Risk-based Component Life Management in Fossil Power Plants a. Jovanovic,

RISK-BASED COMPONENT LIFE MANAGEMENT IN FOSSIL POWER PLANTS

A. Jovanovic, MPA Stuttgart, Germany

Dr. Aleksandar Jovanovic Head of Life Management Department MPA Stuttgart Over 20 years of experience in the area of applied research for power plants, working in manufacturing, operation and research internationally [email protected]

Abstract The paper provides review of current practices and trends in the area of risk-based inspection (RBI) and risk-based life management (RBLM), primarily by looking at the current European work. It highlights the background and needs of industry in the area of RBI/RBLM and indicates some current solutions and results yet to be achieved in the new European project RIMAP. The project is aimed at developing European guidelines in the area of risk-based inspection and maintenance. The paper also shows how the principles of RBLM are practically applied in a European power plant, including the implementation aspects in the “non-ideal situation” (lack of data, uncertainties, need to combine experts’ opinions with results of engineering analysis, etc.). It has been shown through an example that the risk-based approach to life management can help optimize the inspection and maintenance programs and simultaneously promote plant economy and safety. 1 Introduction The interest in risk and risk-based approaches in inspection, maintenance and management in power and process plants has undoubtfully increased in Europe and elsewhere. Technical risk has become economic, public relation and political issue. Risk is now a days also an economic category, “merchandise” in a way, having its price, its market(s), its traders… Who invests in risk mitigation or reduction, expects an economically measurable benefit too. This change of paradigm means in the practice that it is more important to know and manage the risk, than to reduce or eliminate it "by all means...”. This is also the starting point for considerations made here – to examine how this change in paradigms applies to life management of critical components in power and process plants, where possible failures of these components can appear as the main source of risk. The European views on these issues will be presented in more detail, those from European research project RIMAP in particular.

Risk-Based Life Management OMMI (Vol. 1, Issue 1) April 2002 -2-

2 RISK and the maintenance concepts

The conventional “classic” approaches to risk propose solutions requiring to:

• assess risk/cost (statically, i.e. for one given set of conditions) • establish the “distance” between the current level of risk/cost and the limit one, and • propose/introduce measures for risk/cost reduction.

In the case that the measures have been successful, the plant can be kept in operation for longer time. Much of the consideration in this classical approach is devoted actually only to the internal plant costs, e.g. those of maintenance. Therefore, the main issue appears to be to find the right balance between gain/profit obtained by risk-reduction measures (e.g. life extension, higher availability and similar), and cost of the risk reduction measures. In the conditions of the liberalized market, the above approach is not sufficient, because it does not take into account the fluctuation of market prices. Therefore, the new market-oriented approaches advocate on-line dynamic analysis of the price cost ratio.

Including risk considerations into the daily practice of maintenance was not a straightforward and easy process. In order to come to its current state, the practice has passed through a number of phases, which can, generally, be described as

• corrective (“repair upon failure”) maintenance • scheduled (“time-based”) maintenance and • condition-based maintenance, leading nowadays to concepts known as

reliability-centered maintenance, risk-aware maintenance and similar.

The latter includes the new concepts like condition-based maintenance, reliability-centered maintenance (RCM) and risk-aware maintenance, risk-based inspection (RBI), risk-based life management (RBLM) and others.

These risk-aware solutions mean that it is necessary to move away from the traditional (officially prescribed) and time based practices, and to adopt strategies based on the condition state of the component and related risk. Thus, the overall safety, reliability and economy of the plant can be improved and the resources optimally used by ensuring that inspection is focused onto the critical components. Two elements of risk have to be assessed separately: probability (likelihood) of occurrence and nature of consequences. To derive the probability, a detailed knowledge of the continuing degradation mechanisms, which can affect each item of equipment, is required. This must be based on a thorough evaluation of the component itself (“condition assessment”), its operating conditions and the process in the plant. Similarly, assessment of the consequence requires a full understanding of the mode of failure and its consequent effect.

