Page 320 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

298 CORROSION CONTROL AND PREVENTION

required. It should be borne in mind that sometimes process changes over time may
cause a problem leading to erosion–corrosion.

4.28.3 Construction Stage Checks
Inspection is of importance to ensure that fabricators are working according to design
codes and quality control. Assembled items are of the right material and specifications
for common items such as valves, piping, and welding electrodes must correspond to
the standard prescribed specifications. It may be necessary to perform trial runs with
the equipment supplied by manufacturers before full-scale operations.
The factors influencing plant and process design are as follows. This has to comply
with equipment and process data specifications with the following input:

1. Design philosophy, economic, and political considerations.
2. New materials and equipment design.
3. Data from similar or identical plant.
4. Materials data from manufacturers.
5. Established corrosion design data.
6. Data developed from corrosion testing.
7. Established corrosion design data.
8. Materials data from manufacturers.
9. Data from similar or identical plant.
10. Equipment and process data specifications.

Planned maintenance or regular replacement of plant equipment to avoid failure
by corrosion is an essential adjunct to design and constitutes the third phase of con-
trol. The factors contributing to a policy of planned maintenance philosophy are: (i)
predictable and reasonable rate of corrosion for material; (ii) discounted cash flow
advantage over life of plant in using a cheaper less-resistant material; (iii) factors
other than corrosion dictating regular maintenance; (iv) no feasible alternative to cor-
rodible material; (v) installed spare preferred policy for reliability of plant.
The design philosophy determines the emphasis placed on controlling corrosion
by this means, as opposed to spending resources at the construction stage to prevent
corrosion. Planned maintenance should be avoided when maintenance labor costs are
high or spares may be difficult to procure.
Planned maintenance consists of periodic shutdowns to inspect the equipment and
refurbish or replace equipment that failed because of corrosion or other failure mech-
anisms.
Regular maintenance of lower grade equipment is preferable over minimum main-
tenance of expensive or specialty equipment.
Periodic reviews are necessary to determine if the current corrosion control meth-
ods are adequate. Coatings on equipment may deteriorate and need to be replaced.
Inhibitor dosage has to be adjusted depending on environmental or process changes.