Section 9 — Storage Tanks

Welding Requirements for Atmospheric Storage Tanks

IPE Engineering Practice IPE-EP-9-1-2

Document number: IPE-EP-9-1-2 · Section: 9 — Storage Tanks

SCOPE

• This Practice covers requirements for weld procedure qualifications, weld process restrictions, and fabrication details used in the assembly of atmospheric storage tanks constructed to APl 650 or repair and reconstruction according to API 653.
• Any deviation to this Practice must be approved by the procedure described in EP 1-1-3.
• An asterisk (*) indicates that a decision by the Owner's Engineer or Owner is required, or that additional information is furnished by the Purchaser.
• A revision bar indicates all changes made to this Revision.

2.0 REFERENCES

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

DEFINITIONS

• Aggressive Environmental Service (AES) - Process services which result in material degradation such as cracking, scaling, blistering, and severe pitting and/or corrosion. Examples of such services are hydrogen service, wet hydrogen sulfide, cyanides, caustic, amine, and hydrofluoric acid. AES process fluid are defined in EP 10-2-1.
• Contractor - Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.
• Inspector - A Inflection Point Engineering, LLC appointed engineer or inspector.
• Manufacturer - The recipient of a direct or indirect purchase order for materials and/or equipment. In this context, a direct order is one issued to a manufacturer by a contractor or the Owner. An indirect order is one issued to a manufacturer by a vendor (recipient of a direct order) for materials, fabricated components, or subassemblies.

• Owner – Inflection Point Engineering, LLC
• Owner's Engineer - A Inflection Point Engineering, LLC appointed engineer.
• Purchaser - The party placing a direct purchase order. The purchaser is the Owner's designated representative.
• Purchase Order - The contractual document given to the Manufacturer to authorize a purchase.

GENERAL

• This Engineerng Practice shall be a mandatory supplement to other applicable IPE Engineering Practices where it is referenced.
• Conflicts between this and other engineering practices or fabrication codes shall be brought to the attention of the Owner and submitted in writing for review and decision.
• Compliance with this Practice does not relieve the Manufacturer from meeting the requirements of all governmental regulations or standard codes of practice.
• For field fabricated tanks, weather shields shall be used in inclement weather to protect the weld area from moisture and wind. The need for and suitability of the weather shields is subject to the discretion of the Inspector.

WELDING PROCEDURE REQUIREMENTS

• Welding Procedure Specifications shall conform to the requirements of Section IX of the ASME Code and to the additional requirements of this Practice.
• (*)Prior to any welding, one copy of each Welding Procedure Specification (WPS) along with the supporting Procedure Qualification Records (PQR) shall be submitted for written approval by the Owner's Engineer.
• Each WPS shall be specified on a weld map (line sketch) detailing where each welding procedure specification will be used. An alternate method of specification is location of the WPS on the actual fabrication drawings at each weld joint.
• Submitted welding procedures shall reference both the item name and the Purchase Order Number.
• (*)The use of any welding procedure without prior written approval of the Owner's Engineer shall result in rejection and removal of all deposited welds in question at the contractor's expense.

WELDING PROCESS REQUIREMENTS

• Oxyacetylene (OAW) or other oxy-fuel welding processes are not acceptable.
• (*)For field fabrication, approved welding processes shall be limited to shielded metal arc (SMAW), submerged arc (SAW) or a combination of the two. Other processes may be used if a written request is made to the Owner's Engineer prior to fabrication and is approved.
• SMAW shall be meet the following:
• Electrodes for SMAW welding of tanks are specified in Table 1.

• Electrodes of 3/16-inch diameter or less may be used for "all position" welding.
• Electrodes of ¼-inch diameter or less may be used for welds in the flat or horizontal positions.
• Group number F-1 electrodes shall not be used for single pass fillet welds.
• SAW shall meet the following:
• Electrode-flux combination shall meet the F7A2-EXXX classification.
• High manganese (EH-14) or carbon-Moly (EA1, EA2) electrodes are not acceptable.
• All multipass welds shall use a neutral flux.
• The use of recrushed SAW slag as a flux or flux addition is not permitted.
• (*)Shop fabrication of tank components may use welding processes other than SAW or SMAW if the proper WPS/PQR procedure documents have been submitted and approved by the Owner's Engineer.

