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DAILY POINTS TO RECALL (DAY 9)

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1. Vessel inspections are for the safety, continuity, reliability.2. Graphitization in Carbon Steels takes place due to prolonged

exposure in 825 to 1400 deg. F range resulting in decompositionof Steel into Ferrite Crystals and Graphite Nodules. In-situ

metallography is used to detect the Graphitization

3. External inspection of Pressure Vessels and Exchangers shouldstart with ladders, platforms, stairways connected to or bearing onvessel.

4. External surfaces of vessels shall be examined for not only forcorrosion but also for leaks, cracks, buckles, etc.

5. If any settling is seen on vessel, nozzles and adjacent shell areashall be inspected for distortion and cracking.

6.

Hammer test shall be followed by suitable NDT.7. Grounding connection resistance shall not exceed 25 ohms but 5

ohms is normally preferred.

8. In presence of acidic corrodents (PH < 7) hydrogen blistering isexpected above and below (close to) liquid level.

9. Auxiliary equipments (Pressure gauges, sight glass, safety valvesetc. may be visually inspected while in service. Undue vibrationsshall be arrested by providing additional supports or qualifiedengineer should determine if these could lead to fatigue failure.

10. First step for internal inspection is review of previous records.11. For heavy wall vessels at high pressure, major concern is crack

damage particularly at the welds (Weld & HAZ).

12. Laminations run slant while cracks run normal to surface.13. Spark testing is effective method for breaks/leaks in paint, glass,

plastic and rubber lining.

14. UT is the primary means of obtaining thickness measurements.Other methods like profile radiography, Step-wedge comparison

radiographs, Corrosion buttons, test holes and depth drilling are

some other methods.15. Tamper embrittlement of chromium steel occurs due to loss of

ductility due to prolonged exposure to high temperature above650oF. It can be controlled by limiting "J" factor for base metals

and "X" factor for weld metals.

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16. All fatigue failure take place due to initiation of surface crack andpropagation of crack due to stress fluctuation. There are 3-typesof fatigue failures.

If surface cracks are due to stress concentration, weld undercuts,notches etc and stress fluctuation due to mechanical reasons

(vibrations, water hammer etc.) then it is Mechanical Fatigue. Ifstress fluctuation is due to temperature swing, it is Thermal

Fatigue. If initial surface cracks are due to corrosion, pitting etc.,it is Corrosion Fatigue.

17. Corrosion Erosion is due to combined action of corrosion anderosion. It can be reduced by controlling corrosion (by coating orusing corrosion resistant materials) and by controlling erosion (by

controlling flow velocity, providing harder surface).

18. Caustic embrittlement occurs due to combined action of highcaustic strength and higher temperature. It can be controlled bycarrying out PWHT and upgrading materials by Nickel alloys.

19. Sulphidation occurs due to sulpher or H2S content in the fluidhandled. It can be reduced by using Chromium containing steelsas construction materials.

20. Hydrogen blistering takes place due to migration of Hydrogenitems in the steel vessel walls. Hydrogen induced cracking (HIC)takes place if several Hydrogen blisters join together in the

material.

21. Stress assisted HIC (SAHIC) takes place due to propogation of HICcracks under effect of applied stress. Crack propagatesperpendicular to stress direction.

22. High temperature Hydrogen Attack (HTHA) is due to migration ofHydrogen atoms in the carbon steels which combines with carbonin carbons steel at high temperature to form Methane gas (CH4)

which collects at grain boundaries causing internal cracks. It canbe reduced by selecting the construction materials according toNelsen Curves. (The material should be above the point oftemperature and Hydrogen pressure).