Pipe Support Small Bore Connection ⬇️
A challenging task regarding pipe support design is supporting of small bore connections (SBC) with a lump mass at the end (e.g. pipe vent/drain, instruments connection etc.). With this article, Pipe Support Verification’s aim is to give the basic thoughts of doing a good SBC support design.
We can divide the supporting of SBC in two categories:
Static effects – meaning the lump mass needs supporting because of large static loads.
Dynamic effects – meaning vibrations in the SBC caused by flow induced vibration (FIV), acoustic induced vibration (AIV) or equipment induced vibration (EIV).
The most challenging is the supporting due to dynamic effects. To find the SBC that require bracing, we need to evaluate where it is likely that vibrations can occur. Regarding FIV, the piping stress group usually do a FIV screening to find the LOF parameter (likelihood of failure) for the pipe system. If this parameter is above the limit set for the project, bracing should be provided for all SBC in that system. A typical limit can be a LOF>0,5 for medium stiff system. In addition to FIV we need to evaluate other sources of vibrations such as AIV (typ. flare system) or EIV (Equipment that causes vibrations in connected pipe systems). This to find which SBC that need bracing.
When the SBC that need bracing has been concluded, the next question is how? There are several types of bracing. Clamped, Welded sections, welded plates (knee-braces) etc. How they are attached to the SBC does also vary.
A challenging task regarding pipe support design is supporting of small bore connections (SBC) with a lump mass at the end (e.g. pipe vent/drain, instruments connection etc.). With this article, Pipe Support Verification’s aim is to give the basic thoughts of doing a good SBC support design.
We can divide the supporting of SBC in two categories:
Static effects – meaning the lump mass needs supporting because of large static loads.
Dynamic effects – meaning vibrations in the SBC caused by flow induced vibration (FIV), acoustic induced vibration (AIV) or equipment induced vibration (EIV).
The most challenging is the supporting due to dynamic effects. To find the SBC that require bracing, we need to evaluate where it is likely that vibrations can occur. Regarding FIV, the piping stress group usually do a FIV screening to find the LOF parameter (likelihood of failure) for the pipe system. If this parameter is above the limit set for the project, bracing should be provided for all SBC in that system. A typical limit can be a LOF>0,5 for medium stiff system. In addition to FIV we need to evaluate other sources of vibrations such as AIV (typ. flare system) or EIV (Equipment that causes vibrations in connected pipe systems). This to find which SBC that need bracing.
When the SBC that need bracing has been concluded, the next question is how? There are several types of bracing. Clamped, Welded sections, welded plates (knee-braces) etc. How they are attached to the SBC does also vary.
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In the inspection of spring hangers, we will:
search for signs of visual cracks, fractures, or corrosion of the spring casing and the following:
(1) beam attachment
(2) pin
(3) spring hanger attachment
(4) pipe clamp attachment
(5) weldless eye nut/clevis
(6) threaded rod
(7) turnbuckle
(8) nuts
(9) spring coil
(10) position
check the turnbuckle
(7) if present, lock nuts
(8), and all other threaded items to ensure they are secured and fastened with full thread engagement compare the position of the coil
(10) with the hot/cold load indicator and operating range of the spring
check the mobility of the load column
(11)
In the inspection of spring hangers, we will:
search for signs of visual cracks, fractures, or corrosion of the spring casing and the following:
(1) beam attachment
(2) pin
(3) spring hanger attachment
(4) pipe clamp attachment
(5) weldless eye nut/clevis
(6) threaded rod
(7) turnbuckle
(8) nuts
(9) spring coil
(10) position
check the turnbuckle
(7) if present, lock nuts
(8), and all other threaded items to ensure they are secured and fastened with full thread engagement compare the position of the coil
(10) with the hot/cold load indicator and operating range of the spring
check the mobility of the load column
(11)
INSPECTION CHECKLIST EXPANSION JOINTS
1- Expansion Joint Bellows
check for signs of leakage or a loss of pressure
2- inspect for any distortion or yielding of anchors, hardware, bellows, and piping connection points
3- observe for any unanticipated movement of piping due to pressure
4- inspect for evidence of instability (squirm), distortion or damage in the bellows convolutions
5- check the expansion joint, the guides, and other moveable parts of the system for evidence of binding
6- check for misalignment of the expansion joint unit
7- check for vibration damage
1- Expansion Joint Bellows
check for signs of leakage or a loss of pressure
2- inspect for any distortion or yielding of anchors, hardware, bellows, and piping connection points
3- observe for any unanticipated movement of piping due to pressure
4- inspect for evidence of instability (squirm), distortion or damage in the bellows convolutions
5- check the expansion joint, the guides, and other moveable parts of the system for evidence of binding
6- check for misalignment of the expansion joint unit
7- check for vibration damage
🈁 Stress Analysis Review of Critical Fire Water System Sections
In this case study, a number of critical sections in an already installed fire water system were selected for review. At the time of the analysis, earlier on-site interventions had already been made, motivated by pipe failures. The analysis aimed to determine if additional interventions were necessary.
