API 570 EXAM STUDY GUIDE [MODULE 2 : PART 3] EROSION/EROSION-CORROSION

API 570 EXAM STUDY GUIDE

API 571 STUDY GUIDE


As discussed in API 570 STUDY GUIDE MODULE 2 : PART 2, the important points of each mechanism will be discussed here. You have to go through the relevant portion of the code for thorough understanding on the topic. 

4.2.14 of API 571 : Erosion/Erosion-Corrosion

There are two terms in this 1) Erosion 2) Erosion-Corrosion.

So there will be points in all the subheadings related to both these points. That means for example under the heading Prevention/Mitigation there will be points to prevent erosion and also there will be point to prevent corrosion and the related erosion.

Description of Damage

Erosion is  the mechanical removal of surface material. Metal is removed Mechanically and it is from the surface of the material.


For mechanical removal there should be something which should scratch the material from the surface and that is by the relative movement between or impact from solids, liquids or any combination thereof. Liquid and Vapor also causes erosion that means Liquid and vapor also scratches material from the surface.

Erosion-corrosion: suppose a protective film on a surface prevents corrosion of a surface. If that protective layer is removed by erosion then fresh material is exposed where corrosion may occur. This way erosion along with corrosion makes mechanical damage to the metal.

Affected Materials


All Metals, Alloys and Refractories


Critical Factors

The size, shape, density and hardness of the impacting medium affect the metal loss rate.

Those factors which may increase the corrosion will also increase the Erosion-Corrosion . So increase in temperature and pH etc that which increases the corrosion increase the erosion-corrosion also.

Affected Units

All types of equipments exposed to moving fluids and or catalyst

Ersoion can be caused by gas borne catalyst particles

Hydroprocessing reactor effluent piping may be subject to erosion-corrosion by ammonium bisulfide.

Apperance

The metal losses often exhibit a directional pattern.

Localized loss in thickness in the form of pits, grooves, gullies, waves, rounded holes and valleys.

Prevention/Mitigation

Erosion:-
Improvements in design (involve changes in shape, geometry and material selection)
Read the examples of design improvements under the clause 4.2.14.6 (a) of API 571

Increased Substrate hardness

Erosion-Corrosion:-
Corrosion resistant alloys
Altering the process environment to reduce corrosivity


Inspection and Monitoring

Visual Examination
RT/UT for detecting the extent of metal loss
IR scans can detect refractory loss on stream


Related Mechanism

Cavitation
Liquid impingement erosion
Fretting


EXAM TUTORIAL VIDEO


Questions and Answers

The questions and answers are for the evaluation of  your understanding on the subject. You have to read the relevant portion of the code for answering these questions.





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