TUBE RUPTURE SCENARIOS
Eliminate Risk & Improve PRV Design
Heat exchangers require pressure relief valves (PRVs) that control the high-pressure fluid moving into the low-pressure side of a heat exchanger and manage any overpressure events. One of the main challenges is that pressure spikes can disperse within 10 to 15 milliseconds of a tube rupture or overpressure scenario, yet spring-loaded PRVs open within 20 to 50 milliseconds. This minuscule delay can cause significant damage.
Facilities need to design for tube rupture scenarios or conduct an analysis to prove the credibility of a tube rupture occurring. At Equity, we have developed a proprietary tube rupture credibility assessment (TRCA) methodology that determines the credibility of a tube rupture scenario by accounting for the exchanger design and the process conditions.
Conducting a TRCA will save money, increase the safety of the pressure relief system (PRS) and heat exchangers, and improve the PRS design. The rigorous analysis of the heat exchanger design will outline any potential process changes, potential damage mechanisms, and material upgrades or modifications to address a full-bore tube rupture.
What is a Tube Rupture?
Undetected corrosion, fatigue, or brittle fracture in piping connected to a heat exchanger can result in a tube leak or a full-bore tube rupture. This failure will cause the high-pressure fluid to expand into the low-pressure side through the ruptured tube bore, creating a pressure surge on the low-pressure side. The pressure will quickly spike, and the PRVs may not respond quickly enough, causing an overpressure scenario.
Equity's Tube Rupture Credibility Analysis (TRCA)
Our team performs a dynamic heat exchanger analysis to eliminate the potential for tube ruptures at a facility. Following API 520 guidelines, we use our proprietary “TBREAK” software to assess the tube rupture scenario and simulate the transient release of fluid from the high-pressure side to the heat exchanger to assess the impact and requirements for pressure relief protection on the low-pressure side.
We recommend conducting a TRCA before responding to an overpressure revalidation study and spending any capital money.
Equity's TRCA Workflow
The rigorous analysis of the heat exchanger design will outline any potential process changes, potential damage mechanisms, and material upgrades or modifications to address a full-bore tube rupture.
Our workflow includes:
- Tube vibration analysis of the exchanger bundle
- Review of shell and bundle entrance velocities to assess erosion potential
- Assessment of the tube-to-tubesheet joint strength
- Metallurgical analysis to assess the likelihood for environmental stress corrosion cracking (SCC), brittle fracture, and creep
- Thermal/mechanical fatigue assessment for those exchangers that are expected to be exposed to frequent variable operating conditions
- Corrosion analysis to assess the severity of any corrosion mechanisms
- Review of the inspection programs and techniques used to determine whether they are adequate to assess the onset of cracking problems or to acquire evidence of tube pullout
Case Study: Determine the Path Forward for Tube Rupture Mitigation
Issue: The client identified a need to redesign the existing pressure relief system for a heat exchanger so it could adequately handle the full-bore tube rupture scenario.
Solution: We performed a rigorous analysis of the heat exchanger design and process conditions to determine whether the exchanger was susceptible to a full-bore tube rupture via tube vibration, erosion, applicable damage mechanisms, fatigue, tube pullout, or tube buckling.
Result: The full-bore tube rupture scenario was determined to be non-credible for the exchanger, thereby eliminating the need to redesign the existing pressure relief system. We recommended incorporating a leak detection system and regular tube inspection to mitigate the client’s concern of any long-term damage that could lead to a full-bore tube rupture.
API 521 Tube Rupture Mitigation Methods
API STD 521, Pressure Relieving and Depressuring Systems is the industry standard (RAGAGEP) for PRS design. API 521 discusses several possible overpressure scenarios and offers guidance regarding the design of overpressure protection of heat exchangers for the tube rupture scenario, including two mitigation methods:
Mitigation Method 1
- Assumes a full-bore overpressure scenario is credible
- Conducts dynamic or transient analysis of rupture flow to determine magnitude of pressure spike
- Results in modifications to the relief system
- Relief protection on low-pressure side is adequately sized to handle rupture flow
- Not always practical to increase the design side of the low-pressure exchanger side
Mitigation Method 2
- Analysis to eliminate tube rupture scenario
- Performs detailed analysis to demonstrate the likelihood of a tube rupture scenario
- Considers heat exchanger design and process fluid
- A modified inspection program will target the locations or damage mechanisms that could result in a full-bore tube rupture
- Applies principles of risk to tube rupture scenario analysis and inspection program
Pressure Relieving Systems Expertise
The process technology team has used Equity’s proprietary tube rupture credibility assessment (TRCA) in more than 60 applications to resolve issues related to heat exchanger tube ruptures. Our team of internationally recognized experts in pressure relief system design, optimization, and installation will provide practical recommendations to increase safety and maximize reliability.
Our experts:
- Have 100+ years of experience
- Have served as API 520 task force chairman for more than 25 years
- Are the primary authors of WRC 528 and WRC 562
- Serve as lead investigators on API 579 and API 571
