API 653:2001 pdf download

API 653:2001 pdf download.Tank Inspection, Repair, Alteration, and Reconstruction.
4.3.8 Shell Welds
The condition of the tank shell welds shall be eiluated for suitability for service. Any deterioration of the existing welds that results from corrosion or pitting must be eiluated and appropriate repair procedures established or the tank rerated as necesstiry. Some typical shell butt-weld flaws and recommended procedures for repairs ate given in 9.6.
4.3.9 Shell Penetrations
4.3.9.1 The condition and details of existing shell penetrations (nozzles, manways. cleanout openings, etc.) shall be reviewed when assessing the integrity of an existing tank shell. Details such as type and extent of reinforcement, weld spacing, and thickness of components (reinforcing plate, nozzle neck, bolting flange, and cover plate), are important considerations and shall be reviewed for structural adequacy and compliance with the applicable standard. Any noncompliance, or deteñoration due to corrosion, must be assessed and repair procedures established where appropriate or the tank remted. as necessary.
4.3.9.2 Nozzle wall thickness shall be etluated for pressure and all other loads,
4.4 TANK BOTTOM EVALUATION
4.4.1 General
Tank bottom inspection strategies shall provide suitable data which, when used with the procedures in this standard. will determine the tank bottom integrity necessaiy to prevent leakage of fluids that may cause environmental damage. Each aspect of corrosion phenomena, and other potential leak or failure mechanism must be examined. Periodic assessment of tank bottom integrity shall be performed in addition to the internal inspections specified in 6.4. The assessment period shall be less than or equal to the appropriate internal inspection interval given in 6.4.2 or 6.4.3. The use of leak detection tests or monitoring systems (such as double bottoms or liners under tank bottoms with leak detection pipes) will satisf’ the requirement for periodic assessment between internal inspections.
Excessive foundation settlement of slorage tanks can affect the integrity of tank shells and bottoms. Therefore, monitoring the settlement behavior of tanks is a recognized practice to assess the integnty of tank bottoms. Refer to Appendix H for techniques for evaluating tank bottom settlement.
4.4.2 Causes of Bottom Failure
The following list gives me historical causes of tank bottom leakage or failure that shall be considered in the decision to line, repair, or replace a tank bottom:
a. internal pining and pining tates in the anticipated service. b. Corrosion of weld joints (weld and heat affected zone).
c. Weld joint cracking history.
d. Stresses placed on the bottom plates by roof support loads and shell settlement.
e. Underside corrosion (normally in the form of pitting).
f. Inadequate drainage resulting in surface water flowing under the tank bottom.
g. The lack of an annular plate ring when required.
h. Uneven settlement that results in high localized stresses in the bottom plates.
i. Roof support columns or other supports welded to the tank bottom where adequate allowance for movement was not made.
j. Rock or gravel foundation pads with inadequately filled-in surface voids.
k. Nonbomogeneous fill under the tank bottom (for example. a lump of clay in a sand foundation pad).
l. Inadequately supported sumps.
4.4.3 CathodIc Protection of Tank Bottoms
A selection basis flr cathodic protection systems for the underside of tank bottoms is covered by API RP 651.