June 27, 2011

Conceptual Design, FEED and Detailed Design Definition

I think the exact definition of the outcome of each design stage may vary, depending on company and industry, but here's a rough definition :

1. Conceptual Design (CD) 

Preliminary study performed to define:

  • Purpose of plant/project
  • Location of plant
  • Overall cost of plant (+/- 30%)

Design deliverables will typically include a design basis with main process parameters defined (=overall plant production requirements etc.), some overall block flow diagrams, a preliminary space study to define overall space requirements and finally an overall cost estimate.
The conceptual design is exactly what it says - a concept. You have a concept and flesh it out a little - maybe do some preliminary sizing calculations. This allows a rough cost estimate to be done (say, +- 30@50%), and the concept can then be compared with other concepts. At this stage, you may just have a process flowsheet.

An accepted definition of design is: the act of conceiving and planning the structure and parameter values of a system, device, process or even works of art. Normally, defining the scope (aka definition) of the project is a subject that the relevant authorities of a company must initiate.
Basic and detail design are separated by the important step of taking a decision (mainly by the board of directors, BOD) on whether to continue, expand, momentarily shelve, or altogether abandon a project.

The CD will be presented for the BOD who may decide to proceed with a Basic design.

The BOD may wish to consult with marketing and financial experts before reaching a decision. When discussing a multi-million dollar (preliminary) project they might have to consider the impact it will have on future company long-range policy and ask for a (present and future) market analysis for the products and raw materials. They may then decide to give it a temporary approval and ask for more basic work to be done as in a pilot plant. Or they may finally approve it. That's the moment FEED or detail engineering design starts. 

2. Basic design (BD) or (FEED)

Development of a well defined design package to in order to prove the feasibility and the cost estimate from the CD. Cost estimate may typically be refined to +/- 10%, and will be used as the final Go Ahead from the BOD.

Furthermore this is the start up package for Detailed Design (DD). In many cases this package may also be used as a tender package for a Design/Construction Contract.
Typical deliverables will include:

  • Process Flow Diagrams
  • P&ID's
  • Process simulations/calculations as required to complete the above.
  • Equipment Lists
  • Line Lists
  • Instrument lists
  • Site Plans
  • Plot Plan's (The overall layout approved - this is also required for)
  • Preliminary Equipment specifications (datasheets)

Other overall layouts which may impact process design (e.g. Hazardous area classification drawings, Fire zone layouts which may dictate shut down valve requirements etc.)

All of these drawings should preferably be finalised to status AFD (Approved For Design) which means that they are completed in all aspects except for what will be decided in the Detailed Design phase (vents/drains, vendor data etc.)When I say preferably, this is because depending on project/company strategy, it may well be decided to issue the BD package with a level of completion lower than AFD.

Basic design is about 50% process engineering, with about 50% of the process engineering effort being done there. Detail design involves much more work from the other disciplines. 

My summary is: Basic design goes up to process design: Flows, operating conditions, size of equipments, budget costematings, etc. Detailled Dsgn covers all details of piping and all works.

Basic engineering ,sometimes refered to as FEED, primarily provides preliminary estimates of the facility in other to give the EPCI (Detail engineering,procurement,construction and installation)contractor a basis for bidding. As a matter of fact, the basic engineering phase can entail evaluating the EPCI contractors. So there can be quite a few loose ends in the design at the end of the Basic which has to be knotted up at the Detailed engineering.

Basic engineering = basic study to allow everyone involved to agree on the exact scope of work to be done to solve the problem involved in the project and put a groos figure on how much it will cost , before going ahead with the detail engineering.

Usually, a FEED is required to establish the identity of the total capital costs required in a project – especially if it is to be “project financed” (the financed portion is paid by project generated revenue). Therefore, a FEED is simply an up-front, basic design that suffices only to identify the required resources within an accepted level of accuracy. In international project-financed projects, the lending institutions are the ones who set the level of accuracy required to evaluate a proposed loan. Inherently, then, a FEED is not sufficient to specifiy, purchase, install, startup, or operate a major process. The FEED is merely an outline with very basic engineering done. It is used to obtain the funds required to carry out the necessary basic engineering that will yield the final, detailed design that can subsequently be specified, purchased, installed, started up, and operated.

 Additionally, without detailed engineering done, a lot of project necessities were left unattended and major mistakes and omissions were made. Therefore, there may exist other interpretations or needs for a FEED through various parts of the world. There is no engineering God or Court that fixes how all engineers should interpret or employ engineering tools. Everyone is left to use his/her ingenuity and common sense in applying the natural laws and resources found world-wide.

The basis design is the same as FEED (front-end engineering design) as far as I'm concerned. You take the concept and do firmer calculations. This will be stuff like developing a mass & heat balance, putting together a proper P&ID (Piping & Instrumentation diagram), and doing things like equipment sizing (pumps, vessels, heat exchangers, columns etc.). At this stage you produce equipment specifications.

When you have the basid design done (process specifications, P&IDs, heat and mass balance, utility requirements etc.) this package (FEED package) then goes out to the other disciplines (such as piping, civil/structural, electrical, instruments). The main work of the process engineer in the design is now done. However, the disciplines will need to consult you to make sure in their 'detailed' design they actually capture the intent of what you wanted. They will keep coming back and asking questions like what should we do with this, or does it matter if we change this, or put this here. The detailed stage involves the discipline engineers looking at piping layouts, electrical distribution boxes and what not. Basically everything that is required to actually go and build a plant. That is the detailed engineering stage.

The process engineer in his/her basic design job determines the optimum diameter, the pipeline material of construction, corrosion problems, flow controls, flow regimes, operating conditions, alarms, pipe schedule, thermal insulation, instrumentation, traps, etc.
What are the parameters that guide him, economic, safety or environmental considerations, or what? He/she may need the help of a mechanical engineer to assess the costs of the as-finished work. So, the mechanical engineer's work doesn't just cover the detail design stage.

Having gathered the necessary information and made the relevant process flow sheets and techno-economic calculations, as the case may be, somebody has to decide on whether this preliminary job is sufficient to proceed or that it may require a further study.
Only upon this authority's decision the detail design engineering follows or not.

3. Detailed Design

All further design is developed until it reaches AFC status (Approved for Construction).
For process design (assuming the BD outcome was status AFD) remaining work will be limited to verifying that the actual piping layout, the equipment purchased etc is in line with the present process design and incorporate any updates required. Typically procurement of main equipment takes place during the detailed design stage and this requires interaction from the process engineer as well as other disciplines.

Detail engineering -on the other hand- may need the help of the process engineer, for example, in cases where a HAZOP review may be carried out. So, the process engineer is not only in charge of the basic design after all, her/his reponsibilities are spread over both stages, the basic and the detail design. Both stages may be coordinated by a project manager himself/herself answering to the job-commissioning authority.

Detail engineering = get the thing designed in detail by the relevant personel , so that you can put it into construction , installation , commissioning and handover to maintenance.
In addition to the above comes all the electrical/instrumentation/structural/building/ architectural works etc.

4. Construction
5. Installation
6. Commissioning
7. Start-up and Maintenance

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