API 653:2001 pdf download
API 653:2001 pdf download.Tank Inspection, Repair,Alteration,and Reconstruction.
b. For the maximum shear in net section of rivet, use 16,000lbfin.2
c. For the maximum bearing stress on plates or rivets，use32,000 lbf/in.2 for rivets in single shear, and 35,000 lbf/in.2for rivets in double shear.
4.3.4.3 For tanks with riveted joints, consideration shall begiven to whether,and to what extent,corrosion affects suchjoints. If calculations show that excess thickness exists, thisexcess may be taken as corrosion allowance.
4.3.4.4 Non-liquid loads (see 4.3.3.4) shall also be consid-ered in the analysis of riveted tanks.
4.3.5 Distortions
4.3.5.1 Shell distortions include out-of-roundness, buckledareas, flat spots,and peaking and banding at welded joints.4.3.5.2Shell distortions can be caused by many conditionssuch as foundation settlement, over- or under-pressuring, highwind,poor shell fabrication,or repair techniques,and soforth.
4.3.5.3Shell distortions shall be evaluated on an individualbasis to determine if specific conditions are consideredacceptable for continuing tank service and/or the extent ofcorrective action.
4.3.6Flaws
Flaws such as cracks or laminations shall be thoroughlyexamined and evaluated to determine their nature and extentand need for repair. If a repair is needed, a repair procedureshall be developed and implemented. The requirement forrepairing scars such as arc strikes, gouges, or tears from tem-porary attachment welds must be evaluated on a case-by-casebasis.Cracks in the shell-to-bottom weld are critical and shallbe removed and the weld repaired.
4.3.7Wind Girders and Shell Stiffeners
The evaluation of an existing tank shell for suitability forservice must also consider the details and condition of any
wind girders or shell stiffeners.Degradation by corrosion ofthese structural elements or their attachment welds to theshell may render these elements inadequate for the designconditions.
Excessive foundation settlement of storage tanks can affectthe integrity of tank shells and bottoms.Therefore,monitor-ing the settlement behavior of tanks is a recognized practiceto assess the integrity of tank bottoms. Refer to Appendix Bfor techniques for evaluating tank bottom settlement.
4.4.2Causes of Bottom Failure
The following list gives some historical causes of tank bot-tom leakage or failure that shall be considered in the decisionto line, repair, or replace a tank bottom:
a. Internal pitting and pitting rates 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 loadsand shell settlement.
e. Underside corrosion (normally in the form of pitting).
f. Inadequate drainage resulting in surface water flowingunder the tank bottom.
g. The lack of an annular plate ring when required.
h. Uneven settlement that results in high localized stresses inthe bottom plates.
i. Roof support columns or other supports welded to the tankbottom where adequate allowance for movement was notmade.
j.Rock or gravel foundation pads with inadequately filled-insurface voids.
k. Nonhomogeneous fill under the tank bottom (for example,a lump of clay in a sand foundation pad).
l. Inadequately supported sumps.
4.4.3Cathodic Protection of Tank Bottoms
Aselection basis for cathodic protection systems for theunderside of tank bottoms is covered by API RP 651.
4.4.4Internal Lining Protection of Tank BottomsApplied linings for intermal surfaces of tank bottoms arecovered by API RP 652.
4.4.5 Bottom Leak Detection
lf a tank bottom is to be replaced,consideration should begiven to installing a leak detection (tell-tale) system that willchannel any leak in the bottom to a location where it can bereadily observed from the outside of the tank.
