prdswhen to inspect? a simplified and smarter approach to ......same api rbi rp 581 methodology...

PRDs...When to Inspect? A Simplified and Smarter Approach to API 581

James G. Mekker

Equity Engineering Group

Staff Engineer

• API RP 581 PRD RBI Overview

• PRDWise Methodology

• Difficulties with Implementing PRD RBI

• PRDWise Solutions

• Case Study

• Questions and Answers

Presentation Outline

A PRD RBI analysis determines an inspection plan for PRDs based on a Risk Threshold or Target

Risk of failure for a PRD increases with time in service

Eventually, that risk level hits a risk target in which risk is no longer

acceptable and inspection is required.

API RP 581 PRD RBI Overview

Risk Target

PRD RBI considers two potential failures that can occurFailure to open (FTO)

• FTO risk considers the effects on personnel safety resulting from loss of containment

– Stuck closed or fails to open valves.

– Opens above set pressure

Leakage (LEAK)

• LEAK risk considers nuisance issues valves can cause

– Spurious/premature opening.

– Device stuck open.


FTO RISK critical factors PoF

– Inspection History

– Similar service failure history

– Overpressure scenario frequency

– Protected equipment damage state

CoF

– Process fluid and operating conditions

– Overpressure scenario potentials

– Financial downtime impact

* Uses same CoF modeler as used for fixed equipment


Risk POF COF

Each Risk needs to consider both the Probability of Failure (POF) and Consequence of Failure (COF)

LEAK RISK critical factors

PoF

– Operating close to set pressure

– Inspection history

– Similar service failure history

CoF

– Shutdown loss of production

– Maintenance repair costs


Risk POF COF

What is PRDWise?

• Can be considered as a Level 1 analysis

• PRDWise calculates inspection intervals using the

same API RBI RP 581 Methodology (Part 1, Section 7)

– Simplifies data input by making wise (conservative) assumptions

for complex data

– Removes time dependency from the fixed equipment

PRDWise Method

Implementing PRD RBI with the time dependency of the

protected equipment’s damage factor

– Known to cause issues with PRD inspection intervals

– High damage factors significantly decrease the PRD’s

inspection interval

– Changing damage factors (due to high damage

susceptibility or inspection activity) can significantly alter

inspection interval, and that makes planning for pop-

testing challenging

Difficulties with Implementing PRD RBI: Issue 1

EX:

– An equipment and PRD were both inspected in 2010

– Next RBI equipment inspection due = 2025

– RBI PRD inspection interval = 7.5 years (Next inspection 2017)

User assumes, given a good PRD inspection in 2017, the interval would

increase or stay the same

In actuality, due to the increase of equipment’s damage factor over time,

the next interval PRD inspection interval DECREASES to 3.5 years


Difficulties with Implementing PRD RBI: Issue 1R

isk

Time

Risk Target

PRD Interval 1 PRD Interval 2 PRD Interval 3

PRD Risk

Protected Equipment Risk

PRDWise allows user to assign a non-time dependent

damage factor to protected equipment

– This removes difficult to explain decreasing intervals

– Technique already available for PRD Equipment (API RBI

RP, Part 1: Table 7.10)

– User can base the equipment’s damage factor on

knowledge of severity of the damage state or criticality of

protected equipment

PRDWise Solution: Issue 1

Experienced user needs to determine overpressure and heat

potentials

– PRD sizing study temperature and pressure is based on

maximum required relieving flow

– RBI temperature and pressure is based on the max potential

if a valve fails to open.



Overpressure Severity

Examples

Severe Valves protecting fired heater, high heat source or PD pump. Valves protecting high pressure difference (OP > 3*MAWP)

ModerateValves protecting normal heat source, centrifugal pump. Valves protecting medium pressure difference(1.3*MAWP < OP < 3*MAWP)

Mild Valves protecting Fire case and/or solar thermal expansion onlyValves protecting limited pressure difference (OP < 1.3*MAWP)

