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The Challenges in Integrating a Process Control System with Skid-based Equipment: A Case Study

by Robert Patrick

Most projects involve the same questions and challenges regarding the integration of the Process Control System (PCS) with skid-based equipment. This case study examines two approaches to Process Control Systems integration. In the first, the skid vendors were responsible for all aspects of the design, development, documentation, and factory testing of the control system with the system integrator handling only integration of the skid after delivery on-site. With the second approach, the system integrator was involved from the outset, taking the lead role in the design and development of the operator interface, data collection, and reporting while providing guidance to develop the control software.

This case study was a facility expansion, executed in two phases over a period of three years at a cost of $120 million. The project included equipment typical to biotech facilities such as utility skids for Pure Water (PW), Water for Injection (WFI), and Clean Steam, as well as process equipment such as buffer preparation tanks, bioreactors, clean-in-place (CIP) skids and lyophilizers. Phase A consisted mainly of the addition of utilities in one of the new areas of the facility, while Phase B included additional utilities and the process equipment. Both approaches need to consider the following items during the planning phase of a project:

  • What are the PCS requirements?
  • What equipment should be integrated with the PCS?
  • What are the responsibilities of the skid vendor versus the PCS systems integrator?
  • What hardware and software are acceptable (including revision information if possible)?

These questions should be addressed clearly in the User Requirements Specification (URS) for the PCS. The PCS URS should be provided to the skid vendors during the bidding process and agreed upon as part of the PO. The PCS requirements for this project included:

  • Uptime (redundancy)
  • Local control with view-anywhere capabilities
  • Data collection of Process Measurements, Alarms and Operator Events to a central database
  • Remote Notification of Alarms
  • Reporting (Batch, CIP, SIP) ad hoc
  • Consistent displays for ease of operator use
  • 21CFR Part 11 compliance as defined by the customer

The equipment in the facility was categorized into three different types based on the amount of required integration with the PCS.

With the Type A Equipment, the PCS was used to monitor and control all functions of the equipment. The PLC code was provided by the equipment manufacturer, while the PCS systems integrator provided the SCADA. Type A equipment included the PW, WFI, Clean Steam, CIP, and Bioreactor skids.

In the Type B Equipment, the PCS system provided no control or monitoring except for remote alarm notification. Type B equipment included operations such as the Glassware Washer, Autoclave, Depyrogenation Oven, and Lyophilizer.

For Type C Equipment, the equipment vendor did not provide any controls. The PCS system was used to monitor and control all parameters for the equipment with the PCS systems integrator developing all control specifications for these items. Type C equipment included utility storage and distribution systems, buffer preparation tanks, and solution preparation tanks.

During Phase A of this project, the skid vendors were responsible for the PLC programming, screen generation, documentation (SDS, FAT, SAT), and testing. The PCS systems integrator was then responsible for the integration of the skid after delivery on-site. In reviewing Phase A, the following issues were identified with this approach:

  • Inconsistencies of core modules, such as manual control of valves and pumps, led to differences in the operator interfaces. These inconsistencies caused operator confusion and increased training difficulties.
  • Skid vendors were forced to use unfamiliar SCADA software that increased the time required for development, and in some cases, required customer assistance to configure the software.
  • There were increased risks because some skid vendors were unfamiliar with best practices for development, making tag, screen, data collection and security conventions more difficult to implement.
  • Modifications that were required to achieve integration once the skid arrived on-site became an additional cost instead of being included in the initial development of the equipment's control system.
  • Some skid systems included their own data collection, database, and reports. For these systems, integration with the PCS was difficult and provided little customer benefit.
  • Inconsistency of document formats between vendors made the review process, test execution, and validation more difficult for the customer. The customer and validation contractor used the developed design and test documents to create validation documentation.

In an effort to improve the process, Phase B used a different approach. The skid vendors were responsible for the control programming, provided input for SDS documentation development and assisted during the FAT execution. The PCS systems integrator provided core PLC logic modules to the skid vendors and was also responsible for screen development, data collection, reports, documentation (SDS, FAT, SAT), and test execution. The advantages to this approach included:

  • Controls – By providing sample code for the skid vendors, the PCS systems integrator was able to use standard templates for core items such as auto/manual control of valves and pumps.
  • Design and development – The PCS systems integrator served as a second set of eyes with industry-wide experience to help design and develop the skids.
  • Screens – The PCS systems integrator was involved in the development of standard formats. These formats, which included screen layout, tag and screen naming conventions, security, and navigation, enhanced the effort to bring consistency throughout the facility.
  • Documentation – Consistent document formats were familiar and led to increased efficiency for customer review and testing.
  • Testing – The PCS systems integrator was involved during the FAT and therefore was able to identify issues or problems before the skid was shipped to the customer site. Improved integration and testing during SAT and commissioning also occurred because the PCS systems integrator was very familiar with the equipment and documentation before delivery on-site.
  • 21CFR Part 11 Compliance – With the systems integrator responsible for central data collection, security, and audit trails, a more uniform system was developed to meet customer requirements.
  • The systems integrator was also able to provide a second, local source of customer support for the skid controls.

From continuous involvement on both phases of the project, the system integrator provided core PLC modules, standard screen development, document templates and test execution that met the customer's needs for consistent displays, central data collection, and site-wide security. The following lessons were learned and recommendations emerged:

  • Specify upfront in the PCS URS the specific responsibilities for the PCS systems integrator and skid vendors so discrete roles remain defined to avoid overlap of responsibilities and cost overruns.
  • Involve the PCS systems integrator in the development of the skid software from the start of the project. It helps if this involvement includes having the PCS systems integrator present during the FAT.
  • Where applicable, specify standards for the skid vendors to follow so each vendor meets the same criteria and serves the customer's needs for a user-friendly, seamlessly integrated system.
  • Coordinate software development at the same level as the mechanical and electrical portions of the skid. Such coordination makes the integration process smoother and results in a more functional system when the project is complete.
  • Use the expertise of the PCS system integrator, who usually has a view of the bigger picture or the total facility and sustains a long-term relationship with the customer, to provide help with future needs and longer range planning.

Robert Patrick has been with Superior Controls in Seabrook, New Hampshire for over nine years, where he is employed as a Project Manager. He holds both a BS and MS in mechanical engineering and has 13 years of experience in the automation and controls industry, with an emphasis in biotechnology over the last seven years.

Page last updated: 5 March 2009