Table of Contents
- Purpose of Model Reviews
- Types of Model Reviews
- By Stage of Model Completion
- Reviewers
- Subjects
- References
1.Purpose of Model Reviews
Often model reviews are limited to checking for interference and consistency with key project documents such as P and ID’s.
While these types of reviews are obviously required and important, limiting the reviews to “design checks” does not take advantage of all the opportunities available for optimization.
The important thing to remember is that the model represents the plant that is to be built; the total end product in three dimensions. Therefore, to fully utilize this tool, all those personnel who may have an impact, and / or who will be affected by, or involved with the plant under design should and can contribute to the optimization of the design. The model is simply a convenient tool for this purpose.
Who are the people, other than the design team, who can contribute?
They include :
Construction personnel
Operators
Maintenance personnel
Safety and environmental personnel
Technical specialists
The construction personnel can provide input that can potentially reduce construction costs and / or improve the construction schedule.
The operating personnel must live with the plant once it is built. Their timely input can result in a design that is most logical for operator utilization by identifying operating concepts so that control rooms and key control stations are located on the same level, placing instruments and associated manual controls in logical proximity, allowing space for working storage, etc.
Often the operating personnel are presently, or have recently, operated similar types of plants and can, therefore, contribute based on practical experience.
Incorporating operator preferences, if they do not add to costs, can also improve startup and “commitment” by these key personnel. Conducting careful reviews with operating personnel can result in considerable savings during startup and mechanical completion, by minimizing the usual field modifications to valving, installing bypasses and changing instrument locations.
Meaningful reviews by maintenance personnel have a much more subtle and longer range impact. Maintenance costs, and often more importantly shutdown time for turnarounds, can be minimized if proper access, drop-out areas and monorails can be incorporated into the design. The method of handling equipment for maintenance can best be defined by the plant maintenance personnel based on their experience, proposed philosophy and available or planned mobile and rigging equipment.
Safety and environmental consideration are always important. The necessity of meeting ever increasing numbers of regulations must also be checked. The three dimensional model allows for quick checking of simple safety considerations such as identifying which pipelines should be provided with personnel protection, locating and directing the discharge of relief devices away from occupied areas, as well as determining patterns of egress.
The role of the technical specialist is based on his experience feedback from similar installations and often the owner’s specific requirements. Again this input may have a greater impact over the life of the project with fewer operating problems and longer service. The model review can also serve as a catalyst for an open exchange of ideas. In the preliminary stages, free wheeling discussions and sharp questioning and presumptions can lead to significant design optimizing with associated cost and / or operating savings.
The three dimensional model facilitates this sort of conceptual visualization and exchange of ideas. A sort of visual-verbal value analysis can be performed by “why” questioning and brainstorming around the model during the conceptual design stage.
Finally the model as a focal point of various design inputs (structural steel, piping, nozzle orientation on vessels, etc.) is a visual measure of design progress not unlike gauging construction progress by walking the site and seeing what has been erected.
2. Types of Model Reviews
The various types of model reviews can be segregated into three primary categories. These categories can be classified by stage of model completion, by the types of people reviewing or by the subject being reviewed. Within each of these categories of reviews there are several different types, which are described below.
3. By Stage of Model Completion
As the model progresses through its various stages towards completion, periodic reviews are held.
3.1 Preliminary Reviews
Preliminary reviews take place once the plant arrangement and equipment arrangement have been established. Various alternates may be shown as part of the review process. In this type of review, particular attention is paid to the plant layout with regard to access to equipment, bay spacing, flow of materials and personnel, open versus enclosed structures and other macro-considerations to establish construction and operating philosophy.
Agreement must be reached at this review prior to starting any detailed design. One of the most costly errors in an engineering construction project is to begin detailed design in an area where the equipment arrangement philosophy has not been adequately reviewed and agreed upon and is therefore subject to later changes. Preliminary reviews should be held as early as possible during the project but adequate time should be allowed for evaluating numerous alternates.
3.2 Intermediate Reviews
Intermediate reviews take the place when the final structural steel has been erected, final equipment has been fabricated and set and the majority of the major piping runs, duct-work, instrument and electrical trays have been installed. The primary purpose of these reviews is to review the routings to insure that process integrity has not been compromised, that the pipe, duct-work and tray runs are in accordance with the minimum cost criteria established for the project and to observe any potential interferences in the operability or maintainability, created by the routing of these items.
3.3 Final Reviews
Final reviews are held when the model has basically been completed. This occurs when all equipment, piping valves, instruments, electrical, structural and other items have been installed on the model. In this review, the items to be reviewed will include such things as the location and orientation of the valve hand wheels for operability, the location of local instruments for maintainability, piping insulation for personnel protection and other details.
Agreement on the location of all these critical items should precede the start of the piping isometrics design or the preparation of instrument location plan drawings, if required.
