12 ADD CONTINGENCY (SECTION 313)

The result of these steps is an onplot (battery limits) estimate only. Estimate any offplot requirements separately.

Example

For this Class 1 estimate of a conventional technology plant, the estimator selected a contingency of 37 percent, yielding a total onplot estimate of $13 M.

Cautions

Extrapolation. Do not extrapolate the curve beyond the plotted points

in Figure 203-2. The curve may flatten for low average equipment costs, resulting in installation factors probably not exceeding 9 or 10. Obviously, the factor cannot drop as low as 1.0 for higher-than- average equipment costs.

Complete Plants. As this method is based on actual costs for

complete new facilities with a mixture of equipment types, the factors shown in Figure 203-2 are most directly applicable to estimating similar plants.

You can, however, apply the method with a reasonable degree of accu- racy to individual equipment items (e.g., adding or deleting items for a proposed plant before it is built).

Alloy Equipment. The data for the curve came from normal refinery

and chemical process plants that have a limited amount of alloy equipment and piping. For plants with large amounts of alloy equip- ment and piping, the factored curve (equation) should still work—the average equipment cost being higher and the factor lower because the cost of most bulks (other than piping), labor, and indirects do not vary from those of a carbon steel plant. Since we have no data to verify this assumption, consider the factored method less accurate for a plant with extensive alloy materials.

Modifications. For modifications to existing plants, installation

factors may be higher or lower than for new plants. Generally, they are higher due to inefficient plant layout, dismantling, delays, work restrictions, shutdown work, and so on.

For rough estimates, apply the factored method and adjust the cost at step 9. Increase the labor cost to reflect poorer productivity due to con- gestion, work restrictions, etc. If, for example, you assume labor and related field indirect costs to be 34 per cent of the total (section 603) and anticipate 50 percent more labor hours, then increase the plant cost by 17 percent, as follows:

(0.34) x (1.50) + (1 - 0.34) = 1.17

Using the semi-detailed method covered in Section 205, estimate the direct and indirect costs (including productivity effects) for extra piping, electrical, and other bulk materials necessary because of inefficient location of the new equipment in the plant. Then estimate any dismantling costs, both permanent and temporary, for construction access.

Unusual Construction Features. Estimates for plants in a building or

with extensive vertical structures, jacketed or refractory-lined piping, sophisticated or redundant instrumentation, or concrete storage pits require larger installation factors than normal plants. Multiple-train plants have slightly smaller installation factors from savings through duplication. If storage tanks are included onplot, the installation factor is smaller than for a normal process plant.

Guidelines for Counting Equipment Items

The following counting rules were used to create Figure 203-2 so they should also be used when making an estimate. Fortunately, the results are not very sensitive to the equipment count. (A ten percent variation in equipment count changes the installation factor by only four percent.)

Do Count

Count the following items as one each:

Each reactor, column, or pressure vessel (even if stacked or with a common internal head). Be sure to count relief, fuel gas knockout, condensate flash, condensate receiver, blowdown, and steam separator drums.

Each heat exchanger or cooling tower. Each shell for shell-and-tube exchangers. Each bay for air-cooled exchangers.1

Each stack of double-pipe exchangers if there is more than one stack per service.

As one item, each set of external plate heat exchangers for one vessel or other equipment item.

Each bayonet-type exchanger.

Each furnace, boiler, in-line burner, or combustor. Each pump and each installed spare.

Each compressor and each installed spare, blower, fan, filter, mixer, agitator, venturi scrubber, cyclone, crusher, ball mill, belt or screw conveyor or feeder, weigh feeder, vibrating feeder or screen, bag house, large dust collector with fan, coke handling bucket crane, etc. Equipment used for batch operations, if permanently installed.2

Do Not Count

The following items are included in the equipment cost but not the count when deriving the average cost per piece of equipment:

Drivers (motors, steam or gas turbines, power recover turbines, diesel engines, etc.)

Items furnished as part of a package3

Items that can be considered an integral part of another item Bag house fans

Boiler and furnace fans, coils, steam and mud drums, stacks, preheaters, and stack gas treating equipment

Column, vessel and tank internals, heating coils, jackets, and floating roofs

Gas turbine inlet and exhaust facilities

Silencers and inlet air filters for blowers and compressors

1 _{A bay is generally limited to about 600 square feet of bare surface per tube row; e.g., for six tube rows, divide total bare}

surface by 3,600. If more than one service per bay, count each service.

2 _{For example, for delayed coker plants, count each hoist and each power swivel for coke drum drill stems and each}

unheading cart, cutting tool dolly and switch valve.

3 _{A “package” consists of two or more equipment items mounted on a skid or module, with substantial amounts of piping}

and other bulk materials already installed. At estimating time, it is not usually known whether a package will come on one or more skids; therefore, count a package as one item even if it comes on more than one skid. Note that some systems are

Lube oil, seal oil, turbine gland leak-off and jacket water facilities furnished with mechanical equipment

Noise enclosures.

Pulsation bottles for reciprocating pumps and compressors. Vibrators for solids storage bins, etc.

Cyclones inside a pressure vessel.

Hopper and screw feeders furnished as part of a ball mill. Mixers, agitators, or bayonet-type exchangers furnished with vessels, reactors, or contactors.

The following items are included in neither cost nor count but covered in the installation factor:

Concrete sumps or pits

Electrical transformers, switchgear, motor control centers, and associated buildings

Items not permanently installed1 Non-process mechanical equipment 2

Items that are essentially piping items, even though handled as engineered equipment3

Any instrument items

1 _{Examples are some catalyst loading hoppers, some carts and dollies, portable platform scales, warehouse spares,}

depreciable spare parts, portable spent catalyst handling equipment (pumps and dewatering classifiers), and other mobile equipment.

2 _{Examples are elevators for people, bridge cranes (or monorails with hoists) for maintenance or catalyst loading, hoists for}

lowering people into reactors, rail car pullers, emergency electric generators, oil mist generators, instrument purge lubricators, septic tank pumps, and non-process HVAC equipment.

3 _{Examples are flame arrestors, small filters and strainers, finned pipe coolers, magnetic separators, small venturi scrubbers,}

steam injection heaters, small steam separators, small bin vent dust collectors, solids sampling systems, in-line static mixers, spray nozzles, air diffusers, duct work, desuperheaters, sulfur seals, chutes for solids, loading arms and spouts, lift lines or pipes, pneumatic vibrators, air cannons (blasters) for solids bins, silencers for vents, eductors, ejectors, sample coolers, sample accumulators, and rotary, slide gate, needle gate, or duplex clam shell gate valves for solids.