Contrastación de hipótesis Hipótesis general

There are various ways of contracting for construction and design management. An EPC or design build contract is the joining of the engineering design, procurement, and construc-tion management funcconstruc-tions with one supplier. Owners can elect to hire firms with the in-house expertise to manage all three functions or a design firm and a construction manage-ment firm who have joined forces to provide these services under one contract umbrella. The advantage of the single con-tract is the single point of responsibility between the owner and the supplier.

Some owners will elect to have separate contracts with the design firm and with the construction management firm, with the construction firm responsible for the majority of the procurement. The advantage of separate contracts is that the owner retains control over the design, and the design work can start before the construction management firm is selected.

When selecting a firm to manage the design and=or con-struction of the project, there are a number of strategy and planning tools that these firms must use to effectively manage the overall process. During the various phases of the project, cost estimates and project schedules are prepared. These estimates and schedules are constantly refined as more details of the project are developed.

At the conceptual stage of a project, the cost estimate(s) developed are utilized for the project’s overall business strat-egy. The initial return on investment (ROI) calculations are based on these preliminary estimates. These estimates and schedules although based on limited data, usually not more

than 10% of the total engineering, are critical to achieving the project’s overall goals. The selection of the key firms to supply the design, construction management, and estimating ser-vices is a critical early project activity. The preparation of the project estimates is usually a collaboration between the outsourced vendors and contractors who are familiar with the construction and design market, and the API manufactur-ing (owner) who is more familiar with the chemistry or the process and the cost structure of the company.

As the design progresses the estimate is refined. The assumptions made during the conceptual estimates must be evaluated for changes. In the initial conceptual estimate, there were constructability assumptions used to prepare the estimate, such as labor availability, equipment and material deliveries, and the sequence and methodology of the construc-tion work. At each refinement, the level of uncertainty is reduced and therefore the level of contingency for unknowns is also reduced. The overall contingency required for a project is in direct relationship to the level of uncertainty or predict-ability of the final cost of the project. In the initial stages of the project (10%), a contingency of 25þ% is common. At the completion of the detailed design and with the process com-pleted, the contingency should not be required at greater than 10%. In a complex process, an additional contingency is estab-lished for the final start-up and validation activities. The level of risk, which drives this contingency, is based on the com-plexity of the process.

When a project is ‘‘schedule driven,’’ it is imperative that a schedule be established early in the project and be utilized during the project. During the project planning, the schedule will grow in complexity and task breakdown as the overall project is developed. The schedule must be a working plan throughout the project. This plan will be updated as new data are known and to reflect the current approach to the overall project execution. An effective sche-dule must have relationships between the work items. The size and number of schedule activities on a project vary from project to project. Many computer programs exist that can arrange the schedule data in easy to analysis formats. A

pro-ject critical path method (CPM) schedule, to be effective, must have the necessary detail to show a clear critical path. The bar chart is the most common display of a project schedule (Fig. 8).

Figure 8 A typical bar chart.

A schedule can also be produced in an arrow diagram, which will graphically show all the activity prior to or depen-dent on an activity and subsequent activities, those, which follow an activity. This presentation can be very useful in the analysis of how a project can be executed. To monitor a project schedule effectively, the level of activity should be detailed to show the items that should be accomplished dur-ing a specific period of time to maintain the overall project completion schedule. The capabilities of the design and construction management firms or EPC firm to produce and monitor an effective project schedule in the complexity required to manage these projects is an important element in the selection process of those vendors.

The selection of the architectural=engineering (A=E) and construction=management (C=M) firms and the contracting strategy with those firms is a function of the schedule drivers.

Activities must be worked on concurrently to support the

schedule. The suppliers need to provide resources for project planning, early long lead procurement, and conceptual estimating. In many cases, the early involvement of these suppliers is contracted on a reimbursable or cost plus basis.

As the project becomes better designed and scoped, the con-tract between the owner and the A=E and C=M suppliers can become a guaranteed maximum price, lump sum or a reimbursable contract with schedule, and cost incentives. In planning the execution strategy, the resources for the start-up and validation must also be identified early in the process.

Many engineering firms have the in-house resources to plan and manage the start-up and validation activities. This is also important to decide when selecting the overall procurement strategy for the project.

With an effective, realistic cost estimate and CPM sche-dule in hand, the manager of a project can make effective decisions regarding the planning and execution strategy.

Many times marketing decisions will dictate the project com-pletion date, which could require additional funds to allow an acceleration of the project by either working overtime or add-ing additional shifts. When evaluatadd-ing the final schedule for an API project, the time required for the start-up and valida-tion of the facility is critical to the success of the project.

These activities usually start at the completion of construc-tion; however, their duration and requirements make it necessary to start these activities when phases of the construction are complete. Overlapping of these activities will also reduce the overall project schedule. The early planning and strategic development of an overall project strategy will identify schedule opportunities.

The sequence of the construction can then be planned to support the validation. The development of the validation strategy should be developed as part of the overall project execution planning. The strategy for contracting for the vali-dation services is a critical early activity. It is important to identify the process systems that affect or come in contact with the product. These systems must be validated. In a pro-cess if chilled water or steam is used to heat the jacket of a vessel but that steam or chilled water never comes in contact

with the final product, the utilities will not usually require validation. However, the instruments that control the steam to the vessel jacket will usually require validation. If the controls do not function properly then the product can be overheated or cooled. All pipe systems that transport product must be totally validated.

Another element critical to the completion of a project is the time required for testing of equipment and control systems.

In the project validation and procurement planning, all equip-ment, and systems, which require factory acceptance testing prior to shipment, should be identified. The specifications, and procurement documents should provide for the required testing and identify documentation of the testing procedure for the equipment and control systems prior to shipment to the site. In many cases, with skid-mounted equipment that often has microprocessor controllers, a significant amount of the IQ documentation and verification can be accomplished at the factory. This preplanning will save the overall project sche-dule. The testing, documentation, and validation activities are then accomplished in parallel with construction activities.

Equipment problems are flushed out at the factory prior to the installation in the field. This pretesting at the factory can increase the productivity of the construction installation and reduce the overall project schedule.

In the development of the process automation and con-trol system, the required testing of that concon-trol system and the factory-assembled components, and the process simula-tion program must be established with the general func-tional specifications. In an API facility, many of the control systems perform process functions that require strict validation. The functional description for the automation system should require a complete factory acceptance test (FAT). This test should simulate the entire process and pro-cess failures and alarms. The FAT should also check and verify that the control system cabinets and controllers oper-ate as designed. The factory acceptance testing of the pro-cess automation system prior to shipment and installation in the field is a critical step in the validation and start-up of the facility.