3.4 Consistency Checks
Once the final reviews have been completed and the revisions made, consistency checks are carried out immediately prior to photographing the model and shipment. Consistency checks insure that the model agrees with the design drawings which contain similar information.
While the primary check is made against the P and ID’s, other documents such as equipment arrangement drawings or steel platform drawings must be checked for conformance with the model.
Model reviews will vary in their approach and level of detail depending upon the function of the reviewer. Different reviewers will be looking for items that impact their areas of responsibility and, as such, will look at the model in different ways.
4.1 Construction Personnel
Members of the construction organization are primarily interested in the constructability of what is being designed. They must impact upon both the labor and material cost aspects of installing a particular design. They must contribute to the design sufficiently to insure that the plant will be efficiently and safely constructed.
In particular, construction personnel will be concerned with items such as available space for setting equipment into the structures, access to pipe racks with mobile equipment or the use of cable trays for wire as opposed to individual conduits.
4.2 Plant Operations and Maintenance Personnel
The plant people are primarily concerned with how easily the plant is to operate and maintain. Operations personnel will be looking for designs which minimize operator attention, which provide compact areas for their operators to concentrate their efforts on and ease of access to equipment.
The maintenance staff has a view point more closely aligned with the construction people. Since they will have to remove equipment set in place by construction, they will be looking for access aisles, space for movement of portable equipment, uncomplicated piping and instrument installations, platforms and the like. Maintenance personnel will also be concerned with how the design affects the reliability of the installations.
4.3 Specialists Groups
Various specialists groups will review the model for impact on their area of responsibility. Groups concerned with environmental, process safety and industrial hygiene aspects of the plant should impact on the design. Environmental personnel will be concerned about curbing and trenching to contain spills. Process safety personnel will review such things as the proximity of combustible materials to spark generating devices.
4.4 Engineering and Operating Management
Representatives from both engineering and operating management generally will review the model from a separate and distinct view point. Rather than involve themselves in the minute details of the design as shown on the model, these people will take on overview.
They will look at the model as a whole to insure that the design meets the general criteria established by their respective groups. Management will also review the model to insure that each group under their area of responsibility has contributed to the critique of the design.
4.5 System Technical and Design Engineers
This group maintains the primary responsibility for impacting on the design through model reviews. In addition to reviewing the model from the standpoint of process integrity, the system technical or design engineer must also consider all of the items covered by specialty groups discussed above. While it is not possible for this person to penetrate at the same level as the specialty group, it is important that he participate in all reviews and understand and coordinate required model revisions.
5. Subjects
Model reviews are held based on the subject matter to be covered. Specific examples of these types of reviews are shown below:
5.1 Process Integrity
A review for process integrity will focus on those items which affect the process performance and reliability.
Up around the plant in general and key equipment in particular.
Minimizing flat, horizontal surfaces, reducing the required number of equipment support legs, pouring of tapered concrete into the bottom of building columns, designing with enclosed, tubular supports rather than with angle iron are typical items that will be explored during a clean design review. While clean design is critical in food and pharmaceutical type plants it is significant in virtually all installations where dirt buildup will effect equipment operation and eventually process performance.
5.2 Cost Effectiveness
Cost effectiveness model reviews are held to insure that minimum cost practices are being carried out to the maximum extent within the constrains of the project. Examples of this are : reviewing the model to minimize the number of bends of changes in elevation made by piping, reviewing equipment layout to reduce the size of the building and reviewing cable tray runs to optimize routing.
Obviously, there are constraints to the minimum cost approach which may preclude cost is a constraint. However, these constraints should only be considered when deciding to make a change and should not be taken into account while trying to generate potential ideas for change.
5.3 Environmental
Environmental review will focus on the effects of the plant design on the environment. The model makes it easy to visualize the enclosed areas which must be vented and the areas around potential spills. These are the types items of that should be covered and resolved during an environmental review. This type of review should also cover the design of environmental protection equipment installations.
5.4 Safety
Safety reviews are extremely important and should be carried out in extreme detail. Review of mobile equipment traffic patterns, proximity of combustible materials to potential spark generators, proximity of toxic materials to the personnel, ladder and platform installations and “head knockers” are typical areas that should be examined during a safety review.
5.5 Constructability
The ease of constructing a facility is the prime concern during a constructability review. The ease of bringing large process equipment into structures, the erection sequence of structural steel, the advantages of running wires in trays as opposed to individual conduits are typical of those items covered in a constructability review. Of course, process integrity, cost and other factors are considered as part of the constructability critique.
5.6 Detailed Checklist
A detailed checklist ref. 6.1 exist which gives guidelines of subject to be covered during the model review.
Document
| Number | Title | Level |
| BN-DG-C6 | Checking of Piping Design Model and Definition of Percentage Completion | 4 |