WELDER PERFORMANCE QUALIFICATIONS

• All welders and welding operators shall be qualified by the bend test or radiographic method in accordance with Section IX of the ASME Code. The transfer of performance qualifications from one employer to another is not acceptable.
• The Inspector reserves the right to have any welder or welding operator retested at any time he feels the welders abilities are questionable.
• All welder and welding operator performance qualification records shall be made available to the Inspector upon request.
• The Inspector shall be permitted access to witness any welder or welding operator qualification tests.
• The Inspector has the authority to reject a welder or welding operator based upon visual inspection of the welder's test either during qualification or after completion.
• The following are additional requirements to be applied to all "Field Welding" or "On Site" welding contractors at the Owner's facility.
• (*)Welders shall be qualified in all positions before they are permitted to weld on field fabrications. Limited position qualifications for a specific job will be permitted only with written approval of the Owner's Engineer.
• Pipe butt weld qualifications are required for welders who make groove welds on nozzles that are NPS 24 in diameter or smaller.
• The Contractor shall furnish all materials, test equipment, a testing area and services necessary to prepare and test qualification coupons on site.
• Any welder or welding operator who fails a weld qualification test has the following retest options for that particular base metal/weld process combination:
• He may retest after a waiting period of 90 days, or

• He may obtain further training from an outside source until he successfully passes a test of similar material and position. He must then present documented proof of this training and testing before he will be permitted to retest.
• He may take an immediate retest consisting of two consecutive weld test coupons, both of which shall pass all required tests.

PRODUCTION WELDING REQUIREMENTS

• Preheat
• The minimum base metal temperature shall be 33°F prior to any welding unless required otherwise by the welding procedure specification. This also applies to tack welds, temporary attachments and thermal gouging.
• If the base metal temperature is 32°F or below, it shall be heated to approximately 100°F; or to a higher temperature, if required by the welding procedure specification, prior to the start of welding.
• Whenever material is wet or contains surface moisture or condensate, the weld area shall be dried by heating.
• For shell plates greater than 1 inch and up to 1.5 inches, the minimum required preheat shall be 100°F or higher if the higher temperature is specified on the WPS.
• Preheat shall be applied 3 inches in all directions from the point of welding and maintained throughout welding.
• Filler Metal
• All low hydrogen type electrodes shall be stored in their original sealed container. Once the sealed container is opened, they shall be placed in an electrode holding oven kept at a minimum temperature of 250°F.
• All SAW wire and flux shall be kept in a dry storage area.
• (*)For dissimilar joints between ferritic and austenitic base materials, the filler material shall meet the requirements of ASME classification E-NiCrFe-2 (Inco A), except that E-NiCrFe-3 (Inco 182), or E-309L may be used with written approval from the Owner's Engineer.
• Welder Identification
• Production Quality Control shall include welder identification of fabricated joints by either written documentation or stamping of the joints.
• A complete weld map showing the welder's identification symbols and corresponding weld joint numbers is an acceptable alternative to weld stamping.
• Requirements for stamping:
• Each welder shall be assigned a symbol and shall identify each joint he welds by stamping his symbol adjacent to the weld. Circumferential shell joints shall be stamped at approximately 10- foot intervals.
• Only 1/4 or 3/8-inch low stress steel stencils shall be used.

• Welder identification shall be stamped approximately 1 inch away from the weld. If more than one welder completes a joint, stamps shall move outward from the weld in chronological order, the welder completing the weld stamping his identification furthest away.
• Any weld not so identified shall either be removed, 100% radiographically examined (RT) or 100% ultrasonically examined (UT), at the Contractor's expense for acceptance at the discretion of the Inspector.
• Stamping is not required for fillet welded joints.
• Tank Shell Joints
• Horizontal and vertical shell butt joints shall be full penetration welds.
• All full penetration joints welded from two sides shall be backgouged or background to clean metal. Horizontal shell joints in plate 1/4 inch thick or less may be double SAW without backgouging provided all intermediate stops are ground out.
• (*)The shell to bottom/annular plate weld joint shall be made using the SMAW and/or SAW process and the same filler metal as required for the shell unless alternate weld procedure specifications were submitted and approved per paragraph 5.0. The shell to bottom/annular plate weld shall be made with a minimum of two weld layers. The second weld layer shall completely cover the first.
• All temporary attachments shall be welded using approved procedures and welders. Upon removal, any gouges shall be repaired by welding or blend grinding. After repair, the area shall be examined by either the liquid penetrant or magnetic particle method.
• Single or multi-pass vertical shell welds made using the automatic flux core (Verticore) or similar process are not acceptable unless all of the following restrictions are met.
• Use of this process shall not be part of the basis for a fabricators bid proposal. Use of this process may be offered as an alternative only, not as part of a firm bid for tank construction.
• (*)Written approval of the Owner's Engineer is required prior to the start of fabrication.
• The Lowest One Day Mean Temperature (LODMT) per EP 9-1-1 at the tank fabrication site shall be 10°F or higher.
• Base metal for the tank shell shall be listed in material Group III, IIIA, or V as specified in API 650.
• Prior to fabrication, sample test welds shall be done on the maximum and minimum base metal thickness where the process will be used. Heat input (Volts, Amps, and Travel Speed) shall be recorded on these tests and shall define the extreme values of the heat input range permitted in fabrication of the tank.
• Charpy Vee Notch (Cv) specimens shall be prepared from both the Sample Test Welds and Production Test Plates required. The Cv specimens shall be from the transverse direction. A set of three specimens shall be taken from each of the following locations:
• Weld Centerline
• Fusion line between weld and plate
• Heat affected zone (2 to 5 mm from fusion line)

