Thermal Injection and Mixing Points

Material

This is the material of construction for the receiving pipe at a thermal mix point.

The material (Carbon Steel & Low Alloy Steel vs Austenitic Stainless Steel) influences the Thermal Conductivity and Thermal Expansion Coefficient.

-

Temperature difference (DT)

Temperature difference between the injection and receiving process streams.

Yes

Cycling frequency

Possible types of thermal cycles at a TMP:

• Cycles associated with the on/off cycle when the injected flow is started and stopped.
• Cycles associated with the fluctuation in local fluid temperature at the pipe wall due to turbulent interaction between the two mixing fluids.

The thermal stress associated with an on/off cycle is typically only a concern for TMPs frequently used on an intermittent basis, where the number of thermal cycles due to the on/off cycle would be significant (i.e., hundreds to thousands of cycles).

The frequency and amplitude of the variation in local fluid temperature at the pipe wall is difficult to estimate, but the total number of cycles may be in the order of millions per year.

Note: For major process variations like start-ups, changes in processing temperatures, etc., the total number of cycles will be in the orders of thousands. This is covered by a different DM: Fatigue by Cyclic Service.

-

Phase

Phase (liquid, vapor/gas, multi-phase) and composition (water, steam, hydrocarbons) of the two process streams.

Note: This is difficult to monitor as an IOW, but should be a consideration as part of an MOC review (i.e., for changes in operating parameters that may affect fluid phase, or changes that may lead to different fluid composition)

Yes

Design

Check if a thermal quill or sleeve is required and installed per design requirements.

-

Flow Rate Ratio (FRR)

Mass Flow Rate Ratio (FRR) of the two mixing process streams.

Yes

Type 1 (T1)

TMPs that do not exceed the ΔT thresholds as per design requirements and do not require IOWs to maintain this status.

Type 2 (T2)

TMPs that do not exceed the ΔT thresholds as per the design requirements but require IOWs to maintain this status.

An IOW is considered where the ΔT is near the threshold, and “process creep” or planned process changes could cause ΔT to exceed the threshold. An IOW (standard limit) should then proactively monitor the mix point operation. Consequence of Failure (CoF) can help decide whether to implement an IOW, where IOW’s are intended for TMPs with potential RAM3 and higher CoF.

Type 3 (T3)

TMPs with compliant hardware design (but no thermal sleeve) where IOWs are required to maintain this status.

For T3 TMPs the hardware Barrier is premised on maintaining operation below threshold ΔT or mass FRR. If “process creep” or planned process changes result in an increase in ΔT or FRR that exceeds the threshold, the TMP design would now require thermal sleeve protection. An IOW (standard limit) should then proactively monitor the mix point operation. Consequence of Failure (CoF) can help decide whether to implement an IOW, where IOW’s are intended for TMPs with potential RAM3 and higher CoF.

Type 4 (T4)

TMPs with compliant hardware design where IOWs are not required to maintain this status (i.e., both a thermal quill and thermal sleeve are installed).

Type 5 (T5)

TMPs where the hardware is not compliant with design.

Type 6 (T6)

TMPs which are operating outside the scope of design because the process fluid composition contains more than 10 wt% liquid water or steam in one or both of the process streams.

Phase of the injection and receiving streams

Should be based on the most credible condition.

Differential fluid temperature between the injection and receiving streams ΔT

The TMP’s ΔT should typically be based on the following criteria:

• If actual data is unavailable to trend historical fluid operating temperatures, a worst-case, credible ΔT should be established, including consideration of normal operating as well as start-up, upset, or shutdown conditions.
• Where operating data is available, a 5-year trend of actual fluid operating temperatures can be used to define the appropriate ΔT. When evaluating the temperature data, engineering judgement may be required:
• Large temperature peaks (i.e., outliers) which occur for a very short duration and occur infrequently should typically not be considered.
• Where multiple operating modes are present, it is advised to consider the worst-case time history when establishing the ΔT (under the assumption the fluid phases or mass flow rates do not change).

Design compliance

When evaluating the mechanical design of TMP hardware, the as-installed configuration should be compared to the design requirements.

With a design compliant TMP, the hardware has been designed and installed to minimize the thermal stress at the ID of the pipe wall in the mixing zone. This hardware is the primary Barrier that prevents thermal fatigue failure of the pressure boundary at the mix point. In these cases, the purpose of inspection is to verify that the thermal quill and if applicable, the thermal sleeve is still in good condition and functioning as designed.

For some design compliant designs (no thermal sleeve) an IOW (and proactive monitoring plan) is needed to prevent changes in actual operating conditions as compared to the conditions considered in the RBI assessment.

IOW requirement

See above.

Mass Flow Rate Ratio (FRR) of the injection and receiving streams

Should be based on the most credible condition. The FRR is not in the flow chart but helps determine the design compliance.

t_nom

This is the Nominal Wall Thickness.

TMP Proven or New

A TMP is Proven when:

• The TMP has operated at least 6 years of cumulative run time without evidence of thermal fatigue cracking;
• At least one highly effective cracking inspection has been performed after 6 years of cumulative operation; and
• No indications of thermal fatigue damage were observed during past inspections.

Confidence Rating for T4 TMPs (Design Compliant, but without IOWs)

Degradation mechanism can be properly controlled.

• Yes: For T4 type inherently true.

Relevant process parameters are reliably monitored.

• Yes: For T4 type inherently true

Reliable inspections were carried out.

• Yes: A highly effective inspection has been performed of the TMP hardware consistent with the intervals specified in the MII table below. When determining the appropriate inspection interval for the TMP hardware, the confidence assessment should be based on an evaluation of the DMs that could affect the integrity of the quill or sleeve, and the inspection history for these Components.
• No: No inspection has been performed, or an inspection has been performed prior to accumulating 6 years of total operating time, or an ineffective inspection has been performed.