One of the main goals of the current practice is to concentrate on critical components. A “critical” component in the sense of this work (and it is consistent with the position of e.g. API 580/581, Seveso II guidelines, IEC 61508 and similar documents) is a component “mostly contributing to the risk”, where risk, again, has to be understood as defined in this work, later on. This practically means, that the components that can lead to the extreme, but only hypothetically possible “critical situations” (e.g. disastrous accidents) are not necessarily the most “critical components”. As pointed out by Koppen1 (1998), in most of the plants only about 20% of the components contribute to the virtually the whole risk in a plant (~80% of the risk). Practically, it means that it is


generally enough to concentrate on the critical 10 or 20% of components in order to eliminate most of the risk, achieving, thus, two seemingly incompatible goals, namely:

• savings (inspections concentrate on say only 20% of components, scope of inspection can be drastically reduced on the remaining 80% of components) and

• increased reliability, safety and availability (as the risk-bearing components are now those on which the inspection concentrate, the probability of unexpected failure decreases).

This approach is often misunderstood by people working in the area of safety, who, correspondingly, tend to create their scales of criticality based primarily on the possible/imaginable consequences (e.g. those of the most severe possible accident). 3 European approach An inquiry into the goal to establish needs of European industry in the area of RBI/RBLM was performed by MPA Stuttgart during 1999 and in early 2000 within the framework of EPERC (European Pressure Equipment Research Council and PLAN – Plant Life Assessment Network). Furthermore, the inquiry has used direct contacts and interviews to establish this collection of case studies. For each interviewed company the following information has been collected:

• Regulatory basis: codes, norms, standards, guidelines • Corporate policies: acceptance and expectations • Practical implementation • Future: "under construction", planned, expected

In projects led by large companies like Shell or research and other organizations (e.g. KINT2 project led by TNO, or project leading to API 5813) the risk-based approach in inspections evolved from an "interesting alternative" into official company policies, sometimes even national policies. Although the idea of risk as an optimizing measure for in-service inspection was accepted in principle by many, the first real tangible results appeared only in late 1980s with appearance in the USA the concept of risk based in-service inspection resulting in first published documents in early 1990s (ASME4 1991). Further, the NRC carried out verification and validation exercises while in Europe, a Working Group on risk-based in-service inspection has been set up within the European Network on Inspection Qualification (ENIQ).

When compared to the situation in the USA, the situation in Europe, in the term of regulation of RBI, is characterized by the following features:

• Single European documents are usually comparable to corresponding US ones, some of them, e.g. PED 97/23 and/or Seveso II guideline, can even be considered as a “European advantage”, but the consistency among single European documents is generally lower that in the US documents.

• Generally, the overall “coverage” of RBI is better in the US set of documents. In European documentation significant gaps appear, some of the issues are often not tackled at all and often there is no “central document”, which would link the existing pieces and create a consistent and comprehensive “RBI system” like the one of , e.g. API 581.


• In terms of “general deregulation” Europe has still a way to go – US organizations like PVRC, ASME, API and similar are often capable to react in a more flexible and, often, more efficient way than their European counterparts .

Much of the RBI issue in the USA is “profit driven” and much of it in Europe is “regulation driven”.

Practically, an overall concept of RBI/RBLM had to be specified and the available methods, tools, codes, standards, etc. embedded into it, developing additional methods, tools, documents, etc. if and where needed. These are some of the main goals of the RIMAP project of the EU (Figure 1).

RIMAP

RTD Project Coordinator DNV Lead Partner DNV

RIMAP

Demonstration Project Coordinator DNV Lead Partner EnBW

RIMAP RTD

RIMAP Network Project Coordinator MPA Lead Partner MPA Operating agent: JRC Petten

2 years 1 year

4 years

Development of European RBI/RBLM Guidelines / Application Workbooks

Applications of European RBI / RBLM Guidelines / Application Workbooks

Dissemination of information and results of work on the European RBI / RBLM Guidelines / Application Workbooks

Figure 1: European R&D project RIMAP (www.mpa-lifetech.de/rimap)

4 Sample Application of the Approach The applications showing direct consequences of the application of RIMAP project outcome (e.g. the RIMAP procedure) are yet to come, e.g. in the RIMAP pilot power plant of EnBW in Heilbronn, Germany, but applications of the general approach preceding RIMAP, are available. So, for instance, the solution proposed by Jovanovic5, “risk – informed” life management (RBLM) foresees the following main elements:

• RBLM procedure


• Risk assessment methodology • Decision-making methodology:

(a multi-criteria decision making methodology) used for ranking of risks (criticalities!) and, hence, for determination of critical components and locations and for choosing the right life management alternative (e.g. run, inspect, replace…)

• The software tool (ALIAS): for implementation and practical application of the RBLM approach, combining the above elements and providing the necessary supporting elements like databases, analytical tools, etc.

The RBLM procedure has been modified in order to fit the requirements of RIMAP, in which the current basic (draft) representation is shown in Figure 2. Besides the procedure, RIMAP also foresees the “RIMAP framework”, Figure 3.

Figure 2: Basic representation of the current draft of RIMAP procedure


DEMO2

WP4 (Application)

WP2 (RIMAP Framework)

RIMAP Guideline D2.2

(covers RIMAP Framework)

Appendix of the Guideline, RIMAP Procedure, at different

levels/steps D2.1

RIMAP Application Workbooks

RIMAP Procedure Application Reports from RIMAP Demo Project

RIMAP Framework

RIMAP Procedure

RIMAP Workprocess

Chapter 9 Subchapter 7.6 from

WP3.1 (Proba-bility of Failure)

Figure 3: RIMAP Framework consisting of RIMAP Procedure and RIMAP Work Process, and the hierarchy of the documents being produced in RIMAP: From the Generic Guideline on RBIM to the RIMAP Application Reports A sample application in Finland was placed in the broader framework of improving current practice of plant life management, focused on condition-based risk assessment of boiler and piping components in a thermal power plant (Finland, emphasis on replica and strain inspections). A coal-fired power station with two blocks has been selected as the sample plant. The details of the overall project (1995-1998) are reported in the work of McNiven6 (2000). The risk-based approach has been introduced gradually and on two selected items (boiler and main steam line). Further data about RBLM aspects are given in the paper of Jovanovic, Auerkari, Brear7. The procedure has been implemented in the following way. Decision to do RBLM and the objectives were defined by operator in consultancy with subcontractors. The objectives were:

• to ensure operability until the target year • to agree on the necessary action and investment • to agree on the targets with the authorities.

The target systems were the boiler and the main steam line from headers to turbine inlet flanges. The plant and the systems (Figure 4) have been correspondingly modelled in ALIAS system.


Figure 4: Boiler components modeled in ALIAS The following data have been collected (in paper folders first):

• design and manufacturing documentation, QA acceptance docs – as available in the plant (limited amount available)

• operating history data in the form of (handwritten) temperature and pressure logs, and, after 1990 on paper rolls, including records on startups (hot/warm/cold/total) – no computerized data acquisition data were available, additional data have been taken by sampling

• maintenance history including primarily inspection results and repair/replacement records

Generally, data before 1990 were very scarce. Only a minor part of the collected data has been stored electronically and a subset of these in ALIAS: mainly the RBLM-related data from the boiler (economizer) and the main steam line data, including inspections. Altogether, data for over 400 components in the piping system and over 250 components in the boiler were collected and stored in ALIAS. Assessment of data included primarily assessment of completeness and uncertainties, for:

§ design/manufacturing data component geometry (dimensions), material properties (e.g.


conservative/optimistic strength values), influence of manufacturer’s heat treatment; data on these were insufficient in 1960’s

§ operational history exhaustion due to creep and fatigue was calculated deterministically and the uncertainty related to past and future operating history taken as a factor assessed by experts

§ maintenance history limited records before 1990’s were partly compensated by the amount of data (primarily strain measurements and replica results, over 800 stored in ALIAS) available after 1990; no significant repairs before 1990, some bends (mostly on one leg of the piping) have been replaced due to high strains (max. 6-8% over diameter

Uncertainties, leading to determination of PoF-values were derived either from the data (e.g. measured NDT data, Material data, Figure 5) or from the models (assessed uncertainties in model parameters yielding uncertainty in results – e.g. creep damage development, Figure 6). The calculation is performed for different damage methods for each scenario considered (Figure 7).

For the identification of possible hazards the following has been considered/done: § HAZOP analysis has been considered, but eventually not done (economic

reasons and lack of personnel/tools) § expert identification of possible damage mechanisms: in current mode of

operation primarily creep, also corrosion in the boiler part.

Note: A new concept of combined event – consequence tree “The Bow Tie Scenario” is currently considered in RIMAP (Figure 7). For assessment of probabilities two options have been considered:

§ the quantitative assessment (e.g. PSA-like) and § the qualitative (expert-based) one.

For the similar reasons as for HAZOP, the quantitative analysis has not been done. The qualitative analysis has been made by four experts, three from one plant and one from another plant. Evaluation sheets containing questions as those shown in Table 1 were given to all of them

The assessment of consequences has followed the very same principle as the above evaluation of probabilities. The consequences considered have included:

§ technical (engineering) consequences including e.g. pressure loss, steam releases/leaks; potentially catastrophic consequences due to failure of bends were evaluated qualitatively

§ financial consequences like repair/replacement cost and business loss

§ environmental and other consequences like possible fatalities, injury of personnel and loss of reputation.


Material 10CrMo 9 10 in ALIAS database

Uncertainty in material properties modeled on the base of test data: Here distribution of creep test results (time to rupture)

Figure 5: Taking uncertainties in material data (here test results in creep testing) as the basis for determination of PoF

Figure 6: Creep damage development, model based on statistical analysis of data, determining PoF on the basis of the reached damage level =1


Figure 7: Combined Event – Consequence tree, “Bow Tie” scenario, basic principle

Table 1: Excerpt from the risk factor evaluation sheets

Label Economizer (2NA01/02)

Ava

ilabi

lity

Pro

babi

lity

of

dam

age

Shu

tow

n tim

e

Ava

ilabi

ty o

f sp

are

part

s

Ser

ious

ness

of

dam

age

if it

happ

ens

Z001 Econ inlet header 1 4 2 2 3Z002 connecting tubes Eco 1:to 1 4 3 4.5 4Z003 Eco 1 and Eco 2 1 2 3 4.5 4Z004 Eco 1 and Eco 2 1 2 3 4.5 4Z005 Eco 1 and Eco 2 1 2 3 4.5 4Z006 branching pipes 1 2 3 3.5 4Z007 Eco back wall and roof tubes 1 3 2 5 4Z008 Eco back wall and roof tubes 1 3 2 5 4Z009 connecting tubes 1 4 3 5 4Z010 Front wall hanger tubes 1 4 3 3 3Z011 connecting tubes 1 4 3 5 4Z012 connecting tubes 1 4 3 5 4Z013 connecting tubes 1 4 3 5 4Z014 Hanger tubes of superheater and the roof 1 3 3 4.5 3


Risk assessment has been done using the ALIAS-RBLM module. Its main results are shown as a risk map (Figure 8). The components have been classified in five risk classes (negligible, low, medium, high or extreme risk).

attemperator 3

superheater 2 lower part

superheater 2 inlet header

connecting pipes

attemperator 2

triflux HP

Figure 8: Risk map for boiler components (as applied in ALIAS system)

Risk assessment results provide basis for identification of critical components (e.g. the attemperator 3). The user-defined link between the risk level and the level of inspection (Figure 9) produced the inspection plan directly. The inspection plan has been embedded into the normal (MS Project based) planning of overhaul and other regular maintenance actions. It has also been compared with previous inspection plans and re-discussed with experts. An excerpt from experts’ evaluation sheets used for the risk map in Figure 8 is shown in Table 1.

The inspections have broadly followed the above inspection plan. Approximately at 20 locations, additional inspections (replica, magnetic particle, deformation/displacement, wall thickness) were performed.

Life assessment and fitness for purpose analyses included:


• strain analysis according to the SP249 Generic Guideline 4, implemented in the corresponding ALIAS module

• analysis of replica results using the corresponding ALIAS module.

Figure 9: Link between risk and inspection level (attaching the action level to the level of risk)

The results of NDT and strain measurements at a steam mixer have been evaluated outside the ALIAS system. This particular component was found to be underdimensioned. Inappropriate original heat treatment leading to the observed high strains at some bends could not have been improved.

The final step of RBLM involved reporting of the analysis results to agree on overall plans. Improved insight into the state of the plant and into the rationale of risk-based plant maintenance and life management have been achieved. The most important outcome of the RBLM and corresponding maintenance actions, after the RBLM exercise, has been that recently there have been no unplanned incidents in this plant and no further RBLM consultant services have been necessary. With due credit to those responsible for plant maintenance, this is not a trivial achievement for a CHP plant originating from 1960’s and remaining in continuous operation (mission critical regional supply of district heating, industrial steam and electricity).


5 Conclusions

Creating a successful RBI/RBLM guideline leading to successful applications is not an easy task. Despite large past and current efforts in Europe, the final shape of standardized practice in the area of RBI/RBLM has not been fully achieved yet. Current projects like RIMAP (www.mpa-lifetech.de/rimap) and other activities of e.g. EPERC-TTF3 and PLAN8, involving at the European and world level a very significant number of interested parties (more than 40 in the case of RIMAP) promise to deliver the desired level of European RBI/RBLM consolidated practice in foreseeable future (two to three years). The application example from a Finnish power plant successfully demonstrates the applicability and application of RBLM procedure like the one currently being developed in RIMAP project.

Acknowledgments

The support of the European Commission to the project RIMAP (Contract GROWTH Project G1RD-CT-2001-03008 “RIMAP”) is gladly acknowledged and appreciated here. Furthermore, many of the results presented were obtained thanks to precious help of partners in RIMAP RTD/Demo project: Bureau Veritas, Corus, Det Norske Veritas DNV (Coordinator), DOW Benelux N.V., EnBW GmbH, Exxon Mobil, Hydro Agri Sluiskil, JRC, Mitsui-Babcock, MPA Stuttgart, Siemens AG, Solvay S.A., TNO, TÜV Süd and VTT, as well as those of RIMAP-TN project: MPA Stuttgart (Coordinator), AIB - Vincotte, Allianz, Bureau Veritas, Bay Zoltán Foundation, CorrOcean, ASA, Corus, Det Norske Veritas, EDF, EnBW Ingenieure GmbH, ERA Technology Ltd., Electricity Supply Board, Exxon Chemical Company, FORCE Institute, Geodeco, Hydro Agri Sluiskil, Health and Safety Executive, IEC Israel, ISQ, Joint Research Centre, Laborelec - Electrabel, Norwegian Marine Technology Research Institute, METALogic, MIT Management Intelligenter Technologien GmbH , Monition Ltd., Petrobras S/A Petroleo Brasileiro, Siemens AG (KWU), Solvay, Technologica Group c.V., TNO Industrial Technology, Total Fina Elf, TÜV Süddeutschland, TWI, University of Wales Swansea and VTT Technical Research Centre of Finland. The application example was made possible thanks to the collaboration contract involving FORTUM (ex-IVO), its power plant Naantali and VTT, all from Finland.

References

1 Koppen, G. (1998). Development of risk-based inspection. Proc. of the First Intl. Conf. on NDE Relationship to Structural Integrity for Nuclear and Pressurised Components, vol. II, 20-22 Oct. 1998, Amsterda, Bieth and Mojaret, Eds., Woodhead Publishing Ltd.

2 [KINT] (2000) Final report ‘Herbeoordelingsplannen gebaseerd op risico’ (january 2000) PMP/KINT project “Risk Based Inspection programming”, J. Heerings, C. Buis, J. van Steen, PMP Apeldoorn, The Netherlands


3 [API] (1998). API Publication 581, Base Resource Documentation - Risk-Based Inspection, First Edition, Order # No.: C58101, © 1995-1999, American Petroleum Institute

4 [ASME] (1991). Risk-based inspection - development of guidelines, volume 1, general document, CRTD-vol.20-1, ASME – American Society of Mechanical Engineers, New York

5 Jovanovic, A. (1999). Integrated approach to risk-aware life management of plant components, Keynote lecture, Transactions of the 15th International Conference on Structural Mechanics in Reactor Technology (SMiRT-15) Seoul, Korea, August 15-20, 1999, Volume I, Plenary Lectures, Ed. Sung Pil Chang, pp 93-116

6 McNiven, U. (2000). Systematics and methodology in boiler plant life and condition management. Doctoral dissertation at Helsinki University of Technology, Department of Materials Science and Rock Engineering, Espoo

7 Jovanovic, A. Auerkari, P. Brear, J. M., Lehtinen, O. (2001). Risk-related issues in life assessment of power plant components: inspection, monitoring, code-based analysis, Proceedings of the Baltica V Conference “Condition and Life Management for Power Plants”, Porvoo, Finland 2001, June 6-8, 2001, edited by S. Heitanen and P. Auerkari, VTT, pp 427-448

8 Jovanovic, A. (2001b). Current European effort to establish guidelines for risk-based life management for components in power and process plants: PLAN-Pais, EPERC-TTF3, RIMAP, presented at Baltica 5 Conference, Porvoo 2001

Documents

Risk-based Component Life Management in Fossil Power Plants a. Jovanovic,