IN-SITU METALLOGRAPHY OF HEATER MANILFOLD · 2019. 3. 22. · The manifold comprised of ASME SA335 P11 (1 ¼Cr, ½Mo) low alloy steel and had been in service for twenty years. Each

Steel Image Inc., Failure Analysis and Metallography 7 Innovation Drive, Suite 155, Flamborough Ontario, Canada, L9H 7H9, (289) 895-8363

IN-SITU METALLOGRAPHY OF HEATER MANILFOLD

EXAMPLE REPORT

Modified from Original Report

- Electronic Copy -

Shane Turcott, P.Eng, M.A.Sc. Principal Metallurgist

It broke. Understand why. Solve the problem. [email protected], (289) 895-8363

In-Situ Metallography of Heater Manifolds Page 1 of 9

IN-SITU METALLOGRAPHY OF HEATER MANILFOLDS

SUMMARY (Preliminary)

During shutdown inspection, in-situ metallography was conducted at several high stress sites along piping and heater manifolds. Included in this inspection were the weld toes of six manifolds. The manifold comprised of ASME SA335 P11 (1 ¼Cr, ½Mo) low alloy steel and had been in service for twenty years. Each site selected for evaluation had been prepared for in-situ metallography by grinding and then polishing to a 1µm finish. To increase the confidence in creep recognition, three 3% nital etch-polish iterations were completed. Replications were made in the as-polished and after final etching. Optical examination was completed on-site in order to provide results immediately. Of the twelve sites evaluated, two sites exhibited Stage 5 creep damage. Figures 1 and 2 display the locations of the two largest cracks present at the site evaluated on the Heater Cell A Outlet Manifold lug. Figures 3 through 5 display the creep crack features at this site including their intergranular morphology and surrounding creep voids. The cracks and adjacent creep voids were along the weld fusion line within the weld metal. The largest of the two cracks measured approximately 4mm in length. The formation of macro-cracks warranted the rating of Stage 5 creep (rating scale in Appendix B). Figure 6 displays the approximate location of the creep cracks present on the Heater Cell C Inlet Manifold lug. A series of three creep cracks had formed along the weld fusion line with a combined length of approximately 1.5mm (Figure 7). Intergranular creep voids had formed within the vicinity of the cracking. Creep damage was rated as Stage 5. Stage 5 creep cracks at the lugs would suggest that other portions/sites of Heater Cell A and C manifolds, which had similar or higher stresses during service, would also be at risk of having sustained creep damage.



Figure 1: Photographs displaying the Heater Cell A Outlet Manifold lug. Stage 5

creep cracks were found at the inside edge of the lug weld.



Figure 2: Photographs displaying creep cracks at the lug weld fusion line. Heater

Cell A Outlet Manifold lug.

Creep cracks

Weld Metal

Creep cracks at weld fusion line

Base Metal



Figure 3: Micrographs displaying the two largest creep cracks found at the weld interface/fusion

line of Heater Cell A Outlet Manifold lug. The cracks exhibited an intergranular morphology consistent with creep cracking. Based upon their size, these cracks would be rated at Stage 5 creep damage (rating chart in Appendix B). Images taken from replications, etched on-site using 3% nital.

a) Cell A, Outlet, Crack #1, ~100x, full etch

b) Crack #1, ~100x, light etch

c) Crack #2, ~75x, full etch

d) Crack #2, ~75, light etch

Weld Metal

HAZ

Weld Metal

HAZ



Figure 4: Micrographs displaying creep voids (black dots) at the edge of Crack #1 of

the Heater Cell A Outlet Manifold lug. Creep voids were observed along the length of the replicated weld fusion line. Images taken from replications, lightly etched on-site using 3% nital.

Creep voids

a) Crack #1, ~100x,

b) Crack Edge, 400x,



Figure 5: Micrographs displaying creep voids (black dots) at the edge of Crack #2 of

the Heater Cell A Outlet Manifold lug. Both the crack and creep voids were intergranular, classic for creep cracking. Images taken from replications, etched on-site using 3% nital.

a) Crack #2, ~75x,

b) Crack Edge, 400x,

Creep voids

Intergranular creep



Figure 6: Photographs displaying the Heater Cell C Inlet Manifold lug. Stage 5 creep

cracks were found at the weld.

Approximate location of creep

cracks



Figure 7: Micrographs displaying creep cracks at the weld two of Heater Cell C Inlet

Manifold lug. The cracks and adjacent voids exhibited an intergranular morphology consistent with creep cracking. Based upon their size, these cracks would be rated at Stage 5 creep damage (rating chart in Appendix B).

a) Cell C, Inlet, Crack , ~100x

Creep cracks

Creep crack

b) Crack Edge , 200x c) Adj Crack , 400x

d) Adj Crack , 1000x

Creep voids

Creep voids

Creep crack



APPENDIX A: LEVEL CLASSIFICATIONS OF SPHERIODIZATION

Spheroidization of carbon and alloy steels is a long-term degradation mode that occurs gradually over years and decades of service (depending upon the temperature of operation). Eventually spheroidization will result in strength reduction of the steel. Advanced Levels E-F spheroidization damage often precedes creep void/crack formation. The schematics below illustrate the six stages of spheroidization.

APPENDIX B: SUMMARY OF CREEP STAGES

Table B1: Creep Damage Stages

Stage Description Recommended Boiler

Remedial Actions* 1 No creep voids No action 2 Intermittent creep voids Re-inspect 3-5 years 3 Oriented, creep void strings Re-inspect 1-3 years 4 Microcracks Replace in 6 months 5 Macrocracks Replace immediately

Figure B1: Schematics displaying the different stages of creep void damage.

*These remedial recommendations are for boilers. They are included to provide a reference regarding the

severity of creep damage relative to their impact upon reliability. The concern of creep damage should be evaluated specific to each component/equipment design.

Stage 2 (isolated voids)

Stage 3 (void strings)

Stage 4 (microcracks)

Stage 5 (macrocracks)

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IN-SITU METALLOGRAPHY OF HEATER MANILFOLD · 2019. 3. 22. · The manifold comprised of ASME SA335 P11 (1 ¼Cr, ½Mo) low alloy steel and had been in service for twenty years. Each