How to monitor crack growth

AET – acoustic emission testing

Caustic Stress Corrosion Cracking (Caustic Embrittlement: AET can be used for monitoring crack growth and locating growing cracks.

Ammonia Stress Corrosion Cracking: For steel storage tanks and or piping in anhydrous ammonia WFMT welds inside tanks, External UT Shear wave inspection using TOFD, AET

Amine Stress Corrosion Cracking: AET can also be used for monitoring crack growth and locating growing cracks.

Wet H2S Damage (Blistering/HIC/SOHIC/SSC): AET can be used for monitoring crack growth.

Carbonate Stress Corrosion Cracking (ACSCC): AET can be used for monitoring crack growth and locating growing cracks.

High Temperature Hydrogen Attack (HTHA): AET is not a proven method for the detection of damage.

SWUT – shear wave ultrasonic testing

normal probe vs angle probe (eg 70 degree)

Two predominant types of waves, or wave modes, are generated within a material with ultrasonic waves: longitudinal and shear. Longitudinal waves (L-Waves) compress and decompress the material in the direction of motion, much like sound waves in air. Shear waves (S-Waves) vibrate particles at right angles compared to the motion of the ultrasonic wave. The velocity of shear waves through a material is approximately half that of the longitudinal waves. The angle in which the ultrasonic wave enters the material determines whether longitudinal, shear, or both waves are produced.

Anodic SCC vs Cathodic SCC

Stress corrosion cracking (SCC) is a brittle fracture caused by the combined action of tensile stress and corrosive environment Cracks induced by stress corrosion may be intergranular, transgranular or mixed (combining intergranular and transgranular morphology).

Sulfide stress cracking (SSC) is a form of hydrogen embrittlement which is a cathodic cracking mechanism. It should not be confused with the term stress corrosion cracking which is an anodic cracking mechanism.

Hydrogen assisted stress corrosion corrosion cracking is a separate type of SCC, which is principally different from the stress corrosion cracking undergoing by anodic dissolution.

In contrast to anodic dissolution mechanism Hydrogen assisted cracking is enhanced by cathodic reaction: H⁺ + e^- = H occurring on the crack tip surface The atomic hydrogen dissolves in the metal where its ions interact with the dislocations of the crystal lattice causing decrease of the metal ductility (hydrogen embrittlement).
Hydrogen cracking effect is increased in harder materials and at higher temperatures.

Hydrogen assisted corrosion cracking may be prevented by selection of suitable materials and maintaining the environment solution at neutral or basic PH (PH>6). In contrast to anodic stress corrosion hydrogen cracking is enhanced by Cathodic protection.

Alternating current field measurement

Alternating Current Field Measurement (ACFM) is an electromagnetic technique for non-destructive testing detection and sizing of surface breaking cracks. It was derived from the methods used in eddy-current testing and works on all metals, ferrous or non-ferrous. Since it doesn't require direct electrical contact with the surface it can work through coatings such as paint or rust.

ASME B31.3 -2008- fluid service

fluid service: a general term concerning the application of a piping system, considering the combination of fluid properties, operating conditions, and other factors that establish the basis for design of the piping system. See Appendix M.

(a) Category D Fluid Service: a fluid service in which all the following apply:

(1) the fluid handled is nonflammable, nontoxic, and not damaging to human tissues as defined in

para. 300.2

(2) the design gage pressure does not exceed 1035 kPa (150 psi)

(3) the design temperature is from −29°C (−20°F) through 186°C (366°F)

(b) Category M Fluid Service: a fluid service in which the potential for personnel exposure is judged to be significant and in which a single exposure to a very small quantity of a toxic fluid, caused by leakage, can produce serious irreversible harm to persons on breathing or bodily contact, even when prompt restorative measures are taken

(c) High Pressure Fluid Service: a fluid service for which the owner specifies the use of Chapter IX for

piping design and construction; see also para. K300

(d) Normal Fluid Service: a fluid service pertaining to most piping covered by this Code, i.e., not subject to the rules for Category D, Category M, or High Pressure Fluid Service