Confidence Rating for T3 TMPs (Design Compliant with IOWs)

Degradation mechanism can be properly controlled.

• Yes: Relevant operating parameters are operating within the original design conditions.
• No: Relevant operating parameters are NOT operating within the original design conditions.

Relevant process parameters are reliably monitored.

• Yes: Relevant process variables have been defined based on the original design parameters. Relevant PTM limits are in place with continuous monitoring of the process variables. Relevant PTM exceedances are evaluated when they occur, and the potential impact to the TMP inspection strategy and TMP integrity is taken into consideration.
• No: Process variables are not defined, or process variables are not monitored.

Reliable inspections were carried out.

• Yes:
  • Cracking of Receiving Pipe: A highly effective inspection has been performed consistent with the intervals specified in the MII table below.
  • Thermal quill and thermal sleeve: Integrity is verified via at least one highly effective inspection. Typically, the TQ would be removed from the pipe for visual inspection, and other NDE performed as appropriate. Susceptibility of the thermal sleeve to corrosion, stress corrosion cracking, and vibration should also be considered when setting the inspection strategy and inspection interval for the TQ and thermal sleeve.
• No:
  • No inspection has been performed, or too early inspection has been performed and TQ & TS integrity is not verified via inspection, or
  • An ineffective inspection has been performed.

Confidence Rating for T5 TMPs (Not Design Compliant)

Degradation mechanism can be properly controlled.

• Yes: The 6-year operating history of the relevant process data (ΔT and FRR) has been analyzed and the following is confirmed to be true:
  • TMP has operated without failure for at least 6 years.
  • The ΔT data can be fit to a normal distribution with reasonable confidence (See Note 1). Meeting this criterion suggests that the relevant historical operating parameters are relatively constant, and the mix point can be considered a steady TMP.
• No:
  • Data to evaluate the relevant historical operating parameters is not available, or
  • The variation of ΔT and FRR are unsteady, or
  • TMP has operated without failure for less than 6 years. The statistical analysis indicates multiple modes of operation (mix points with two normal distributions that overlap), or operating hours associated with the “bins” at the higher-temperature ranges are insufficient to gain confidence in a Proven design.

Relevant process parameters are reliably monitored.

• Yes: Process variables have been defined based on a statistical review of historical operating data. Proactive monitoring limits are set as follows:
  • Mean ΔT and standard deviation are compared to the value calculated from the past operating data set, and the trend is monitored to detect changes in the mean ΔT and standard deviation over time.
  • The number of hours operating above the highest 2.5% of actual ΔT data is monitored and the trend is evaluated to detect an increase in the hours in this category over time.
  • Mass FRR is monitored to detect changes in average FRR, or changes in total mass FRR of the combined flow over time. Proactive monitoring limits are in place with continuous monitoring of the process variables. Trend exceedances or changes are evaluated when they occur, and the potential impact to the TMP inspection strategy and TMP integrity is taken into consideration.
• No: Process variables are not defined, or process variables are not monitored.

Reliable inspections were carried out.

• Yes:
  • Cracking of Receiving Pipe: At least one highly effective inspection has been performed after 6 years of operation. In some cases, a Proven design may still be installed with a TQ or a TS, but the design of the TQ or TS may not meet the full requirements of the design. However, in these cases, the Proven performance is based on the protection provided by the quill or sleeve and maintaining past performance in the future may be dependent on maintaining the integrity of the hardware.
  • Thermal Quill and Thermal Sleeve: TQ & TS integrity is verified via periodic inspection (interval based on susceptibility to corrosion or cracking, and vibration).
• No:
  • No inspection has been performed, or too early inspection has been performed and TQ & TS integrity is not verified via inspection, or
  • An ineffective inspection has been performed.

Notes:

1. Visual tools such as histograms are sufficient for evaluating the data fit to a Normal distribution. Mode splitting is required when multiple modes may be present. Significant local peaks in the distribution, specifically above the mean should be considered as unsteady.
2. When the TMP is defined to have a low confidence, a detailed analysis (i.e., CFD and FEA) can be performed to increase the confidence rating.

MII (yrs)

and IS

Confidence Rating

VL

L

M

H

VH

Criticality

E

Not Acceptable Redesign (MOC)

Not Acceptable Redesign (MOC)

Not Acceptable Redesign (MOC)

MTO List

6

H

Not Acceptable Redesign (MOC)

Not Acceptable Redesign (MOC)

Not Acceptable Redesign (MOC)

6

12

MH

Not Acceptable Redesign (MOC)

MTO List

MTO List

12

18

M

MTO List

6

6

18

No inspection

L

6

12

12

No inspection

No inspection

N

Review based on IOW excursions

No inspection

No inspection

No inspection

No inspection

Automated shear wave ultrasonic testing of 80 –100% of all weldments in the susceptible area and >25% of the affected surface in the remainder of the susceptible area, if there are no further welds in the main run pipe.

(Note 3 and 4)

Inspection of 80-100% of the susceptible areas by:

Visual inspection and

DPI or MPT for all relevant quill-nozzle welds.

(Note 4)

Manual UT angle beam or automated shear wave ultrasonic testing of 50 –79% of all weldments in the susceptible area and 20%-25% of the affected surface in the remainder of susceptible area, if there are no further welds in the main run pipe.

(Note 2, 3, and 4)

Inspection of 50-79% of the susceptible areas by:

Visual inspection and

DPI or MPT for all relevant quill-nozzle welds.

(Note 4)