Construction Defects

Chilled Water Pipe Joint Failure

Construction Defects

Chilled Water Pipe Joint Failure

Construction Defects

Chilled Water Pipe Joint Failure

A new building project at a major university in Virginia required the replacement of an existing section of 18” diameter underground chilled water supply and return piping.  As the new chilled water supply piping was being filled at the completion of the project, one of the pipe joints failed.  The resultant leak caused extensive erosion, damage to adjacent piping due to settling, and flooded a nearby medical facility.

Flooded Medical Facility

According to project documentation, the new chilled water lines had undergone and passed all required pressure testing.  The new chilled water piping had also passed all required inspections by project engineers and the Authority Having Jurisdiction (AHJ).  Additionally, pre-incident and post-incident photos of the piping system provided no evidence that the failed joint had been improperly installed.

The replacement chilled water piping deviated from the mechanical building plans for various reasons.  In anticipation of such deviations, the project specifications included provisions to account for changes.  Namely, the specifications called for the installation of air vents at all high points in the underground chilled water piping system.  The mechanical building plans also provided piping details for such vents.   Review of the as-built plans revealed that there were two high points in each of the underground supply and return lines; however, no vents were installed in the underground lines.

Through analysis and investigation, the EIS engineer determined that when the valve was initially opened to fill the chilled water supply line, a pocket of air became trapped at each of the high points in the system.  As the valve was further opened and the flow of water increased, the mass of air trapped at the high points began to break apart and travel downstream.  This created a discontinuous flow in the pipe known as a “slug flow”, which is characterized as pockets of air-liquid mixture, followed by a wave or ‘slug’ of nearly pure water.  In established flow of chilled water in a pipe, there is no change in density of the fluid moving through the pipe, and therefore, no net change in momentum or net change in the forces acting on the piping.  Contrarily, in a slug flow, the air moving through the piping has a different density than the water.  This results in unbalanced forces being applied to the piping system, particularly at changes in direction.  The slug flow in this instance effectively caused a wall of water to slam into the pipe elbow at the subject joint, creating movement in the fitting and causing the joint to fail.     

Failed Pipe Joint

A new building project at a major university in Virginia required the replacement of an existing section of 18” diameter underground chilled water supply and return piping.  As the new chilled water supply piping was being filled at the completion of the project, one of the pipe joints failed.  The resultant leak caused extensive erosion, damage to adjacent piping due to settling, and flooded a nearby medical facility.

Flooded Medical Facility

According to project documentation, the new chilled water lines had undergone and passed all required pressure testing.  The new chilled water piping had also passed all required inspections by project engineers and the Authority Having Jurisdiction (AHJ).  Additionally, pre-incident and post-incident photos of the piping system provided no evidence that the failed joint had been improperly installed. 

The replacement chilled water piping deviated from the mechanical building plans for various reasons.  In anticipation of such deviations, the project specifications included provisions to account for changes.  Namely, the specifications called for the installation of air vents at all high points in the underground chilled water piping system.  The mechanical building plans also provided piping details for such vents.   Review of the as-built plans revealed that there were two high points in each of the underground supply and return lines; however, no vents were installed in the underground lines. 

Through analysis and investigation, the EIS engineer determined that when the valve was initially opened to fill the chilled water supply line, a pocket of air became trapped at each of the high points in the system.  As the valve was further opened and the flow of water increased, the mass of air trapped at the high points began to break apart and travel downstream.  This created a discontinuous flow in the pipe known as a “slug flow”, which is characterized as pockets of air-liquid mixture, followed by a wave or ‘slug’ of nearly pure water.  In established flow of chilled water in a pipe, there is no change in density of the fluid moving through the pipe, and therefore, no net change in momentum or net change in the forces acting on the piping.  Contrarily, in a slug flow, the air moving through the piping has a different density than the water.  This results in unbalanced forces being applied to the piping system, particularly at changes in direction.  The slug flow in this instance effectively caused a wall of water to slam into the pipe elbow at the subject joint, creating movement in the fitting and causing the joint to fail.     

Failed Pipe Joint

A new building project at a major university in Virginia required the replacement of an existing section of 18” diameter underground chilled water supply and return piping.  As the new chilled water supply piping was being filled at the completion of the project, one of the pipe joints failed.  The resultant leak caused extensive erosion, damage to adjacent piping due to settling, and flooded a nearby medical facility.

Flooded Medical Facility

According to project documentation, the new chilled water lines had undergone and passed all required pressure testing.  The new chilled water piping had also passed all required inspections by project engineers and the Authority Having Jurisdiction (AHJ).  Additionally, pre-incident and post-incident photos of the piping system provided no evidence that the failed joint had been improperly installed. 

The replacement chilled water piping deviated from the mechanical building plans for various reasons.  In anticipation of such deviations, the project specifications included provisions to account for changes.  Namely, the specifications called for the installation of air vents at all high points in the underground chilled water piping system.  The mechanical building plans also provided piping details for such vents.   Review of the as-built plans revealed that there were two high points in each of the underground supply and return lines; however, no vents were installed in the underground lines. 

Through analysis and investigation, the EIS engineer determined that when the valve was initially opened to fill the chilled water supply line, a pocket of air became trapped at each of the high points in the system.  As the valve was further opened and the flow of water increased, the mass of air trapped at the high points began to break apart and travel downstream.  This created a discontinuous flow in the pipe known as a “slug flow”, which is characterized as pockets of air-liquid mixture, followed by a wave or ‘slug’ of nearly pure water.  In established flow of chilled water in a pipe, there is no change in density of the fluid moving through the pipe, and therefore, no net change in momentum or net change in the forces acting on the piping.  Contrarily, in a slug flow, the air moving through the piping has a different density than the water.  This results in unbalanced forces being applied to the piping system, particularly at changes in direction.  The slug flow in this instance effectively caused a wall of water to slam into the pipe elbow at the subject joint, creating movement in the fitting and causing the joint to fail.     

Failed Pipe Joint