In this case study, a number of critical sections in an already installed fire water system were selected for review. At the time of the analysis, earlier on-site interventions had already been made, motivated by pipe failures. The analysis aimed to determine if additional interventions were necessary.
⬇️ Analysis
Based on the isometric drawings, a number of critical sections were identified and analyzed using the piping analysis software CAESAR II. A selection process revealed typical layouts and designs for these critical sections. An important aspect of the analysis was the sensitivity of the piping to settlements, especially of thrust blocks.
Based on the isometric drawings, a number of critical sections were identified and analyzed using the piping analysis software CAESAR II. A selection process revealed typical layouts and designs for these critical sections. An important aspect of the analysis was the sensitivity of the piping to settlements, especially of thrust blocks.
⬇️ Results
The analysis results showed that thrust blocks had been adequately sized concerning pressure thrust. Furthermore, it was observed that stress problems did not occur in piping that had been joined using coupling joints. For one critical section where coupling joints were used, the effect of settlement of thrust blocks was examined. It was concluded that piping with coupling joints is not sensitive to this problem due to the additional flexibility provided by the joints.
The analysis results showed that thrust blocks had been adequately sized concerning pressure thrust. Furthermore, it was observed that stress problems did not occur in piping that had been joined using coupling joints. For one critical section where coupling joints were used, the effect of settlement of thrust blocks was examined. It was concluded that piping with coupling joints is not sensitive to this problem due to the additional flexibility provided by the joints.
The most critical observations from the analysis were:
# The occurrence of high stresses at the elbows directly below the hydrants.
# The occurrence of high stresses in the case of settlements of thrust blocks.
# The occurrence of high stresses in the case of settlements of the concrete slabs supporting the hydrants.
# The occurrence of high stresses at the elbows directly below the hydrants.
# The occurrence of high stresses in the case of settlements of thrust blocks.
# The occurrence of high stresses in the case of settlements of the concrete slabs supporting the hydrants.
❗️It was shown in this assessment that the settlement of thrust blocks may be the main reason for high-stressed regions to occur. However, based on the knowledge that most settlement of thrust blocks would occur in the period immediately following installation, and the fact that no such failure had occurred after the last on-site intervention, a large-scale preventative intervention was not deemed necessary.
🔔Lessons Learned from Large-Diameter Pipe Failure Case Studies
⤵️. Failures of large diameter pipes can cause significant social, environmental and economic impacts. The actual failure mechanisms of buried pipes are difficult to isolate because many external and internal factors are commonly involved. Moreover, the major pipe breaks occur below the ground and the root cause of failure may be masked by the violent nature of the break. Detailed investigations were undertaken to examine and understand the failure mechanisms of buried large diameter cast iron water pipe breaks. We used various approaches to gathering field evidence from failed as well as unfailed pipes, numerical simulations, field instrumentation and full-scale laboratory pipe burst testing. Large diameter pipes tend to fail predominantly by longitudinal fracture. The failure mechanisms involving longitudinal fractures indicated that a large corrosion patch in the pipe barrel is commonly needed for pipe failure. This finding is in contrast to the belief that small pits are mostly responsible for failures. This means that many of the current condition assessment techniques currently targeting the detection of pits in pipes need to focus on the detection of larger patches of corrosion. The research also found that pipes fail by developing a crack first within a corrosion patch that could lead to water leakage until the crack grows sufficiently long to cause a major break. This concept is referred to as “leak before break” (LBB) for cast iron pipes. This concept can potentially be used for failure prevention of critical pipelines through improved leak detection.
