API 653 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

API 653 scope pressure limit

API 653 covers aboveground steel storage tanks built to API 650 or API 12C whose internal design pressure does not exceed 2.5 psig (17 kPa gauge).

One-foot method formula

Shell thickness t = 2.6D(H-1)G/(SE) in US customary units, where D is tank diameter in ft, H is design liquid height in ft, G is specific gravity, S allowable stress, E joint efficiency.

Joint efficiency values

For shell butt joints, E is 1.00 with full radiography, 0.85 with spot radiography, and 0.70 with no radiography; E appears directly in the shell thickness formula.

Minimum shell plate thickness

API 650 requires new shell plates to be at least 3/16 in. (5 mm) nominal thick, exclusive of corrosion allowance, regardless of the calculated design thickness.

Emergency venting purpose

Emergency vents, sized per API 2000, relieve pressure from fire exposure or abnormal vapor generation beyond normal vent capacity, protecting the shell-to-roof joint.

Frangible roof design

A roof-to-shell attachment intentionally weaker than the shell-to-bottom connection, so excessive internal pressure lifts the roof and vents the tank before the shell is damaged.

Seismic design appendix

API 650 Appendix E requires evaluation of impulsive and convective liquid motion, shell compressive stress, sloshing wave height, and anchorage against overturning for tanks in seismic areas.

External inspection interval

API 653 requires in-service external inspections by an authorized inspector at intervals not exceeding 5 years, or more often where corrosion rates or conditions warrant.

Internal inspection interval

Internal inspection intervals shall not exceed 20 years and shall not exceed one-half of the estimated remaining corrosion life of the shell or bottom.

Corrosion rate calculation

Corrosion rate equals thickness lost between two measurement dates divided by the elapsed time; remaining life equals current thickness minus minimum required thickness divided by that rate.

Hydrostatic test hold

A new or reconstructed tank is filled with water and held, typically 24 hours, before all welded joints are visually examined and shell settlement is measured.

Tank bottom MFL scan

Magnetic flux leakage scanning detects bottom plate thinning and pitting over large areas quickly; findings are then confirmed with ultrasonic thickness measurements at grid points.

Fitness-for-service assessment

Corrosion, cracks, or flaws found during inspection may be evaluated with API 579-1/ASME FFS-1 to decide whether the tank is fit for continued service.

Inspector vision requirement

Inspectors must have near vision corrected to Jaeger 1 at 12 in. and color vision sufficient to distinguish the colors used in the examination method.

Repair definition

Any work necessary to restore a tank, or part of a tank, to a condition suitable for continued service without changing the tank's structural configuration.

Alteration definition

Work that changes a tank's structural configuration or design, such as changing shell height, adding an opening larger than 12 in. nominal pipe size, or changing the foundation.

Reconstruction definition

Reassembly of a tank that has been dismantled and relocated; the tank must then satisfy applicable new-construction requirements, including testing and nameplate data.

Insert plate requirements

Shell insert plates shall be at least 12 in. (300 mm) wide, have rounded corners, and be at least as thick as the minimum thickness required at that location.

Welding qualification requirement

All repair, alteration, and reconstruction welding must use welding procedures and welders qualified under ASME Boiler and Pressure Vessel Code Section IX.

Post-repair hydrostatic test

Major repairs and alterations, such as shell plate replacement or new large openings, require hydrostatic testing; the authorized inspector may waive it for minor repairs where impractical.

Tank entry oxygen range

Before confined-space entry, oxygen must be tested and maintained between 19.5 and 23.5 percent by volume, with flammable vapor and toxic gas also within acceptable limits.

Hot work gas limit

Hot work on or in a tank requires a permit and a combustible gas reading below 10 percent of the lower explosive limit, with continuous monitoring while work proceeds.

Static fill rate limit

To control static ignition, initial filling is limited to about 3 ft/s (1 m/s) until the inlet is submerged, after which higher filling rates are permitted.

Cathodic protection criterion

Steel tank bottoms in soil are adequately protected when polarized to at least -0.85 V measured against a copper-copper sulfate reference electrode.

Overfill protection standard

API 2350 sets overfill prevention requirements including level alarms, independent high-high detection, and procedures to stop filling a tank before it overflows.

Water bottoms control

Water and sediment accumulating on the tank bottom promote pitting and underside corrosion; routine water draw-off and sludge removal reduce the corrosion rate.

Out-of-service isolation

Tanks removed from service must be cleaned, gas-freed, and positively isolated from all connected piping, typically with blinds or a double block and bleed arrangement.

Return-to-service inspection

Before an out-of-service tank returns to service, an authorized inspector evaluates its condition and specifies any required internal or external inspection and testing.

Relocation treated as reconstruction

A dismantled and re-erected tank is a reconstruction, so it must comply with new-construction requirements for foundation, shell roundness, welding, and hydrostatic testing.

Nameplate after relocation

The tank keeps its original nameplate; reconstruction and relocation data are recorded on a new or supplemental nameplate attached near the original.

Record retention period

Construction, inspection, repair, and alteration records must be maintained by the owner for the life of the tank and made available to the authorized inspector.

Inspection record contents

Records include thickness measurements with locations and dates, calculated corrosion rates and remaining life, examination and test reports, and nameplate data.