Chemical Technology February 2015

Big effect on small cause – Valve technology under stress Maintenance can be defined as the

degradation management of engineered materials (equipment and systems) to retain their performance within their designed operating parameters.

J ust as stress can accelerate deterioration of metals in a corrosive environment, operational stress moves equipment and systems toward failure. Limiting stresses within the operating environment maintains reliability. The elements of the maintenance which are relevant are: 1. Protecting components from stress 2. Monitoring their condition, and 3. Undertaking component(s) replacement prior to the failure threshold level caused by stress excesses. The impact of maintenance costs over time spans which can easily reach 25 years or more is finally much higher than savings made on the investment side when purchasing inappropriate valve technology, or when choosing solutions not being ‘state of the art’ technology. The aim of this article

The expectations for a production plant are evident: safety to the employees and the environment, constantly high product quality and plant as possible and operating and maintenance costs as low as feasible. Finally the dilemma often lies somewhere between aspects of CAPEX and OPEX. As an example, when using components with a low average material lifetime (AMLT), savings on the CAPEX side can be made, but, on the other hand, OPEX will be higher because they are replaced more frequently. On the other hand, attempts to reduce specific costs of maintenance or repair, most often end in higher CAPEX. Consequently, using high end components and ad- vanced technology will provide a safer operation of the plant, higher production quality and a more favourable total cost of operation (TCO). One to three percent of the investments costs of an indus- trial plant are caused by low and medium pressure valves, while maintenance costs including replacement and repair of such valves are estimated to be in the range of 4 – 7 % of the OPEX. Lifetime expectation of valves used in production pro- cesses generally is in the range of 5–10 years, depending on the quality of the valve, the working conditions, the frequency of operation and quality of maintenance. A standard quality valve is expected to provide ten years of trouble-free service in these applications. Speciality valves can give reliable service for time spans of 15 or more years. In extreme cases, valves only last about two weeks, and quite often valves have to be replaced after three to six months. In such cases it is mainly corrosion, abrasion and scaling that are the cause of these very short lifetimes. Themain effects are internal and external leaking, with all the consequent effects. When looking at butterfly valves, for example, various aspects affect the lifetime expectation (AMLT). One of the most important sources of valvemalfunctioning results from the design and quality of the sealing elements. The lifespan and reliability of elastomeric seated butterfly valves is largely dependent on the valve liner which is the heart of the valve. Careful evaluation of this seemingly simple element should

is to show, using the example of industrial (butterfly) valves, how quality of components is effectively influencing the cost efficiency of industrial production plants. Asageneralrulevalvescontribute1%–3 % of the total investment costs of industrial pro- duction plants. Therefore valves often suffer from a certain lack of consideration, even though, in the worst case scenario, one valve failing can lead to a plant shut-down. Hence it is important, from the beginning, to choose the most suitable flow control technology. This commences with the choice of the ad- equate valve type, and the definition of the

appropriate valvematerials to be used. Once the valves have been installed, and the plant put into service, operational and maintenance costs start running. Quality aspects of the valve have a considerable impact on operational cost, as, for instance, on pumping capacity, power demand of actuators, and energy efficiency of the entire plant. Corrosion is one of the major threads in industrial pro- cesses, having an important influence on cost aspects. Therefore it is important to design the valves by using innova- tivematerials and adapted solutions in order to prevent such corrosion damages and thus additional costs.

12

Chemical Technology • February 2015