Simplifies data input for overpressure potentials

• Requires only an Overpressure Potential Severity

• A lot of data is required for PRD RBI

– This requires additional resources and time

– Some data gathering requires advanced analysis to derive

reliable data


• Makes wise (conservative) decisions for many of the

input variables


PRD Mechanical Data

Keyword PRD RBI PRDWisePRD Type

PRD Orifice Area

Inlet Size

Soft Seat

Set Pressure

Back Pressure

Installation Date

RD Upstream

Discharge Location

Block Valve Admin Controls

Pulsing Service

Parallel PRD Area

Current Inspection Interval

Unit Turnaround Frequency

History Of Actuation

History Of Chatter

Operates Close To Set Pressure

Piping Vibration

FTO Fluid Class

FTO Weibull eta

FTO Weibull Beta

Leak Weibull Class

Leak Weibull eta

Leak Weibull Beta

Protected Component Data

Keyword PRD RBI PRDWise Keyword PRD RBI PRDWise

Protected Components Injury Cost

Design Information Production Cost

Component Type Active Damage Mechanisms

Component Start Date Estimated Internal Corrosion Rate

WJE Measured Internal Corrosion Rate

BM Material Estimated External Corrosion Rate

CM Material Measured External Corrosion Rate

Furnished Thickness Cracking Susceptibility

CA Thinning Type

Insulation Type Equipment Lining

Geometry Insulation Complexity

Inventory Group Insulation Condition

Operating Conditions Inspection History

Estimated Percent Liquid Volume Inspection Date

Management System Score Inspection Grading Effectiveness

External Environment Measured Thickness

Population Density Component Damage Severity

Demand Cases Data

Keyword PRD RBI PRDWise

Active Demand Cases

Upstream Overpressure Source

Upstream Overpressure Potential

Heat Source

Heat Source Temperature

Number Of Block Valves

Block Valve Usage Frequency

Control Valve Normal Failure Position

Event Frequency

Demand Rate Reduction Factor

Overall Overpressure Potential

Overpressure Potential Severity

Inspection History Data


Inspection History

Inspection Date

Inspection Effectiveness

Result

Leak Result

Overhauled

Risk Analysis Data


Leak Tolerated

Time To Discover Leak

Stuck Open Valve Tolerated

Environmental Cost

Unit Flare Recovery System

Fluid Cost

Cost To Repair PRD

Time To Repair PRD

Area Risk Target Activation

Area Risk Target

Financial Risk Target Activation

Financial Risk Target

PoFoD Target Activation

PoFoD Target

Probability Of Fatality Activation

Probability Of Fatality

Minimum Allowed Inspection Interval

Maximum Allowed Inspection Interval

Include Leak Risk

PRD Isolation Possible

• Case Study compared over 575 PRDs

• Comparison included 4 scenarios

– PRDWise Analysis

• Damage Factor = Severe & OP Potential = Severe (Most conservative)

• Damage Factor = Selected using Table 7.10 & OP Potential = Severe

• Damage Factor = Selected using Table 7.10 & OP Potential = User

Selected

– Fully Quantitative PRD RBI Analysis

Case Study

7.57.9

8.38.6

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

DF SevereOP Severe

DF Table 7.10OP Severe

DF Table 7.10OP User Selected

FullPRD RBI

Ave

rage

Insp

ecti

on

Inte

rval

(ye

ars)

Analysis Inspection Interval Comparison

PRDWise

PRDWise

4.0

5.0

5.9

6.6

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

DF SevereOP Severe

DF Table 7.10OP Severe

DF Table 7.10OP User Selected

FullPRD RBI

Ave

rage

Insp

ecti

on

Inte

rval

(ye

ars)

Analysis Inspection Interval Comparison Including only High Risk PRDs

With less data, PRDWise can produce conservative

inspection planning results

Full PRD compared to Most Conservative PRDWise Analysis

– Average 1.0 years increase

– Average 2.5 years increase for high risk valves

Full PRD compared to Most Advanced PRDWise Analysis

– Average 0.3 years increase

– Average 0.7 years increase for high risk valves

Case Study Results

PRDWise Pros

• More resource efficient

• Requires less data

• Simplifies inspection planning

with removal of time

dependent damage factor

Fully Quantitative PRD Pros

• More accurate

• Produces longer inspection

intervals

PRDWise Comparison

Questions?

Thank You

prdswhen to inspect? a simplified and smarter approach to ......same api rbi rp 581 methodology...

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