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22nd AFA Int’l. Fertilizers Technology Conference & Exhibition June 30th - July 2nd, 2009 Marrakech, Morocco

Optimization of Life Cycle Costs for High Pressure Valves through Intelligent Design Concepts for Critical Operating Sebastian Puls Product Manager Valves Uhde High Pressure Technologies GmbH

Germany

Optimization of Life Cycle Costs for a High Pressure Valve through intelligent Design Concepts for Critical Operating Conditions

Sebastian Puls UHDE High Pressure Technologies, Hagen, Germany

Uhde High Pressure Technologies designs and manufactures valves and piping for the Urea industry since 1960. Over the years Uhde HPT has co-operated with all major licensors and contractors in the industry, like Stamicarbon, Snamprogetti, Toyo, Urea Casale, Kawasaki Heavy Industries, Mitsubishi Heavy Industries, Chiyoda and Uhde GmbH. In these years Uhde HPT has gained vast experience on the various requirements stipulated by licensors and contractors as well as on the actual plant performance.

Copyright Š Sebastian Puls 2008

Sebastian Puls Introduction According to the interaction of pressure, temperature and aggressive media the high pressure part of the Urea process is the most critical section.

This leads to the fact that beside the reactors, the design and dimensioning of the control valves of the high-pressure-synthesis has a particular importance.

In the past 10 years the plant capacities have almost been doubled and according to the leading licensors this trend will continue in the future.

Industry is already considering capacities of 5000 mt/d and more.

This demand for higher capacities of the plants and tightened technical requirements lead to larger and more complex valves.

The valve manufacture has to identify the critical parameter and design the most suitable and cost optimized valve for the customer from the point of view of the life cycle costs for a valve.

This includes: • Design parameters and their influence on the lifetime of a valve.

• Corrosion • Knowledge of the critical parameter “Cavitation” • Implementation of counter measurements to extend the lifetime • Repairing and overhauling of valves • Stocking of spare parts The intention of this paper is to allow plant operators and contractors to look at the life cycle costs for a valve from the design till the decommissioning of the valves and to get a feeling for the criteria to be taken into account having the most suitable valve for the least possible life cycle costs.

Life Cycle Costs Life Cycle Costing also called Whole Life Costing is a technique to establish the total cost of ownership. It is a structured approach that addresses all the elements of this cost over its anticipated life time. The results of a Life Cycle Costs analysis can be used to assist management in the decision-making process including the choice of options. One of the best ways to reduce the life cycle costs for a valve is to increase the lifetime and maintenance free period of the valve.

The impact of the initial costs is usually by far overestimated.

The life-cycle cost of a valve can be calculated using the formula: Life Cycle Costs = C + Mpw + Epw + Rpw - Spw. Where the pw subscript indicates the present worth of each factor.

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The capital cost (C) of a project includes the initial capital expense for equipment, the system design, engineering, and installation. This cost is always

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Sebastian Puls considered as a single payment occurring in the initial year of the project, regardless of how the project is financed.

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Maintenance (M) is the sum of all yearly scheduled operation and maintenance (O&M) costs. Fuel or equipment replacement costs are not included.

O&M costs include such items as an operator's salary, inspections, insurance, property tax, and all scheduled maintenance.

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The energy cost (E) of a system is the sum of the yearly fuel cost. Energy cost is calculated separately from operation and maintenance costs, so that differential fuel inflation rates may be used.

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Replacement cost (R) is the sum of all repair and equipment replacement cost anticipated over the life of the system.

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The salvage value (S) of a system is its net worth in the final year of the lifecycle period. It is common practice to assign a salvage value of 20 percent of original cost for mechanical equipment that can be moved. This rate can be modified depending on other factors such as obsolescence and condition of equipment.

For the Life Cycle Cost of a valve especially the Maintenance expenses (M) and the extension of the lifetime for a valve have to be taken into consideration. The optimization of the Life Cycle Costs already starts during the design of the valve.

Design Parameter and there influence on the lifetime of a valve Among the running urea plants a lot of different operating conditions are utilized. This leads to a number of valve types (each valve has its own article-number and is unique) which has to be taken into consideration especially when talking about the supply of replacement valves. The picture below visualizes the different scenarios arising when designing a valve.

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(Picture 1:Possible scenarios for designing a valve)

Depending on the requested case: UHDE replacement, On/Off or control valve up to 60 criteria are necessary to design the valve which is shown in the picture below.

(Picture 2: Control valve datasheet)

Of certain importance to increase the lifetime of the valve and therefore to reduce the life cycle costs is the chosen material.

While defining the material for the valve body and for other internal parts that are in direct contact with the media, the operator should be aware of the different limits of corrosion rates. The obvious differences between the different types of materials are highlighted below.

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(Picture 3: Common Urea materials)

The table shows that the corrosion rate varies up to 350% depending on the used material and requested specification. A better corrosion resistance leads to a longer lifetime and therefore could reduce the life cycle costs.

Beside the above mentioned materials the material SAFUREX or other premium alloys also have a positive effect on the reduction of the life time costs through their good corrosion resistance.

Critical Parameter “Cavitation� for the design of valves The valve manufacturer has to take the threat of occurring cavitation, flashing or choked flow into consideration. To calculate cavitation and flashing, it is essential that the valve manufacturer is provided with the correct process and fluid parameters by the customer. For the calculation special developed software programs are used.

Major influence on the lifetime of a valve has the state of cavitation.

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Sebastian Puls (Picture 4: Cavitation diagram)

Cavitation occurs when the vapour pressure of the medium running through the valve is between the inlet pressure P1 in the upstream and the outlet pressure P2 in the downstream as shown in the picture 4 above.

The cavitation causes damages on the surface especially on the stem head and reduces the lifetime of the valve significantly in case no counter measurements are taken into consideration. This life time reduction has again an influence on the life cycle costs.

The technical solutions that are necessary to master the higher requirements will be introduced in the next chapter. The above picture visualizes the case of occurring cavitation.

Counter measures to extend the lifetime of valves Cavitation is one of the major criteria that reduce the lifetime of the valve enormously.

To prevent cavitation it is essential to implement an adjusted anti-cavitation cone which must be designed for each case. Such anti-cavitation cone increases the life time of the valve and therefore the maximum maintenance free time can be increased enormously since less down time increases the efficiency of the plant, the life cycle costs will be reduced.

Beside the anti-cavitation cone other measures like stelliting or hard fastening are possible to increase the maintenance free time and to reduce the life cycle costs.

Hard facing and stelliting does not avoid the cavitation like an anti-cavitation cone, but helps to increase the life time of the valve through a much stronger surface.

In case no counter measures will be taken into consideration the maintenance intensity, the down time and the expenses for spare parts will increase.

Repairing and Overhauling of valves The value of a valve can be more than a premium sports car and therefore the repairability is of certain importance. Repairing a valve is in many cases much cheaper than to procure a new valve. In the same context the lifetime of the valve increases and in this tenor reduces the life cycle costs for the valve. In order to minimize the down time of a plant it can also be a smart strategy, to have spare valves on stock, replace worn valves and overhaul the replaced valve until the next service period.

Therefore it is important to have a reliable valve manufacturer that also offers the ability to repair the valves. The ability to repair a valve can also be increased by intelligent designs such as the implementation of an exhalable seat or an exchangeable stuffing box body.

Stocking strategies of spare parts Beside the ability to repair a valve it is always recommended by the valve manufacturer to stock certain spare parts for start-up and for two years of operation. For the mayor parts the delivery time is not less than 2 months and the impact on the shut

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Sebastian Puls down time enormous. For the key valves it is therefore essential to have the main spare parts on stock. Special spare part recommendations by the valve manufacturer can help the plant operator to define the right parts and quantity.

The most common spare parts to be replaced during the lifetime of a valve are: o o o o o o

the packing the base/ground ring the valve stem the valve seat (if available) the stuffing box body actuator parts.

Especially the packing system is one of the critical points of the valve that should be replaced frequently during the use of the valve and when starting the process after a maintenance period.

Besides the stocking of spare parts, it might be recommended to stock a complete spare valve in order to secure the lowest shut-of time of the plant. This is mainly for the critical control valves the case.

This on one hand increases the initial capital costs (C) but enables the plant operator to act immediately and to reduce the shut-of time and in the same context increases the plant efficiency.

State of the art urea valves The product portfolio of UHDE High Pressure Technologies contains all relevant valves for the high pressure section of the urea process. The picture below shows an example for an angle valve.

(Picture 5: Angle valve DN 8�, PN 200)

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The shown angle valve has a diameter of 8inch, a pressure of 200 bars, a pneumatic actuator and is designed for a temperature of 200°C. UHDE`s angle valve portfolio contains the types on/off and regulating whereas the regulating valves are available with an exchangeable seat. The dimensions reach from 4–500 millimetres.

Beside angle type valves also a butterfly control valve is available shown in the picture below.

(Picture 7: butterfly valve, DN 8”, PN 180)

The shown butterfly valve has a diameter of 8inch, a pressure rating of 180 bars, a pneumatic actuator and a design temperature of 210°C. UHDE´s range of butterfly valves reaches up to a diameter of 12 inches.

The picture below shows an example for a check valve from UHDE`s product portfolio.

(Picture 6: check valve, DN 8”, PN 200)

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The shown check valve has a diameter of 8inch, a pressure rating of 200 bars and the valve is designed for a temperature of 205°C. Different types of cones are available and the dimensions reach from 4–500, too.

Beside this standard portfolio a lot of special designed valves are available on customer request.

Conclusion During the past thirty years the design criteria and multitude of varieties increased enormously so that the development of valves has become more complex. Due to the possible valve varieties the valve manufacturer has to pay special attention to all details in order to meet the customer requirements enabling the operator to optimize the life cycle costs of the valve. It should be taken into consideration that the initial costs for a valve do not always offer the best solution. The plant operator should be aware of the Life Cycle Costs and that he may be able to minimize the total costs of ownership through intelligent design solutions, spare parts and smart maintenance strategy.

Mastering the process of choosing the appropriate valve for each application for the most optimized Life Cycle Costs is a joint effort that can ideally be guided by the experienced valve manufacturer.

As explained other criteria like maintenance costs, spare parts or the chosen material may also have an influence on the overall life cycle costs are eventually the more expensive solution.

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