Design for Corrosion Prevention

Expensive service failures caused by corrosion wouldnot occur if proper precautions were taken at thedesign stage. Moreover, mere random application ofpreventive corrosion control can be fallible. Design foreffective corrosion control requires comprehensive useof an integrated work system. This system relies on adesign team cooperating closely within an inclusivelogical framework in which ‘‘lateral thinking’’ canprove useful.

Such a team of experts is vital for the design ofreliable, safe, lasting, and effective structures andequipment. These experts should represent manage-ment, design and drafting, production and erection,research and testing, operation and, last but not least,quality control. The team’s combined creativity, con-trolled by the integrated design system, has a profoundeffect on the resulting cost, design and performance.Immediate tryout of ideas in sketches, computerevaluations and simulations, models, prototypes, andtesting enhances this effect.

The actual analytic work preceded by the gatheringof all relevant extra- and intramural information.Environmental conditions which affect the product instorage,production, transport, erection, andoperationare investigated. The team organizes working se-quences, procedures, work flow, and the division oftasks, and responsibilities are established. The teamweighs the economic implications of any prospectivehazards against those of the reciprocal safeguards.Hazards can stem from the corrosivity of media,corrosion damage, material weakening, malfunction,contamination, loss of usage or downtime, loss ofproduct, and collapse of utilities. The safeguards areachieved by using comprehensive records, analyses ofenvironments, research and testing, data systems forcorrosion management, economic appraisals, the con-cept of integrated corrosion control, planned design,productionqualityassurance,andstructuralreliability,and by attention to maintainability, nondestructivetesting programs and corrosion control feedback.

The selection of materials and design forms solelyon the basis of their function cannot provide safe andreliable structures or equipment. Corrosion can ruineven the best creation. The designer must delay or stopcorrosion by an integrated application of corrosioncontrol which gives tactical, logistic, and (most im-portant) logical support to the design entity.

Functional considerations encompass the evalu-ation of weights and performance, operational char-acteristics, manufacturing schedules, and unit cost.Integrated corrosion control deals with materialscompatibility, geometry, mechanics, surfaces, protec-tion, maintainability, and economics. Some of theseanalyses cross the boundary between corrosion controland functional design; jointly they result in thecorrosion control concept and the design plan. Figures

1–17 illustrate these concepts, contrasting functionaland integrated approaches to design.

1. Materials Selection

The materials are selected to suit the functionalrequirements, and be able to function safely for aneconomic period and at a reasonable cost. In abalanced design, the materials form a well coordinatedand integrated entity, correctly specified and conform-ing with specifications. Even high-quality materialscan become casualties as a result of poor design andindifferent corrosion control.

Requirements for the selection of materials are asfollows:

(i) All construction, preservation and associatedmaterials (including fasteners and weld materials)should be selected on the basis of their physicalcharacter, design limitations, fabrication character-istics, and optimum economy.

(ii)Designs should usematerially unified assemblies.(iii) More expensive materials than necessary should

not be specified unless required for prolonged econ-omy or preservation of personal safety and productquality.

(iv) When necessary, the mechanical advantages ofmaterials should be traded off against corrosionresistance.

(v) More corrosion-resistant materials should beused for critical parts and where high fabrication ormaintenance costs may arise.

(vi) Short lifetime materials should not be mixedwith long lifetime materials in nonrepairable sub-assemblies.

(vii) Materials which produce corrosive fumes innormal or exceptional circumstances should not beused.

(viii) When corrosion is expected, the thickness ofstructural materials should be increased, but over-design should not go past a reasonable limit; beyondthis limit, better materials should be used (Fig. 1).

2. Compatibility of Materials

In a design, the significant aggregate of structures andequipment reaches across material and unit bound-

Figure 1Functional and integration design approaches.

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