• Base metal
• Charpy tests for the Group III and IIIA materials shall meet a 13 average/10 minimum foot pound value tested at the LODMT per API 650 for that tank site. Charpy tests for the Group V materials shall meet a 20 average/15 minimum foot pound value tested at the LODMT.
• Two side bend tests, dimensions per ASME Section IX, and a weld metal cross section macro etch sample shall be taken from each sample test weld and submitted for review.
• Production test plates shall be welded as part of the fabrication of each tank. Three test plates are required for tanks 200 feet or larger in diameter, two test plates for tanks 100 feet up to 200 feet, and one plate for tanks less than 100 feet. One test shall be from the bottom shell ring and no shell ring shall have more than one test. Charpy specimens shall be removed from these plates, shall be tested to the same extent as the Sample Test Welds, and shall meet the same minimum requirements.
• All weld seams shall be visually examined both inside and out for proper fusion of the weld to plate along the entire weld seam.
• All weld start locations in the bottom shell ring shall be given a through wall examination using either angle beam UT, radiography, or a combination of the two to assure complete fusion of the weld start.
• Annular Plate and Tank Bottom Welds
• Annular plates shall be joined together by full penetration welds using double welded butt joints with backgouging, groove welds with backing strips, or a combination of the two. All backgouging shall be inspected by the magnetic particle or dye penetrant method.
• All bottom plate to annular plate fillet welds shall be two pass minimum welds.
• When EP 9-1-1 requires a minimum joint efficiency for fillet welded bottom plates, the following procedure tests shall be made in addition to the requirements of ASME Section IX:
• A fillet lap weld, 18 inch minimum length, shall be made following the proposed welding procedure specification, including use of the same manufacturer's electrode type and size, same thickness and same material plate designation.
• The two ends of the test plate weld shall be cropped (approximately 2 inches) and discarded.
• The remaining sample shall be cut into 3 approximately equal pieces; then each of them cut again to obtain a 3 inch wide tensile specimen and a second piece for visual inspection.
• The minimum breaking tensile load of each of the 3 inch lap welds shall be 70 or 80% (as required by EP 9-1-1) of the minimum specified base metal strength.
• The three samples for visual inspection shall be polished and etched to show the weld penetration into the base metal.
• Complete penetration at the root of the fillet, penetration into both lap welded plates, and complete fusion of the cross section is required.

POST WELD HEAT TREATMENT (PWHT) - API 650

• PWHT shall be in compliance with API 650 and the requirements of this Practice.
• For the PWHT cycle, the minimum holding time at temperature shall be 1 hour for any tank that is up to and including one inch thick. The holding time at temperature for all vessels greater than 1 inch thick shall be 1 hour for each inch or fraction of an inch; for example 1-1/2 inch thick plate shall have a holding time of 2 hours.
• Corrosion allowance shall be included in material thickness when calculating minimum hold times.
• All tanks or tank components post weld heat treated off site shall be marked in accordance with EP 11-3-1.
• Post weld heat treatment shall preferably be done in a furnace. Stacking of components within the furnace shall not be permitted.
• Localized post weld heat treatment not done in a furnace may be accomplished by electric, resistance or induction heating subject to the following restrictions and written approval from the Owner's Engineer:
• A full circumferential band must be heated to the required temperature.
• Heater band shall extend five times the wall thickness on each side of the joint.
• Localized PWHT of longitudinal weld seams is not acceptable.
• (*)Gas firing shall not be used for post weld heat treatment without written approval of the Owner's Engineer.
• (*)Exothermic post weld heat treatment methods shall require written approval of the Owner's Engineer.
• (*)The post weld heat treatment temperature shall be 1150°F minimum, unless otherwise specified by the Owner's Engineer.
• The use of reduced PWHT temperatures with an extended hold time (per Table UCS-56-1 of the ASME Code, Section VIII, Division 1) is not acceptable.
• (*)Procedures for field PWHT shall be submitted for approval to the Owner's Engineer. These procedures shall include an acceptable method of insulating the tank floor and eliminating any heat sink effects due to contact with the ground.

POST WELD HEAT TREATMENT (PWHT) - AES

• Post weld heat treatment requirement for tanks in Aggressive Environmental Service (AES), see EP 10-2-1, shall be per paragraph 9.0.
• (*)Tanks in AES service that have been PWHT shall not be subject to additional welding without approval of the Owner's Engineer.

11.0 TABLES

TABLE 1

SMAW ELECTRODES FOR TANK WELDING CARBON STEEL MATERIALS P-1 GROUP OR P-1 GROUP 2(1)

NOTES:

• (*)Electrodes for all other materials shall have a review and approval from the fabricator and the Owner's Engineer.
• (*)Vertical down welding requires Owner's Engineer approval before final contract acceptance.
• E7024 (F-1 type) electrodes shall not be used for single pass fillet weld.

© 2026 Inflection Point Engineering, LLC. All rights reserved.