API 620 – Design and Construction of Large Welded Low-Pressure Storage Tanks

Systematically assess your large welded low-pressure storage tank design and construction programme against API 620 — covering scope and pressure limits, materials for low-temperature and cryogenic service, tank geometry constraints, shell and roof design under combined pressure and liquid head, welding procedures and NDE, pneumatic and hydrostatic testing, and Appendix Q requirements for LNG and cryogenic storage tanks.

API 620 (13th Edition) Up to 103 kPa (15 psi) Internal Pressure Appendix Q – LNG / Cryogenic Combined Pressure + Liquid Head Design Full Radiography Required Auto-Save Enabled

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✓ Compliant: 0 ~ Partial: 0 ✗ Gap: 0 — N/A: 0 ○ Not Assessed: 0

🧊 Fabricator / Owner & Tank Design Details

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TOPIC: GeneralMaterials DesignShell BottomRoof NozzlesWelding NDETesting LNG/Cryo AppendixRecords All Std Low-P LNG/Cryo

API 620 Tank Gap Analysis Report

Executive summary and section compliance overview for API 620 Large Welded Low-Pressure Storage Tanks.

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ISO Xpert – Your API 620 Low-Pressure Tank Quality Partner

Expert API 620 tank design and construction quality consulting — gap analysis, ITP development, cryogenic material qualification, 9% nickel steel welding procedure support, NDE programme review, and API 620 Appendix Q LNG tank compliance assessment.
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Last Updated: April 2025 | ISO Xpert Ltd

For legitimate internal API 620 tank quality assessment. Results are indicative — not a substitute for a formal API 620 inspection. API 620 is the property of the American Petroleum Institute. ISO Xpert Ltd is not affiliated with API. Governed by English and Welsh law.

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API 620 Large Welded Low-Pressure Storage Tanks — Frequently Asked Questions

Authoritative answers about API 620 Large Welded Low-Pressure Storage Tanks, inspection intervals, qualifications, RBI, and ISO Xpert consulting.

What is API 620?

API 620 is the American Petroleum Institute standard for the Design and Construction of Large Welded Low-Pressure Storage Tanks. It applies to large, field-erected, vertical cylindrical tanks operating at internal pressures up to 103 kPa (15 psig) gauge. It covers a wider pressure range than API 650 (which is essentially atmospheric) and provides rules for designing tanks under combined pressure and liquid head loading.

What pressure range does API 620 cover?

API 620 applies to tanks designed for internal pressures up to 103 kPa (15 psig). This makes it applicable for: low-pressure gas storage, tanks storing volatile liquids under vapour pressure, refrigerated/cryogenic storage tanks (Appendix Q and R), and large diameter tanks where the pressure-shell interaction must be rigorously designed. Tanks operating at or near atmospheric pressure only are governed by API 650.

What is API 620 Appendix Q?

API 620 Appendix Q covers the design of low-pressure storage tanks for cryogenic service, specifically for Liquefied Natural Gas (LNG) and similar refrigerated products. Appendix Q provides additional requirements for: materials suitable for cryogenic temperatures (9% nickel steel, austenitic stainless steel, aluminium alloys), thermal insulation design, inner shell and outer jacket design (double-wall tanks), special welding requirements, NDE at cryogenic service temperatures, and cool-down procedures.

What NDE is required by API 620?

API 620 requires more extensive NDE than API 650 due to the higher pressures involved. Requirements include: RT of shell butt welds (extent per the design joint efficiency used), RT of dome and curved roof welds, magnetic particle or liquid penetrant testing of nozzle welds, full RT of all welds for Appendix Q cryogenic tanks, and vacuum box testing of bottom plate welds. All vertical shell seam welds must be fully radiographed in API 620 tanks.

Can ISO Xpert help with API 620 tank quality management?

Yes. ISO Xpert provides API 620 tank design and fabrication gap analysis, ITP review, welding procedure qualification support, NDE programme review, material certification review for low-temperature and cryogenic materials, and quality management system development. Contact us at info@iso-xpert.com or call +44 7853 109840.

API 620 – Design and Construction of Large Welded Low-Pressure Storage Tanks

🧊 Fabricator / Owner & Tank Design Details

API 620 Tank Gap Analysis Report

ISO Xpert – Your API 620 Low-Pressure Tank Quality Partner

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API 620 Large Welded Low-Pressure Storage Tanks — Frequently Asked Questions

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