinning Mechanisms:Thinning Mechanisms:Thinning Mechanisms:

Determine the current technical module subfactor. If this is less than 10, then use the SCC module escalation factor (years since last inspection) of 1.1 to determine the number of years until a TMSF of 10 will be reached.

As a default, perform a Fairly effective inspection at that time as a check on the SCC condition.

If the current TMSF is greater than 10, use the relationships in Table 9-15 to determine the inspection level required.

It is recommended that the inspection be performed within three years of the last inspection, or as soon as practical if more than three years has elapsed.

4.2 Method4.2 Method4.2 Method4.2 MethodStress Corrosion Cracking:Stress Corrosion Cracking:Stress Corrosion Cracking:Stress Corrosion Cracking:

Current SCC TMSF Inspection Level Recommended

10 < TMSF < = 100 Perform Fairly Effective Inspection

100 < TMSF < = 1000 Perform Usually Effective Inspection

1000 < TMSF Perform Highly Effective Inspection

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4.3 Method4.3 Method4.3 Method4.3 MethodFurnaces Inspection Planning:Furnaces Inspection Planning:Furnaces Inspection Planning:Furnaces Inspection Planning:

Part 1. Long Term Damage:

If the current TMSF is less than 10, increment ti (operating

hours) by 10,000 (~1 year) until a TMSF of 10 is reached.

The number of increments is the time to the next inspection,

Tinsp. Use Table 9-16 to determine inspection requirements:

If the current TMSF is greater than 10, use the following

relationships to determine the inspection level required:

It is recommended that the inspection be performed within

three years of the last inspection, or as soon as practical if

more than three years has elapsed.

Part 2. Short Term Damage:

For the short term damage TMSF, perform following action.

Furnace Inspection Intervals With a TMSF Less

Than TenTinsp Inspection Method Inspection Time

> = 20 years Fairly Effective

Usually Effective

Highly Effective

5 years

10 years

20 years

> = 10 years, < 20 Fairly EffectiveUsually Effective

Highly Effective

3 years

6 years

12 years

> = 5 years, < 10 Fairly EffectiveUsually Effective

Highly Effective

Not Allowed

3 years

6 years

< 5 years Fairly EffectiveUsually Effective

Highly Effective

Not Allowed

Not Allowed

T insp

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Furnace Inspection Intervals With a TMSF

Greater Than Ten

Current SCC TMSF Inspection Level Recommended

10 < TMSF < = 50 Perform Usually Effective Inspection

50 < TMSF < = 500 Perform Highly Effective Inspection

500 < TMSF Perform Highly Effective Inspection plus perform Remaining Life Evaluation

Actions Required for a Short-Term TMSF

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4.4 Method4.4 Method4.4 Method4.4 MethodHigh Temperature Hydrogen High Temperature Hydrogen High Temperature Hydrogen High Temperature Hydrogen

Attack:Attack:Attack:Attack: