long-term protection of sheet piling structures · sheet piles, pipe piles or combi-wall systems,...

Long-term protection of sheet piling structures

Report Life cycle cost analyses

Acotec

30 March 2012

Final report

9X2686

Humidur LCCA 9X2686/R0004/902750/Rott

Final report 30 March 2012

CONTENTS Page

1 INTRODUCTION 1 1.1 Asset management 1 1.2 Corrosion 1 1.3 Long-term protection 2 1.4 The study 3 1.5 Maintenance 4 1.6 Inspections 5

2 INSPECTION METHOD 8 2.1 Protection of sheet piling structures 8 2.2 Basic criteria 8 2.3 Preservation requirements 9

3 LCCA OUTCOMES 12 3.1 Traditional PU coating 12 3.2 Alternative 13 3.3 Corrosion allowance 14 3.4 Cathodic protection 15 3.5 Metallisation 16 3.6 Duplex system 17 3.7 Acotec Humidur 18

4 CONCLUSION 19 4.1 Systems 19 4.2 Total costs overview 20 4.3 Recommendations 20


Final report - 1 - 30 March 2012

1 INTRODUCTION

1.1 Asset management

The long-term management of our assets/property/investments, etc. is of great importance. Without careful management, their functioning, availability and sometimes even safety can be put at risk. Moreover, the useful life of assets may be (significantly) reduced and not attain that originally foreseen, with the resultant costs of maintenance and/or replacement increasing dramatically. Sheet piles, pipe piles and combi-wall systems, all in steel, are used for a range of different port structures. Steel sheet piling structures often form part of a port structure intended to create a physical separation between the land and sea for the harbour functions. Sheet piles are manufactured from hot-rolled steel and have 'jaws' to create a closed, sealed wall. They come in many different types and sizes. In addition to sheet piling, pipe piles, combi-wall and other systems are also used in the wet sector. This study focuses in particular on the LCCA for steel sheet piling structures and fittings.

1.2 Corrosion

Corrosion can be described as the undesirable chemical or electro-chemical deterioration of steel that usually manifests itself in rust products on the surface of structures. There is a distinction to be made between chemical corrosion and electro-chemical corrosion. Chemical or dry corrosion occurs when metals are affected by the pure action of specific elements or compounds (e.g. oxidation of metals at high temperature). Electro-chemical or wet corrosion arises due to the formation of an electrical circuit, in which water is an essential part. The electrical circuit often consists of two different metals where an electrolyte is in contact with the metals. Electro-chemical corrosion is the most commonly occurring form of corrosion and it is implicitly understood that this is what is meant when talking about corrosion. A distinction is also made between the following different types of corrosion:

- pitting corrosion; - galvanic corrosion; - biocorrosion; - corrosion caused by stray currents.

This report does not discuss the different types of corrosions in any further detail. There is a distinction to be made between the water and land side of the structure. On the water side, a further distinction can be made in the different zones, i.e. above water,

9X2686/R0004/902750/Rott Humidur LCCA

30 March 2012 - 2 - Final report

the splash zone, the tidal zone, the low water zone and the permanent immersion zone down to the bed. Depending on the environment, corrosion speeds may vary in the above zones. Sheet piles, pipe piles or combi-wall systems, all in steel, are used for a range of different port structures. We work in a range of different environments, e.g. fresh water, brackish water, salt water and under varying conditions, and this all impacts on the corrosion process and therefore the loss of material from the steel structure. Moreover, the effect of a combination of different corrosion processes also needs to be taken into consideration. The CUR 166 acts as a suitable guideline for this purpose. Untreated steel used in structures that are exposed to outdoor conditions will corrode. Examples include bridges, lock gates, load-bearing structures, sheet piling structures, pipelines, industrial systems, offshore, infrastructure and buildings. Protection and often preservative is applied to steel structures in order to manage corrosion.

1.3 Long-term protection

It is important to consider management and maintenance aspects right from the design stage as part of the process of deciding on the most effective way to bring about the long-term protection of steel structures, etc. Nowadays, the vast majority of designs for port structures, etc., also allows for management and maintenance costs, as well as construction costs. The use of SE and a life cycle cost analysis (LCCA) will further support the decision-making process, with the potential to achieve substantial savings in operating costs. The requirements with regards to service life and availability, the prevention of delays, disruption and other indirect costs can also be taken into account as part of the decision-making process. During the design phase, consideration will always be given to whether the objects/components suit the function envisaged and what maintenance is relevant for that object/component in terms of cost. The component costs include not only the maintenance work itself, but also the effects of the reduced availability of the object. Consideration is also given to combining maintenance activities for a number of objects/systems so as to maximise availability. Although life cycle cost analysis is very important during the design phase, it will be applied through all phases, i.e. design, build and maintenance. The big decisions are made at the design stage, but the analysis will be continually fine-tuned and improved in the light of experience during the build and maintenance phases.



1.4 The study

Carrying out a life cycle costs analysis (LCCA) allows the costs and savings to be identified for the structure over the entire life cycle. This allows the most effective combination of existing and new work, different systems, etc. to be achieved on the basis of both building and maintenance costs. Royal Haskoning is currently involved in the new build and renovation of quay walls, sheet piling, bridges, sluices, pumping stations, quaysides and piers. The LCC analysis forms the basis within a project for selecting the desired renovation strategy, solution, system etc. In addition to the initial investment, consideration is also given to the expected maintenance costs and even the costs of reduced operational availability. Nowadays, and particularly in these economic times, we apply LCC more and more frequently within our projects; no longer as a separate exercise, but as an intrinsic part of the design process. We have a software package that not only carries out the basic LCC calculation, but can also factor in the more complex forms of financing. To summarise the benefits of this approach:

major savings on demolition and investment costs; value of the existing structure is retained; substantiated decisions; faster implementation time; high PR value; lower impact on the environment.

In the approach outlined above we are seeking to give concrete shape to wishes and requirements surrounding sustainability and innovation. Not through additional investment, but through smarter design, by renovating and by taking a carefully considered approach to decision-making.



1.5 Maintenance

To maintain the sheet piling structures and fittings, a management and maintenance plan needs to be established. Further detail will be added to the management and maintenance plan depending on the importance, availability, function, risks, etc. Maintenance strategies: - Preventive maintenance

Usage-dependent maintenance Condition-dependent maintenance

- Corrective maintenance

Fault-dependent maintenance One of the above strategies will be specified depending on the various factors and properties of the components, such as inspectability/measurability, predictability of maintenance and consequences of structural failure. Potential management and maintenance actions include inspection, repair, replacement and measures to extend service life. Preventive and condition-dependent maintenance are preferable to corrective maintenance if the costs of corrective maintenance are higher than the costs of preventive maintenance and the consequences of failure are not acceptable. The decision-making process for choosing the strategy is mapped out in the flowchart below.



Flowchart for specifying the maintenance strategy

To ensure maximum availability of the sheet piling structures and fittings and to minimise maintenance costs as far as possible, a low-maintenance design that allows for inspection is chosen, in which durability considerations apply to all materials/components/systems used. Due to the requirements placed on availability of the structure by the client, it is virtually impossible to apply a fault-dependent maintenance strategy. For this reason, the proposal is to use a combination of condition-dependent maintenance and usage-dependent maintenance for structures and fittings. In the case of condition-dependent maintenance, maintenance activities are carried out on the basis of the current condition of the component.

1.6 Inspections

Information on the current condition of an object/component is obtained by various types of inspection, both for the superstructure and the structure under the water with all types of structures and installations.

Component

great

good

small

great

poor

Risk of loss of

function

Certainty of loss of

function

Measurability of

condition

Change design

small fault-dependent

usage-dependent

condition-dependent



With respect to the sheet piling structures and fittings, a distinction is made between the following three types of inspection:

- Baseline inspection - Functional inspections - Technical inspections

The baseline inspection is carried out immediately after delivery. The basis for the start of the maintenance period are the delivery/handover documents and the inspection reports they contain that are provided to the customer at the time the project is delivered. These delivery documents, including the list of outstanding issues, must be provided to the management and maintenance organisation. It goes without saying that the contractor is responsible for rectifying any shortcomings. It is important that all elements are thoroughly inspected and documented, as all subsequent inspections throughout the service life of the structure will be referenced to this “baseline measurement”. The functional inspection is a visual inspection to identify whether objects are functioning properly and are safe. Technical inspections will also be carried out to determine the durability of the structure in relation to the design life. These technical inspections are particularly important to determine the condition of the components as they form the basis for condition-dependent maintenance. Measurements and soundings also play an important role, alongside inspections. Measurements are important to monitor potential deformation, etc. and soundings to ensure that the bed depth is at the right level and to check that the protection of the underwater structures is intact. Over the course of time, more detailed inspections/focused inspections of components/structures will be needed in addition to technical inspections in order to identify/justify claims patterns and to find out more about the quality and remaining service life of the components/objects. All the frequencies proposed above can be adjusted if damage/non-conformities are found that need to be monitored more frequently with a view to preventing any (consequential) damage. Underwater inspections are usually carried out by divers. Alternatively, the underwater inspection can be carried out using a cofferdam structure specially designed for sheet piling structures. The cofferdam structure allows the entire sheet pile wall to be inspected over its entire height in stages. In addition, cleaning activities can be carried out in dry conditions and further investigations, such as thickness measurements and even concurrent repairs, can be carried out.



2 INSPECTION METHOD

2.1 Protection of sheet piling structures

To compare the investment and maintenance costs of potential solutions that use protection systems for sheet piling structures, an 'LCC calculation' was carried out. This study considered the following solutions:

- Traditional coating systems; - Durable coating systems; - Metallisation; - Duplex systems; - Design corrosion allowance; - Cathodic protection.

2.2 Basic criteria

The following assumptions used within the Ministry of Public Works were applied for the calculation. An annual interest rate increase of 2.5% was applied and 2% for the inflation correction. A sheet piling structure in steel was assumed with an expected service life of 100 years. In addition, the calculation for the LCC was based on the building and maintenance costs as shown in table 1. The costs of inspection were disregarded in this instance.



The construction costs in the example above were based on new build (prefab). The maintenance costs are the total costs incl. accessibility, protection, etc. The calculations were carried out using the parameters in table 1, and the following (provisional) assumptions on the basis of estimates and experience. For the sake of convenience, the maintenance costs per type were (provisionally) left the same for all systems. A 3-type maintenance classification system is used in which KO = minor (preventive) maintenance, and refers to touching up minor damage, MO = intermediate maintenance, and refers to applying a topcoat after carrying out minor maintenance and GO = major maintenance, where the assumption is that the system will be replaced. The maintenance requirements and frequency are evaluated for the above systems depending on durability. No further combinations were considered, such as solutions with coating and cathodic protection or solutions with corrosion allowance and cathodic protection, etc.

2.3 Preservation requirements

The choice of a sustainable solution for the coating system is based on the requirements set in NEN/ISO 12944-2 with respect to extremely corrosive maritime environments, cat. C5-M. The highest possible requirements from the NORSOK M 501- ISO 20340 can also be included. Wherever possible, this memorandum was informed by sustainable techniques and applies the Ministry of Public Works approved selection procedure.



Table 1: Construction costs and maintenance costs for the protection of sheet piling systems 1. Traditional system Construction costs CC= € 1,100,000 Inspections 5 Lv=25 Type of maintenance Number Maintenance frequency Costs Minor maintenance 8 Once every 7.5 years €160,000 Intermediate maintenance

Major maintenance 2 Once every 40 years €4,400,000 2. Alternative Construction costs CC= € 1,300,000 Inspections 10 Lv=50 Type of maintenance Number Maintenance frequency Costs Minor maintenance 5 Once every 15 years €160,000 Intermediate maintenance

Major maintenance 1 Once every 60 years €4,600,000 3. Corrosion allowance Construction costs CC= € 2,500,000 Inspections 10 Lv=100 Type of maintenance Number Maintenance frequency Costs Minor maintenance Intermediate maintenance

Major maintenance 4. Cathodic protection Construction costs CC= € 1,100,000 Inspections 10 Lv =25 Type of maintenance Number Maintenance frequency Costs Minor maintenance Intermediate maintenance

Major maintenance 3 Once every 25 years €1,100,000 5. Metallisation Construction costs CC= € 2,800,000 Inspections 15 Lv=100 Type of maintenance Number Maintenance frequency Costs Minor maintenance 2 Once every 40 years €160,000 Intermediate maintenance

Major maintenance



6. Duplex Construction costs CC= € 2,700,000 Inspections 10 Lv=75 Type of maintenance Number Maintenance frequency Costs Minor maintenance 3 Once every 25 years €160,000 Intermediate maintenance

Major maintenance 7. Acotec Construction costs CC= € 1,600,000 Inspections 15 Lv=90 Type of maintenance Number Maintenance frequency Costs Minor maintenance 2 Once every 40 years (2% A x 400/m2) €160,000 Intermediate maintenance

Major maintenance



3 LCCA OUTCOMES

3.1 Traditional PU coating

On the basis of this data and the assumptions referred to earlier, the average cost per year for system 1 for a sheet piling solution is € 114,267. This is shown in graph form in figure 1. Value is shown on the vertical axis and time along the horizontal axis. A start date of 1 January 2012 is assumed.

EgalisatierenteBoekwaarderenteAfschrijvingenOnderhoudskosten

Beschermen staalconstructie Damwand1. TraditioneelTotaal kosten

Jaarlijks gemiddelde: 114.267 €

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Source Translation Beschermen staalconstructie Damwand 1. Traditioneel

Protecting steel sheet piling structures 1. Conventional

Totaal kosten Total costs Egalisatierente Equalisation interest Boekwaarderente Book value interest Afschrijvingen Depreciation Onderhoudskosten Maintenance costs Jaarlijks gemiddelde Annual average Fig. 1: average cost per year for system 1



3.2 Alternative



Beschermen staalconstructie Damwand2. AlternatiefTotaal kosten


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15.000.000,00 €

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Source Translation Beschermen staalconstructie Damwand 2. Alternatief

Protecting steel sheet piling structures 2. Alternative

Totaal kosten Total costs Egalisatierente Equalisation interest Boekwaarderente Book value interest Afschrijvingen Depreciation Onderhoudskosten Maintenance costs Jaarlijks gemiddelde Annual average

Fig. 2: average cost per year for system 2



3.3 Corrosion allowance


EgalisatierenteBoekwaarderenteAfschrijvingen

Beschermen staalconstructie Damwand3. Corrosietoeslag

Totaal kosten


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120.000,00 €115.000,00 €110.000,00 €105.000,00 €100.000,00 €

95.000,00 €90.000,00 €85.000,00 €80.000,00 €75.000,00 €70.000,00 €65.000,00 €60.000,00 €55.000,00 €50.000,00 €45.000,00 €40.000,00 €35.000,00 €30.000,00 €25.000,00 €20.000,00 €15.000,00 €10.000,00 €

5.000,00 €

Source Translation Beschermen staalconstructie Damwand 3. Corrosietoeslag

Protecting steel sheet piling structures 3. Corrosion allowance

Totaal kosten Total costs Egalisatierente Equalisation interest Boekwaarderente Book value interest Afschrijvingen Depreciation Jaarlijks gemiddelde Annual average Fig. 3: average cost per year for system 3



3.4 Cathodic protection



Beschermen staalconstructie Damwand4. KB

Totaal kosten


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4.800.000,00 €4.600.000,00 €4.400.000,00 €4.200.000,00 €4.000.000,00 €3.800.000,00 €3.600.000,00 €3.400.000,00 €3.200.000,00 €3.000.000,00 €2.800.000,00 €2.600.000,00 €2.400.000,00 €2.200.000,00 €2.000.000,00 €1.800.000,00 €1.600.000,00 €1.400.000,00 €1.200.000,00 €1.000.000,00 €

800.000,00 €600.000,00 €400.000,00 €200.000,00 €

-,-- €

Source Translation Beschermen staalconstructie Damwand 4. KB

Protecting steel sheet piling structures 4. Cathodic protection




3.5 Metallisation



Beschermen staalconstructie Damwand5. MetalliserenTotaal kosten


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850.000,00 €

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Source Translation Beschermen staalconstructie Damwand 5. Metalliseren

Protecting steel sheet piling structures 5. Metallisation




3.6 Duplex system



Beschermen staalconstructie Damwand6. Duplex

Totaal kosten


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Source Translation Beschermen staalconstructie Damwand 6. Duplex

Protecting steel sheet piling structures 6. Duplex




3.7 Acotec Humidur



Beschermen staalconstructie Damwand7. Acotec

Totaal kosten


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800.000,00 €

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Source Translation Beschermen staalconstructie Damwand 7. Acotec

Protecting steel sheet piling structures 7. Acotec




4 CONCLUSION

This life cycle cost analysis demonstrates how important it is to weigh up the options carefully and to be in a position to make well-considered decisions.

4.1 Systems

1. The analysis shows that a simple coating system is a high-maintenance solution with associated high costs, and can therefore be said to be the least economic solution.

2. An alternative, more durable solution would reduce maintenance intensity and therefore cost.

3. The calculations for corrosion allowance assumed a corrosion rate of 0.1 mm/year. In a salty environment, the corrosion rate is/will be significantly higher and can even run to a rate of 0.5 mm/year. This demonstrates that a design corrosion allowance on its own will not suffice and the expected service life will not be attained. A coating will always have to be applied to the structure as an additional measure and/or a system with cathodic protection applied. Additional measures were not included in the calculation in this instance. Corrosion allowance is not a realistic option.

4. A system with only cathodic protections is not the most economic solution to attain the required service life, and will have to be replaced several times. Additional measures will have to be implemented according to the conditions. These were not included in the calculation in this instance.

5. Applying protection using only sprayed metal (TSA) is not the most economic solution. Moreover, the level of protection may be reduced by objects in the vicinity of the structure that are not protected to the same extent. If aesthetics play a role, visible areas may need an additional coat. This has not been included in the calculation.

6. Protection by means of a 'duplex system', where the structure is first spray-painted and then a coating system applied, was shown to be an effective solution, albeit not the most economical one. It has a sound anti-corrosive effect and meets any aesthetic requirements.

7. The most economic solution was shown to be a highly durable coating system. This solution does not require any additional measures. The maintenance requirement is virtually nil/minimal and is mainly necessitated by any mechanical damage. The system can be designed for virtually any expected service life that is required. The system can be applied prefabricated and is easy and quick to maintain during the maintenance period.

The direct (upkeep/maintenance) costs are included in the solutions considered. The indirect costs were not considered in this instance. In addition, the aesthetic aspects and the environmental effects were not considered further.



It was demonstrated that a durable coating system is sufficient to attain the required service life and also that no additional measures are required; the requirement for maintenance is minimal and regular monitoring combined with minor maintenance actions when needed are sufficient to keep the system in a good state of repair. System 7 was clearly shown to be the most economic solution, where the requirement is for durable protection over the life time of the structure. System 7 is the high quality Humidur coating system from Acotec.

4.2 Total costs overview

Table 2 shows an overview of the total costs for the various solutions. Table 2: Table showing all options

Table showing all options

Solution Annual average1 Conventional 114,267€ 2 Alternative 68,470€ 3 Corrosion allowance 32,335€ 4 Cathodic protection 47,369€ 5 Metallisation 39,266€ 6 Duplex 39,742€ 7 Acotec 23,745€

4.3 Recommendations

Where considerations of durability, the environment and aesthetics play a role as well as economic aspects, then the solution with system 7 is the best option. Moreover, this solution can be said to be virtually maintenance-free and will ensure a high degree of availability, less disruption and lower costs.

=o=o=o=

long-term protection of sheet piling structures · sheet piles, pipe piles or combi-wall systems,...

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