API Publ 2207:1998 pdf download

API Publ 2207:1998 pdf download.Preparing Tank Bottoms for Hot Work.
3.2.5 Grounding leads from the welding machine should be attached directly to a bared surface on the tank shell on which hot work is to be performed. Welding leads should be carefully inspected for insulation abrasions, cuts, scuffs, or breaks; any of these can cause shorting.
3.2.6 Compressed-gas cylinders used far cutting operations should be securely fastened in an upright position and kept outside the tank at a safe distance from the open manholes. When not in use, cutting torches and hoses must be shut off at the cylinder valves and kept outside the tank. Cornpressed-gas supply hoses and hose connections should be inspected for leaks prior to being taken inside the tank.
To prevent a possible flammable mixture with air from forming in the tank. compressed-gas supply hoses must be protected from damage outside the tank and from bums. cuts, breaks, or other damage inside the tank.
3.2.7 While work is in progress, all work areas must be monitored for oxygen deficiency and combustible and toxic atmospheres.
4 Inspection Procedures
4.1 GENERAL PROCEDURES
The tank bottom must be inspected, when repairs are planned. regardless of its suspected condition.
4.2 SPECIFiC PROCEDURES
Appropriately sized small openings are sometimes made in the tank bottom by cold cutting or by drilling holes in each area where hot work is to be performed. These openings facilitate visual inspection and freeing the interior from gas. When such openings are made, care must he taken to avoid a source of ignition that could result in a lire or explosion arising from flammable vapors or liquid that might be released from under the tank bottom. A coolant should be applied to the cutting edge of tools to reduce friction heat. The use of open-type electric drilling machines is not recommended.
If tank-bottom-to-shell repairs are to be made, care must be taken to remove any exterior insulation on the bottom of the tank shell that could be oil soaked; hot work conducted internally could cause oil-soaked insulation to ignite. Before the insulation is removed, its type should he determined so that it can be removed property.
5.2 MINOR REPAIRS
Minor repairs usually involve welding corrosion pits and patches or other localized jobs. such as welding supports or braces. If the bottom is not in good condition, the following procedure may be used:
a. Drill and tap a hole for a 13 millimeter (‘, inch) pipe adjacent to the repair area.
h. Connect a supply of carbon dioxide or other inert ga.s to the 13 rnillimeter(’/2 inch) tap. using metal tubing. A pressure control valve with a flow indicator should be used to prevent ovcr-pressunng of the lank bottom.
c. Prior to beginning the hot work, establish a flow of inert gas under the tank bottom in the vicinity of any proposed welding to ensure that any flammable vapors have been swept away or diluted so that they cannot support combustion.
d. When using inert gas. continuously monitor the area to assure that the oxygen content remains between 19.5 and 22.5 percent.
e. When the welding has been finished in a localized area. stop the flow of inert gas, remove the tubing. plug the bole with a tapered pin or other device, and bark weld promptly before moving to another area.