Corrosive Injection and Mixing Points

Injection/Mixing point Circuits typically include the piping of the fluid being injected, upstream of the injection area, and downstream of the injection area.

Define Asset – Step 1

See Step 1.

Injection/Mixing Points are defined as Potentially Corrosive or Non-Corrosive:

• Potentially Corrosive: The mixing of two streams is potentially corrosive when the blending or IP/MP failure could result in accelerated CRs that may compromise piping or Equipment integrity. Also included are IP/MPs where a sudden, short, change in process conditions results in high-rate episodic degradation. Thermal fatigue should be considered (see Thermal IP/MP).

• Non-Corrosive: The mixing of two streams is non-corrosive when significant interaction is not possible, or the likelihood is low for compromising piping/Equipment integrity or operability. Non-corrosive IP/MPs should be monitored as part of the main Piping System.

When injection is into pressure vessels and process Equipment, it is recommended not be set up as IP Circuits, but instead include the inspection as part of the Equipment inspection plan. These are areas of potentially high corrosion.

For piping, Corrosive IPs and Corrosive MPs can be modelled as separate Components in IMS. On this level the RBI Analysis can then take place. The IP/MP Component is modelled separately due to unique operating characteristics (e.g., lower temperature than upstream piping), significantly different potential/actual CRs, and critical design and operation of the injection quill. These parameters effect the Consequence and Likelihood of failure, and thus the total risk.

Potentially Corrosive IP/MPs should be identified in IMS as unique corrosion Circuits.

Assign DMs to Component – Step 3

See Step 3.

For Corrosive IP/MPs, you can assign the IP Analysis or MP Analysis respectively, rather than an actual Degradation Mechanism (DM).

RL – Step 6 & Step 11

See Step 6 and Step 11.

RL is not applicable, but the RL tab can be used to enter a Legal/Local Interval. This may influence the NID.

StF – Step 7

See Step 7.

The difference between the Potential Corrosive Rates (PCR) and the Design Corrosion Rate (DCR) of the main flowing pipe determines Corrosive IP/MP StF. Susceptibility to Fail is the vulnerability to actual degradation as compared to the degradation expected per design.

IMS uses the following deltas to determine the StF:

• A: > 2 mpy (> 0.05 mm/y)

• B: 2-5 mpy (0.05 - 0.13 mm/y)

• C: 5-10 mpy (0.13 – 0.25 mm/y)

• D: 10-20 mpy (0.25 – 0.5 mm/y)

• E: < 20mpy (<0.5mm/y)

Confidence – Step 10

See Step 10.

The Confidence Assessment  it not applicable for Corrosive MP/IPs.

IS and MII – Step 11 & Step 12

See Step 11 and Step 12.

The following table is implemented in IMS to determine the IS class (A, B, C, D, E, or F) and MII. When the IP/MP classification is E, S-RBI determines if the Consequence selected is RAM 2 or 3, hence automatically showing the 8- or 10-year interval.

Inspection Strategy lookup table for Corrosive IP/MP:

Assign RBI results to Corrosion Schedule – Step 12

See Step 12.

As mentioned, Corrosive and Thermal IP/MPs should be identified as unique corrosion Circuits. CML’s must be established based on the “primary zone” (requiring more extensive inspection) and the “secondary zone”, which is the outer boundaries of the injection Circuit. All the CMLs should be inspected on both zones.

The Risk Classification is used to determine the maximum time interval between inspections. This risk classification is used by IMS to automatically set the maximum time interval for the Circuit Corrosion Schedule. The Circuit detail should be tagged according its IS class (A,B,C,D,E, or F – see IS table above) by assigning a Special Emphasis to it.

Static Mixers

Inspect as part of IP/MP inspection strategy. If the static mixer is not related to a Corrosive IP/MP, then it should be "stand-alone" Equipment. If it is part of an IP/MP, then it should be managed as part of the Piping System, but it should have an inspection strategy related to the IP/MP. A damaged static mixer will increase corrosion issues downstream of the IP/MP that might not have been accounted for during the corrosion assessment of the IP/MP.

Some static mixers are internally alloyed, so it might need a corrosion Circuit different from the upstream pipe and sometimes different from the downstream side of the IP/MP. The Corrosion Material Engineer should be consulted to determine the best Inspection Strategy.

Part of the Inspection Strategy could be RT profile just to look for internal damage or pulling spool for internal visual inspection.

Thermal Sleeves 

Inspect as part of IP/MP inspection strategy. A damaged thermal sleeve will increase likelihood of cracking of the IP/MP.

Spray Nozzle / Quills

Inspect as part of IP inspection strategy. A damage spray/nozzle or quill will probably increase the CR of the IP.