Above: Ensuring installations are qualified to seismic standards requires good communications
When addressing the seismic qualification of plants and equipment, one of the most common problems identified is installation deficiencies. This is not to say that the installers (contractors) are not doing a good job; they are just not always installing equipment exactly as per the design. Changes in the position of a bracket or bolt, or the orientation of a support, however small, can negate the design qualification status.
When consultants are performing a technical assessment of a design, they perform calculations and, in some cases, run Finite Element Analysis (FEA) models to ensure that the design meets the requirements set out by the client.
This numerical method is generally used to support the design, substantiation, or investigation of various structures, including buildings, plant and equipment.
These kinds of analyses provide a clearer understanding of the physical behaviour of a complex object and produce an optimal design, based on the predicted performance and behaviour of the design. It is a technique that is able to calculate the safety margin whilst accurately identifying any weakness within the design.
Once completed, these designs are then passed to the client and installer. It is at this stage where the communication triangle between consultants, clients and contractors can begin to breakdown.
Factors in communication breakdown
Knowledge at the installation phase of a project is essential and the communication workflow around this is critical to the success or failure of an installation. Why something has been designed in a certain way has to be communicated at every phase of the process – from source to manufacture through to installation.
Any small change being made by any one person at any phase of the process may not have a perceived impact, but ultimately can completely change the seismic response of an item or make surrounding equipment a costly interaction concern when it previously was not.
However, not all deficiencies emerge because of changes in design, manufacture or installation; some result from human error that can occur when communicating under the squeeze of a project timeline and supply chain pressures.
Experience has shown that contractors – new to the nuclear industry – are potentially qualified to complete “regular” installations but it is recommended that an independent third party is used to assess the technical expertise in the contracting team to ensure they have the proper experience to work in nuclear facilities. This can help to overcome issues of corners being cut and missteps taken.
Installation jobs must be executed correctly and need to meet the required standards. Again, this is where verification and certification by a third party organisation can ensure installation procedures and standards have been met. No installer or asset operator wants to incur the cost of delays and project downtime if problems are discovered at the start-up operational phase, which could have been overcome at an earlier phase and at far less cost.
The cost of poor communications
When the contractor’s installation team has not followed the design exactly or has cut corners, this generally comes to light during the interim or post-installation walkdown when the works are nearing completion and the commissioning phase has or is about to start.
During the post-installation walkdown, a seismic review team will be on-site to review the works from a seismic safety perspective. However, when items have not been correctly installed (or as per the design intent), problems occur, with significant cost and time implications.
Any incorrectly installed items may need to be moved or even replaced, and additional justifications and calculations may be required. In some cases, a further walkdown may be necessary to confirm that any required modifications or repairs that have been made do actually now satisfy the design intent. Certain deviations could also add significant costs due to fixing or addressing the problem and may even cause delays in commissioning.
Ask questions now to avoid problems later
It sounds obvious, but our advice to contractors working in the nuclear industry is to ask questions or raise technical queries (TQs) promptly. If contractors cannot precisely follow the design for any reason, they should contact the designer before completing the installation. This will save the client time and money and avoiding potentially embarrassing incidents.
Walkdowns on site, even at short notice, are able to use experienced seismic engineers to review projects as they are developing, enabling accurate evaluation of any issues before they become impactful problems, helping prevent the time and cost issues that could arise.
The key to the ideal design and installation process is transparency from all parties. If the client brings in seismic engineer at the concept development stage, seismic requirements can be discussed with the designer before they start. Then, an early design review can be performed to assess whether the design is suitable (from a seismic perspective).
Following this step, site visits for a pre-installation walkdown can be arranged, where the team (designers/ client/operators) can walk and talk the route, looking for any potential concerns, and dealing with any necessary design changes before the installation actually begins.
Then, depending upon the size of the project, interim walkdowns can be performed to identify and resolve any site-led changes or unforeseen installation difficulties, such as heavy rebar preventing anchorage, or scaffolding that has been put up in such a manner that it prevents the necessary drill from being used. If this rigorous approach to seismic qualification is adopted, when it comes to the post- installation walkdown, it’s more of a confirmatory sign-off.
Although it may seem like an unnecessary cost at the beginning of a job, in the long run, it can prevent issues that may lead to delays in the start-up of a facility and save organizations large-scale costs at the end of a job.
Author: Andrew Buckley, Principal Engineer, ABS Group, UK