⤵️. Failures of large diameter pipes can cause significant social, environmental and economic impacts. The actual failure mechanisms of buried pipes are difficult to isolate because many external and internal factors are commonly involved. Moreover, the major pipe breaks occur below the ground and the root cause of failure may be masked by the violent nature of the break. Detailed investigations were undertaken to examine and understand the failure mechanisms of buried large diameter cast iron water pipe breaks. We used various approaches to gathering field evidence from failed as well as unfailed pipes, numerical simulations, field instrumentation and full-scale laboratory pipe burst testing. Large diameter pipes tend to fail predominantly by longitudinal fracture. The failure mechanisms involving longitudinal fractures indicated that a large corrosion patch in the pipe barrel is commonly needed for pipe failure. This finding is in contrast to the belief that small pits are mostly responsible for failures. This means that many of the current condition assessment techniques currently targeting the detection of pits in pipes need to focus on the detection of larger patches of corrosion. The research also found that pipes fail by developing a crack first within a corrosion patch that could lead to water leakage until the crack grows sufficiently long to cause a major break. This concept is referred to as “leak before break” (LBB) for cast iron pipes. This concept can potentially be used for failure prevention of critical pipelines through improved leak detection.
🔔The Danger of Piping Failure Due to Acoustic-Induced Fatigue in Infrequent Operations
⤵️ Failure in piping due to acoustic-induced fatigue can be considered catastrophic as it could happen only after a few minutes of operation. Acoustic-induced fatigue occurs mainly in gas piping systems with high velocity where high energy is dissipated through pressure reducing stations and pipe branch connections. It usually results in pipe through wall longitudinal cracks, pipe detachment from saddle supports, and complete shear off of branch connections. There are existing design criteria to avoid acoustic-induced fatigue based on comparison of generated power level to an acceptable power level. This criterion is normally used for the design of pressure relief and flare piping where high gas velocity exceeding 50% of the speed of sound (i.e., 0.5 Mach) is expected. However, acoustic-induced fatigue has been experienced in systems due to intermittent operations. Two case studies are presented.
1- The first one is during a steam-out operation to clean a newly constructed steam header. During the cleaning operation, an orifice plate was used to control the flow in the steam header. Several pipe vents and drains failed due to fatigue in less than 1 h.
2- The second case is for drainage of compressed natural gas during process upset condition. Because of the high level buildup in the liquefied gas separator vessel, the drain valve was opened to release the pressurized liquefied gas to the relief system to reduce the level buildup. Wall cracks and several pipe support detachments were found in the system after the upset condition.
⤵️ Failure in piping due to acoustic-induced fatigue can be considered catastrophic as it could happen only after a few minutes of operation. Acoustic-induced fatigue occurs mainly in gas piping systems with high velocity where high energy is dissipated through pressure reducing stations and pipe branch connections. It usually results in pipe through wall longitudinal cracks, pipe detachment from saddle supports, and complete shear off of branch connections. There are existing design criteria to avoid acoustic-induced fatigue based on comparison of generated power level to an acceptable power level. This criterion is normally used for the design of pressure relief and flare piping where high gas velocity exceeding 50% of the speed of sound (i.e., 0.5 Mach) is expected. However, acoustic-induced fatigue has been experienced in systems due to intermittent operations. Two case studies are presented.
1- The first one is during a steam-out operation to clean a newly constructed steam header. During the cleaning operation, an orifice plate was used to control the flow in the steam header. Several pipe vents and drains failed due to fatigue in less than 1 h.
2- The second case is for drainage of compressed natural gas during process upset condition. Because of the high level buildup in the liquefied gas separator vessel, the drain valve was opened to release the pressurized liquefied gas to the relief system to reduce the level buildup. Wall cracks and several pipe support detachments were found in the system after the upset condition.