3.14 Caustic Corrosion

Question 1

Localized corrosion due to the concentration of caustic (alkaline) solutions such as_______________. usually occurs under evaporative or high heat transfer conditions
(commonly called caustic gouging). Also, corrosion resulting in general thinning can occur at elevated temperatures, depending on _____________________

Answer 1

NaOH and KOH ; alkali or caustic solution strength.

Question 2

Affected Materials are:

Answer 2

Primarily carbon steel, low-alloy steels, and 400 series SS. 300 series SS can also be susceptible to caustic corrosion and caustic SCC at elevated temperatures. (160 °F a 210 °F (70 °C a 100 °C)

Question 3

A Critical Factors is the presence of Caustic (NaOH or KOH) usually added to _________, _____________ or_______________, may also enter process streams through leaks in condensers or other process equipment.

Answer 3

BFW, process for acid neutralization or remove sulfur or chlorides

Question 4

caustic gouging is most often associated with

Answer 4

• boilers and steam-generating equipmentcluding heat exchangers.
• Crude unit feed commonly preheat exchangers, furnace tubes, and transfer lines.
• Units that use caustic for removing sulfur.
• Heat-traced tanks used for caustic storage and caustic feed equipment

Question 5

A critical factor In high-solution-strength caustic are temperatures above about ________

Answer 5

170 °F (75 °C).

Question 6

A critical factor for localized caustic gouging to occur, a _______________ must exist to build up the caustic strength or salt concentration.

.

Answer 6

concentrating mechanism

Question 7

Others factos as Contaminants (chlorides and hypochlorites) and Heat tracing contribute to

Answer 7

increase the corrosivity of caustic solutions.

Question 8

Critical factors are:

Answer 8

1. Presence of Caustic (NaOH or KOH).
2. Temperatures above 170 °F (75 °C).
3. A concentrating mechanism.
4. Contaminants (Chlorides and hypochlorites).
5. Heat tracing.

Question 9

Caustic gouging is typically characterized by _______________ that may appear as __________ in a boiler tube or locally thinned areas under insulating deposits.

Answer 9

Localized metal loss ; grooves

Question 10

Localized gouging may result along a waterline where corrosives concentrate. In vertical tubes, this may appear as a __________________ ; On the other hand In horizontal or sloped tubes, grooving may appear at the top of the tube or as _____________ on opposite sides of the tube.

Answer 10

circumferential groove; longitudinal grooves

Question 11

Corrosion of CS in high-concentration caustic at elevated temperatures will be ___________ but likely confined to the location of the high temperature, e.g. _______________

Answer 11

generalized ; next to heat tracing.

Question 12

Caustic corrosion is best prevented through ______________. Also the Damage can be minimized by __________________ of free caustic

Answer 12

Proper design ; reducing the amount

Question 13

CS a SS have serious corrosion problems in high-strength caustic solutions at
elevated temperatures. ________ and ___________

Answer 13

A

Question 14

For General Corrosion _____________ techniques can measure general loss.

Answer 14

UT using a straight beam or UT scanning

Question 15

For Localized Corrosion ________, ________, _______, may be necessary to determine the extent of localized corrosion. ______ has also been used within the limits of the technique.

Answer 15

UT, PAUT, TOFD ; RT

Question 16

Heat or steam tracing can cause _________________ at the point of contact due to locally high temperatures or improper installation. This is an area to focus on for inspection.

Answer 16

localized corrosion

Question 17

Caustic injection sites should be examined and monitored as discussed in _____ and _____

Answer 17

API 570 and API 574.

Question 18

When internal access is not available (e.g. steam equipment, tubing, small-diameter equipment, or equipment with ports), VT may be performed

Answer 18

using a boroscope