Sulfuric Acid / Sulfur Storage Tank Inspections

AIChE Central Florida AnnualAIChE Central Florida Annual Convention

Sulfuric Acid WorkshoppJune 12, 2009

JWD

Typical Causes of CorrosionTypical Causes of Corrosion

• Material defectsMaterial defects• Weld – heat affected zone

W ld hi h it• Weld – high porosity • Weld – lack of full penetration• Hydrogen grooving

Tank Protection MethodsTank Protection Methods

• Maintain low acid storage temperatureMaintain low acid storage temperature• Anodic protections systems

C ti• Coatings• S.S. nozzle liners• Painting (external)• Routine Inspection & MaintenanceRoutine Inspection & Maintenance• Life Expectancy: 15-25 years

Inspection TopicsInspection Topics

• Inspection frequency – API Code (?)Inspection frequency API Code (?)• Full internal inspection:

Cl i l i ti (“ h d ” t h i )– Close visual inspection (“shadow” technique)– Vacuum check all welds

• External thickness checks:– Target the “T” weld areas– As close to welds as possible

• Destructive v. Non-Destructive

Sulfuric Acid Tank – Shell WallSulfuric Acid Tank Shell Wall

Heat Affected Zone CorrosionHeat Affected Zone Corrosion

Heat Affected Zone Corrosion

Material Defect – Shell Wall

Material Defect – Floor Plate

Shell Plate – Material Defect

Material Defect – Shell Wall

Material Defect - < 1-year

Corrosion Undercut of Weld Seam

Weld Undercut

Corrosion Along Weld Seam

Weld Porosity DefectsWeld Porosity Defects

Weld Porosity Defects

Weld Porosity Defects

Weld Porosity Defect

Weld Porosity Defects

Weld Porosity

Destructive Testing – Material Defect

Reverse Side – Same HoleReverse Side Same Hole

Coated v. Non-Coated

Thickness Check the Weld “T”Thickness Check the Weld T

Sulfur TanksSulfur Tanks

• Internal heating coils introduce moisture sourceInternal heating coils introduce moisture source– Permanently mounted on floor or shell– Hanging style removable for repair/replacementg g y p p– External style removes moisture from the equation

• External Insulation– Missing insulation can result in cold spots and solid g p

sulfur formation against tank walls.

External Inspection

Internal Inspection

New Tank Fabrication

Internal Shell Wall & Floor

Formation of Pyrophoric Iron SulfidesFormation of Pyrophoric Iron Sulfides• Hydrogen Sulfide – H2S

M i H O• Moisture – H2O• In presence of Iron (Fe) produces Iron

Sulfide (FeS) and Iron Oxide (Fe2O3) in an autocatalytic reaction.

• The iron sulfide formed under anaerobic conditions can react in a highly exothermic g yreaction when exposed to oxygen resulting in a fire or explosion hazard.p

Sulfur Tank Roof Internal Corrosion

Sulfur Tank Roof CorrosionSulfur Tank Roof Corrosion

Internally Mounted Coils

Hanging Removable CoilsHanging Removable Coils

Externally Mounted Coils