RBI Example 1 - Risk Based Inspection Analysis of a Reactor Casing

Background

This example demonstrates how to perform a risk based inspection analysis using the RBI software.

For this example, you will be analyzing a reactor casing that was installed on March 13, 2009 with a planned replacement date of March 13, 2026. The reactor is subject to general thinning corrosion and possible amine cracking. On average, the reactor contains 15 tons of liquid ammonia with the upstream connected equipment containing another 35 tons of liquid ammonia. Management estimates that the loss of production due to reactor downtime is $100,000 per day. The acceptable safety risk is 2,500m2 and the acceptable financial risk is $3 million. You must determine if the reactor requires any further inspections before the planned replacement date.

 

Click here to see the full reactor details
  • The reactor is located in Budapest, Hungary.
  • The climate is considered to be temperate with an atmospheric temperature of 25°C.
  • The material of construction is carbon steel with no cladding, lining or insulation.
  • The standard operating temperature is -20°C and the standard operating pressure is 1.0 MPa.
  • The component was installed on 3/13/2009 and is scheduled to be replaced on 3/13/2026.
  • The reactor diameter is 2 m.
  • The minimum wall thickness per code is 5 mm while the corrosion allowance by code is 25 mm.
  • The possible damage factors are general thinning corrosion and SCC - Amine Cracking.
  • The online monitoring system uses electrical resistance probes; however, the corrosion mechanism is not specified within API 581.
  • Wall measurements have been performed three times, with the last one performed on 3/13/2016.
  • The last inspection for amine cracking was performed on 1/5/2016 and it found that the reactor was exposed to lean amines (type unknown) and found some minor internal cracking.
  • The component is not stress relieved or heat traced, and it was not steamed-out during the last inspection.
  • All previous inspections are considered to be poorly effective based on API 581.
  • The last measured wall thickness was 20 mm with an estimated corrosion rate of 1.0 mm / year.
  • On average, the reactor contains 15 tons of liquid ammonia with the upstream connected equipment containing another 35 tons of liquid ammonia.
  • The detection system uses monitors to detect the presence of fluid outside the reactor. The isolation system is designed to allow the operators to shut down the system from the control room.
  • The process fluid is pure ammonia.
  • The fire system is a deluge system with monitors.
  • The personnel density around the unit is estimated to be about 1 personnel every 100 m2.
  • The cost of equipment is estimated to be ~$500,000 per 100 m2.
  • Management estimates that the loss of production due to reactor downtime is $100,000 per day.
  • The cost of injury to personnel is estimated to be $100,000 while there is no real environmental cleanup cost associated with the ammonia.
  • The acceptable safety risk is 2,500 m2 and the acceptable financial risk is $3 million.

Analysis

Step 1: Create the system hierarchy.

Step 2: Enter the general properties.

Step 3: Select the applicable damage factors that apply to the component.

Step 4: Enter the damage factor properties.

Step 5: Enter the consequence properties.

Step 6: Calculate the component results and review the values shown next. (Note that most of the dates shown in the following pictures are based on the date when the analysis was performed in the sample project. If you repeat the analysis from scratch, or if you recalculate, the specific dates in your results will be different.)

As shown above, the Area Based Risk exceeds the risk target on November 19, 2021. And, as shown in the Recommended Inspection(s)node, on that date you must perform two inspections: one for the thinning damage and one for amine cracking damage. These must be at least poorly effective (a class "D" inspection). If the inspections do not find anything out of the ordinary (i.e., everything is found to be as currently predicted), then the potential risk is lowered to an acceptable level by the time the reactor is due to be replaced.

The following plot shows these dates graphically.

Discussion

Based on the analysis the reactor will require additional inspections before the planned replacement date, but as long as they are at least poorly effective, and nothing out of the ordinary is found, then the area and financial risks will likely remain within the limits determined by the management.