By Brian Smith, Project Manager
Hydrostatic testing of ductile iron pipe is a fairly normal part of the installation process. It’s the most common method for testing pipes for strength and leaks. Typically, the pipe is laid on bedding material (for example, dirt), the ends are capped, the pipe is filled with water and the pressure increased. The pipeline is allowed to sit for a specified duration and then we check for leaks. If there’s no leaks, we drain the pipe, and finish covering the pipe with material.
Vogel Bros. was working at a water treatment plant in Florida on a project that required the pipeline to be encased in concrete. The pipe was going to need to be tested before it was encased. This meant the pipe would need to be suspended within a reinforced steel cage for the testing rather than laid on the bedding material. Each spool of 42” diameter ductile iron pipe weighs approximately 10,000 lbs. Once water is added to the pipe for testing, the weight of each spool is more than double, weighing just over 22,000 lbs. How were we going to support the weight of the suspended pipe within the cage and make sure the environment was safe for our workers?
The project team looked at ways to support the pipe within the cage. The reinforcing cage did not provide a smooth surface beneath the pipe, so the support system needed to be something that could be left in place. Wood dunnage would span the reinforced steel and provide the smooth surface, but was not a viable option, as the dunnage could not be removed for the encasement.
Another option proposed that seemed viable was utilizing concrete blocks and bricks to support the empty pipe. We had to break the blocks and work them in between the reinforced steel to support the pipe. This appeared to be sufficient until placement of the third pipe spool. That’s when the concrete blocks started to crumble under the weight (and we hadn’t even started adding water!). This was now a big safety issue, as we could not have workers in the excavation with limited movement and not be certain the support system was safe. We added additional blocks to support the empty pipe, but we knew that another support system would be needed prior to adding water.
The project team assessed the challenge and discussed possible solutions. Ultimately, it was determined that since the pipeline was to be encased in concrete, the best support would be to begin placement of the concrete encasement beneath the pipe while blocking the joints. This would provide complete support of each pipe spool with the water added and throughout the testing, while still allowing inspection of each joint. If there was an issue, the pipe could still be accessed to make repairs. For this project the pipe tested on the first try and maintained elevation. This solution allowed us to leave the pipeline full of test water while additional ancillary pipelines were added and tested. The success we had on this project has encouraged us to use this same method on all under slab piping projects.