The Basis of Design (BOD) document represents the client’s instructions to the design engineering organization about what is desired, and how the process design is to be done. The design basis also provides the who, the how, the why, and the when. This document summarizes the process engineering related activity for the given project – it describes the technical approach planned for the project. For large projects it is an extensive document. In certain cases, it includes HSE related information where a separate HSE design basis is not part of the engineering documentation. The Process Design Basis is a structured document and is developed sequentially for ease of understanding and guiding the process engineering team in developing other process engineering deliverables for the project.
Responsibility and Purpose of the Basis of Design
The BOD is prepared by the engineer or designer with inputs from all departments. For oil and gas projects, the basis of design is usually prepared by process engineers. The BOD is prepared during the pre-design stage, and it serves as the basis for all the design calculations and other design decisions. The basis of design for any project serves several important purposes like:
- It documents the major process and assumptions behind specific decisions.
- A BOD concisely captures the client’s requirements and vision into technical terms and design parameters.
- For the commissioning team, the BOD is an important document to evaluate the ability of a design.
- The BOD provides a listing of all major design decisions.
- It is a technical document providing the thought process of design professionals for developing the plant.
- A project basis of design helps in calculating the life cycle cost analysis.
Key Elements of a Basis of Design
A typical BOD pulls together information on a variety of project parameters. Each of these may have multiple subsections.
As seen above the BOD should cover:
Project background: This section includes a briefing of the project.
Project Objective: What should the project achieve? The objective should be clearly defined. For projects with multiple aims, this section should spell out the relative priority of each as well as methods for evaluating tradeoffs among them.
Document Purpose: This section lists the requirement of this document.
Project Scope: This section includes the overall scope of the project in details. In addition, the scope of each discipline involved in the project is briefed. For example, a typical oil and gas basis of design document may include the scopes or process team, piping team, pipeline team, civil team, control and automation team, electrical team, etc.
Input Data: What goes into the project? What information is required to deliver on the project? The required data should be clearly spelled out, so all parties are clear on what to provide.
Project Deliverables: What is the output of the project? All expected project documentation and engineering deliverable should be clearly stated as well.
Design basis: This section lists all the design information or assumptions for each discipline. Separate sub-modules of individual disciplines are prepared as process design basis, piping design basis, pipeline design basis, civil design basis, electrical design basis, C&A design basis, etc.
Constraints and Boundaries: What could limit the project? What constraints are imposed by the client, regulation, capital availability, schedule, or other factors? It is important to determine constraints at the start of the project and estimate their effect on the project.
Uncertainty: What is unknown or might vary? What risks require mitigation? How are the risks to be evaluated? Information should be given on what the uncertainties are and how to handle risk evaluation.
Design Criteria: In this section of the project design basis, various calculation bases are provided. For example:
- Sizing Criteria for pipes/pipelines
- Capacity determination for Partial Relief Valve
- Sizing Criteria for Partial Relief Valve Pit
- Sizing Criteria for Chemical Injection Skid
- Design Life
- Site environmental conditions
Codes and Standards: In this section, all the relevant codes and standards are listed along with their editions. Also, Government Laws and Regulations should be provided.
References and Appendices: This is the final section of the design basis. Here, all the references and appendices are attached to substantiate the above-mentioned decisions.
The above-mentioned points are not exhaustive. The content of a BOD will vary from project to project.
