(Digital Presentation) Life Cycle Cost and Technical Analysis of Corrosion Control Methods to Prevent Failures in Water Service Systems

Abstract

INTRODUCTION Water service systems, such as drinking/potable water and process water (e.g., cooling water), are undoubtedly strategic in any industrial installation. Their continuous, reliable and quality-controlled operation must be therefore guaranteed. The stable operation of a water supply system (and of other processes/areas) depends on many factors, namely: preventive maintenance, operation within the range of specific conditions and appropriate design, among others. In a petrochemical estate, especially in the Caribbean where all-year-round exposure to harsh environmental conditions aggressively enhances corrosion, high corrosion-related remediation costs are incurred if appropriate corrosion protection/minimization methods, such as corrosion control by materials selection and/or intervention corrosion control techniques, were not implemented during the design and construction phases and/or are not currently in place, respectively. The focus of this study is to perform a combined life cycle cost and technical aspects analysis in order to evaluate the feasibility of several corrosion prevention techniques for two important and strategic pieces of plant equipment: a potable water tank and a direct cooling water (DCW) pipeline, in use at several companies at a petrochemical estate located in the Caribbean. At least five (5) different construction materials for both pieces of equipment under study were selected for the analysis. Cost estimates from different sources (vendors, suppliers, providers) were obtained. All costs were discounted by applying an appropriate discount rate. For convenience and to facilitate the comparison in the cost analyses, normalization of all costs to those of the (total) initial costs of the two pieces of equipment to be evaluated was done. An adequate service life of 30 years was selected for this study. METHODOLOGY Corrosion prevention methods: materials selection - Potable water tank Five (05) different materials, some combined with different coatings and other corrosion protection techniques, are considered as replacements: Stainless Steel 304 grade tank (SS 304 Tank), Hot Dipped (Zinc) Galvanized Steel Tank (HDG STank), Chlorinated Rubber coated Steel Tank with Cathodic Protection (CRC STank CP:), Polyurethane coated Steel Tank with Cathodic Protection (PUC STank CP), and (inorganic)Zinc Silicate coated Steel Tank with Cathodic Protection (ZnSC STank CP). - Direct cooling water (DCW) pipeline Five (5) different alternatives(materials) are considered as DCW pipeline replacements, in addition to a new (inorganic)Zn-silicate coated steel pipeline (ZnSC SPipe): Polyvinyl Chloride pipeline (PVC Pipe), Ductile Iron Pipeline (DuctI Pipe), Hot Dipped (Zn) Galvanized Steel Pipeline (HDG SPipe), Fusion Bonded Epoxy coated Steel Pipeline (FBEC SPipe), and 3-Layer Polyethylene coated Steel Pipeline (3LPEC SPipe). Life Cycle Cost Analysis (LCCA) The LCCA was carried out in accordance with the appropriate ASTM standard [1]. A reasonable 30-years life cycle was taken into consideration, as in other studies [2]. After calculating costs and in order to standardize and facilitate the comparison among the different techniques under study, all the LCC results were normalized to the (total) initial costs of purchasing (new) current equipment, (potable water) mild steel tank and (DCW) Zn-silicate coated steel pipelines. CONCLUSIONS A combined life cycle cost(LCC) and technical feasibility analysis of several corrosion control methods to prevent failures in water service systems at a petrochemical complex was carried out. A potable water tank and a direct cooling water (DCW) pipeline were the equipment chosen in the study. For the potable water tank, using SS304 as the material of construction was proven to be the best option(Figure 1) to replace the current (mild) steel tank. In the case of the DCW pipeline, keeping a currently installed zinc-silicate coated steel pipeline was a suitable choice. This study highlights the imperative nature of managing corrosion by selection of fabrication materials in plant equipment to minimize maintenance activities and to avoid failures associated with corrosion. REFERENCES [1] "Life-cycle cost analysis of corrosion protection systems is focus of new ASTM iron and steel product standard", Anti-Corrosion Methods and Materials, Vol. 58 No. 4 (2011)[2] D. Kowalski, B. Grzyl & A. Kristowski, The Cost Analysis of Corrosion Protection Solutions for Steel Components in Terms of the Object Life Cycle Cost. CEER 26 (3): 005-013 (2017) FIGURE CAPTIONS Fig. 1. Cumulative discounted & normalized LCC for potable water tank alternatives. The even slighter increment that Zn Silicate coated steel tank with cathodic protection (CP) alternative exhibits every 12 years is due to cost of replacing the zinc coating; while the CRC and PUC options present slight increments (not noticeable) every 3 and 4 years, respectively, due to the need of their respective coating´s replacement. Also, every 20 years the CP for the ZnSC, PUC and CRC STanks is replaced (not noticeable in their respective lines). Figure 1