By Nigel James
Control system migration projects go better with best practices. This is not a place you want to be flying by the seat of your pants. The following is a guideline for consistent and accurate planning and execution of control system migration projects. Adopting these practices will reduce project costs, shorten the project schedule, and reduce risk. These practices will also improve plant operation after the migration, particularly in the area of operator efficiency.
Selecting the New System
Once the decision is made that a new control system is needed, the next challenge is to determine the best one. The first rule of thumb is to not allow the selection process to become an emotional debate. Fortunately, there is a specific process that can reduce the subjectivity of the selection by prioritizing needed control system functions and features.
The first step is to build a list of selection criteria. These can range from vendor technical support to HMI features. The designated decision makers should then prioritize these criteria. Assign a weight or use a multiplier to determine prioritization. A matrix of these criteria with weighting factors should then be used to populate the vertical axis of a decision matrix. On the horizontal axis, the various control systems being considered should be listed.
An example is shown in Table 1. A weight of three indicates highest importance, while a weight of one indicates lowest importance. Each vendor is ranked against each criterion on a scale of one to three, with three indicating best performance and one indicating worst performance. Each criterion weight is then multiplied by each vendor’s ranking, and these subtotals are added to determine a total score with higher numbers indicating better performance.
Gathering information to rank each control system can be challenging. Corporate engineering groups, engineering firms or independent system integrators are a good choice for assimilating this information because many times facility end users do not have detailed technical information on a variety of vendors. The vendors themselves are not unbiased, and tend to only provide the upside of their products.
Once this data is gathered, populating the remainder of the matrix with scores is the next step. After this is completed, a quantitative score is achieved, and the highest quantitative scores represent the control systems that will best satisfy end-user priorities. While this process is subjective in terms of prioritization of criteria and applying rankings to control systems, it generally reduces debate, documents the decision-making process, and helps a facility or company determine priorities.
Front-End Project Definition
A requirement for successful migration projects is a thorough up-front engineering study to define the detailed work scope, and estimate the overall cost of migration. It’s not enough to take an educated guess at the requirements and costs of a migration project, hope for the best, and immediately move to the full engineering phase.
Migration projects are often much more complex than they appear at first glance. If done correctly, a Front-End Loading Study (FELS) should identify any potential difficulties with a migration project, and should provide plans to mitigate risks.
Why Migration Projects Fail
The granularity of the FELS will determine if additional deliverables are needed, and to what level the estimate and scope of work are detailed. The goal of this effort is not to complete detailed engineering, but to verify and quantify all primary functions on a project.
One of the reasons that migration projects often fail to address key components during the engineering phase is that these projects typically occur at 10-15 year intervals. Because they are not common projects, there is less knowledge of some of the hidden gotchas, making it imperative to use comprehensive migration checklists.
Engineering and system integration companies that have these checklists available are often a good resource for the engineering services needed for a migration project. Checklists provide for consistent design and improve overall quality. The checklists serve as information gathering tools to assist in developing a comprehensive scope definition for a migration project.
Detailed Cutover Planning
An effective detailed cutover plan addresses the following questions:
- What methodology is going to be used for cutting individual I/O over to the new system?
- In what sequence is I/O going to be cutover?
- What adjustments will operations need to make during the cutover?
- What staff is required for the cutover?
- What is required from a checkout standpoint to call a point migrated?
The cutover portion of a project is typically the most visible aspect of project execution. The decision to perform a hot cutover or use a window of outage time is always the primary decision that determines the details of the cutover plan. Regardless of plan is used, the cutover plan should at a minimum include: