The Equipment Design Process
335
a standard method for economic appraisals of materials alternatives. This method takes into consideration the various costs and
evaluates them in light of the time value of money and the effects
of taxes and similar events. It should be used as a checklist to
ensure that all relevant factors are considered.
g. Final selection. With the information from the above analysis, it is
now possible to make a materials selection with confidence that
the relevant factors have been considered. Often it is desirable to
select a second or even a third alternative material so that quick
adjustments can be made in the case of material shortages.
11.3 Controlling Corrosion by Design
It is impossible to completely eliminate corrosion, but it is possible to control
the corrosion rate and thereby keep it within tolerable limits, as discussed in
previous chapters.
Severe destruction of plant material can result when improper materials
are selected for a particular environment. Inspection and early corrective
action can result in major savings to plants and their facilities.
Consideration must be given to the design after facilities are placed in
operation. Operating personnel should monitor the condition of the piping
and equipment by nondestructive testing after an operating period. If these
on-stream and off-stream inspections indicate a potentially unsatisfactory
lifetime or a threat to the integrity of the equipment and plant, determining
the corrosion mechanism can be a guide to the solution. Rating tables for the
various metals and alloys, plastic materials, elastomers, coatings, or linings
can lead to improved performance.
In Chapter 3 the various forms of corrosion were discussed, which frequently can be prevented and or controlled by proper material selection
and/or appropriate design practices, and if specific in-plant procedures are
followed. For example, in the design of tankage, it is possible to eliminate
crevice corrosion by proper design. The use of butt welds is preferable to lap
welds. In addition, the use of butt welds is especially suitable for tank lining
applications. If lap welds are used, the laps should be filled with fillet welding or a suitable caulking compound to prevent crevice corrosion.
11.3.1 Protection from atmospheric Corrosion
When proper decisions are made at the design stage, many corrosion problems can be reduced or eliminated. It is better to reduce the possibilities of
corrosion in the beginning than to take elaborate steps later for the prevention of corrosion. A design engineer is not necessarily a corrosion engineer
335
a standard method for economic appraisals of materials alternatives. This method takes into consideration the various costs and
evaluates them in light of the time value of money and the effects
of taxes and similar events. It should be used as a checklist to
ensure that all relevant factors are considered.
g. Final selection. With the information from the above analysis, it is
now possible to make a materials selection with confidence that
the relevant factors have been considered. Often it is desirable to
select a second or even a third alternative material so that quick
adjustments can be made in the case of material shortages.
11.3 Controlling Corrosion by Design
It is impossible to completely eliminate corrosion, but it is possible to control
the corrosion rate and thereby keep it within tolerable limits, as discussed in
previous chapters.
Severe destruction of plant material can result when improper materials
are selected for a particular environment. Inspection and early corrective
action can result in major savings to plants and their facilities.
Consideration must be given to the design after facilities are placed in
operation. Operating personnel should monitor the condition of the piping
and equipment by nondestructive testing after an operating period. If these
on-stream and off-stream inspections indicate a potentially unsatisfactory
lifetime or a threat to the integrity of the equipment and plant, determining
the corrosion mechanism can be a guide to the solution. Rating tables for the
various metals and alloys, plastic materials, elastomers, coatings, or linings
can lead to improved performance.
In Chapter 3 the various forms of corrosion were discussed, which frequently can be prevented and or controlled by proper material selection
and/or appropriate design practices, and if specific in-plant procedures are
followed. For example, in the design of tankage, it is possible to eliminate
crevice corrosion by proper design. The use of butt welds is preferable to lap
welds. In addition, the use of butt welds is especially suitable for tank lining
applications. If lap welds are used, the laps should be filled with fillet welding or a suitable caulking compound to prevent crevice corrosion.
11.3.1 Protection from atmospheric Corrosion
When proper decisions are made at the design stage, many corrosion problems can be reduced or eliminated. It is better to reduce the possibilities of
corrosion in the beginning than to take elaborate steps later for the prevention of corrosion. A design engineer is not necessarily a corrosion engineer