[MODULE 2 PART 3] API 571 (3rd ED, Mar 2020) - API 570 STUDY GUIDE - AMINE STRESS CORROSION CRACKING

 

API 570 STUDY GUIDE 

MODULE 2 PART 3

AMINE STRESS CORROSION CRACKING

API 571 (3rd ED, Mar 2020)

Amine Stress Corrosion cracking 

or 

Amine SCC or Amine Cracking

Amine SCC is related to tensile stress, type of amine and temperature

Amine SCC causes CRACKS in Carbon Steels and Low-alloy steels. 

Click here for reading the previous blog in this series

5. Appearance or Morphology of Damage

All the points given in Clause 3.3.5 (a) to (g) has to be remembered. Each point can be asked as a question in the exam.

6. Prevention/Mitigation

1. Stress Relieving (For CS)

2. Water wash (For CS)

3. Using SS material, SS Clading or other corrosion resistant Alloys instead of CS

The recommended minimum stress-relief temperature is 635 ± 15 °C.

The stress relieving applies to repair welds, internal and external attachment welds.

Thoroughly water wash non-PWHT’d carbon steel piping and equipment prior to welding, heat treatment, or steam out.

7. Inspection and Monitoring

Amine SCC cracks initiate on the surface of piping and equipment. From this we can understand that any NDT method that can properly detect surface flaws can be used for this method.

The very common surface flaw detection method is Liquid Penetrant testing (PT). PT can be used for the detection of Amine SCC. But it should NOT be the only means of detection. That means some other surface flaw detection method also to be used on the same surface. PT may not be effective in finding tight cracks because the cracks are oxide filled.

Radiographic Testing (RT) - RT may not be effective in detecting fine, tight cracks.

Wet fluorescent magnetic particle testing (WFMT), Alternating current field measurement (ACFM) and Eddy current testing (ECT) are effective techniques. If these methods are used then there is a condition. Proper surface preparation by grit blasting, high-pressure water basting, flapper wheel abrasive grinding or other method is required to remove scale and contaminants depend on the techniques used for detection.

Angle beam ultrasonic techniques can be effective to detect and size cracks and would be the methods typically used for piping. SWUT and PAUT can also be used to periodically monitor crack growth.

Angle beam UT: shear wave ultrasonic testing (SWUT) and phased array ultrasonic testing (PAUT)

Caution must be exercised when interpreting results on piping welds that have not previously been inspected with angle beam UT (SWUT or PAUT) as it may be difficult to distinguish SCC from original fabrication flaws.

Acoustic emission testing (AET) can be used for locating cracks and monitoring crack growth.

Locate/detect crack, Crack size detection, Crack growth Monitoring: These three are to be studied without confusions.

Positive identification of amine cracking can be confirmed by metallographic analysis.

8. Related Mechanisms

The below stress corrosion cracking mechanisms are similar in appearance to Amine Stress Corrosion Cracking

1. Caustic Stress Corrosion Cracking (Will study in detail)

2. Carbonate Stress Corrosion Cracking

3. Ammonia Stress Corrosion Cracking

The related mechanisms are also to be remembered in the examination point of view.

Important Points

CS, LAS, Aqueous alkanolamine, stress, non-PWHT, Near Weld joints, Highly cold worked parts

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