Tube Rupture Credibility Assessments (TRCA)

Apply Equity Engineering’s tube rupture credibility assessment (TRCA) methodology to determine whether a full-bore tube rupture is credible. API 521-compliant. PE-stamped. 200+ assessments completed. 99% non-credible.

Download the Tube Rupture Credibility Assessment (TRCA) Overview here.

The most cost-effective relief device is the one you can prove you don’t need.

A tube rupture credibility assessment (TRCA) determines whether a full-bore tube rupture is credible for a specific heat exchanger – and in over 99% of TRCAs we performed, it wasn’t credible. Often when a PHA or pressure relief system revalidation identifies a tube rupture overpressure scenario, the default response is to install new hardware – a potential $50,000 to $500,000 capital project requiring a shutdown and 6 to 12 months to execute.

There is a better and more cost-effective way. API 521 states if a rigorous engineering analysis can prove that a full-bore tube rupture is non-credible for your specific exchanger, dedicated overpressure protection for that scenario is not required. Equity Engineering’s TRCA evaluates whether the scenario is credible by considering design, metallurgy, inspection history, and operating conditions.

We’ve conducted more than 200 TRCAs over 18 years and helped refineries and petrochemical facilities avoid millions in unnecessary capital expenditure.

Before committing capital to any relief system upgrade for the tube rupture case, perform a TRCA.

When Equity determines that a tube rupture scenario is non-credible, that conclusion is backed by engineers who helped shape the API 521 standard and actively work to improve its guidance today.

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

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