Session: DA-22-01 Design and Analysis of Above Ground Liquid Storage Tanks

Paper Number: 154672

154672 - Stress Analysis and Fitness-for-Service Assessment of a Full Containment Steel-Steel Lng Tank for Major Leak Scenarios and Laboratory Testing of 9% Ni Steel Plates 

Abstract: 

Storage and containment systems are critical components of Liquefied Natural Gas (LNG) plants to ensure safe and reliable operations. Strict regulations are in place globally to ensure safety of operations of LNG tanks because of the amount of stored energy. Recent advancements in modern technologies for alloy production, testing methods, and construction techniques have contributed to improved performance and safety of LNG tanks. In this study, structural integrity of a FEED stage design of a 47-million-gallon capacity LNG tank with a secondary metal container was evaluated for various LNG release scenarios from the primary container. A secondary metal container is permitted in current versions of NFPA 59A and API 625; however, typical practice involves construction of concrete secondary containment systems. Nine percent Nickel steel (ASTM A553) secondary containment systems provide advantages in operation, maintenance, cost and construction schedule compared to a traditional reinforced concrete secondary containers for some projects. Therefore, this evaluation allows for the assessment of the performance and safety of a conceptual full containment steel-steel LNG tank subjected to sudden temperature drops due to exposure to LNG.

 

While properties of 9% Ni steel and welds at cryogenic temperature are available in the literature from testing programs in the 1970s and 1980s, less information is available on modern 9% Ni steel welded components. Laboratory testing of welded ASTM A553 steel plates was conducted with the welds perpendicular to the plate rolling direction and two heat inputs appropriate for vertical and flat welding configurations. Impact (Charpy V-notch) testing at temperatures ranging from room temperature to -196°C was conducted to determine the Charpy transition curve of the base metal and weldment. Quasi-static fracture toughness testing was also conducted to measure the J-integral resistance curves at -196°C. The cryogenic impact energy (Charpy) and fracture toughness (J) properties of the base metal and welds were compared with the published historical data and used for LNG tank assessments.

 

Global and local Finite Element (FE) models of the tank were developed to evaluate the structural response of the secondary metal container to cryogenic temperature (-168°C) exposure due to sudden LNG release load cases. The LNG release scenarios were developed from literature review and previous projects. Seismic aftershock following a major leak from the primary container during the main seismic shock was also considered. Although the conceptual design was developed for benign seismic loads on the Gulf Coast, we used seismic design criteria of Las Vegas, Nevada to represent a moderate seismic hazard. The stresses calculated from the FE analyses were compared with the allowable stresses in API 620. API 579 fitness-for-service (FFS) assessments with postulated flaws in the secondary container body and welds in multiple orientations were performed using demands from the stresses calculated in the FE analyses.

 

The study showed that the secondary container constructed of 9% Ni steel could safely withstand the loads resulting from the cryogenic release scenarios. The secondary container also met the performance criteria defined in API 620 for the aftershock hazard considered in the major leak plus seismic aftershock scenario. The FFS assessment results using our test data provided insights on the suitability of the type of nondestructive testing (NDT) methods for identifying the maximum flaw sizes that meet the acceptable performance according to the Level 2 FFS assessment procedure (API 579) based on the brittle fracture, ductile plastic collapse, or mixed failure modes. For most of the LNG release scenarios, visual inspection of the secondary container was sufficient to ensure that the tank would meet its design intent. The study provides fracture toughness values of welded 9% Ni steel plates’ base metal and weldment at cryogenic temperatures. The study also provides a methodology using detailed stress analysis and FFS assessments to evaluate the integrity of LNG storage containments for cryogenic spill scenarios and to establish permissible temperature drops in 9% Ni steels for the safe operation of the LNG storage containments for a range of accidental scenarios.

Presenting Author: Madhav Parikh Simpson Gumpertz & Heger Inc.

Presenting Author Biography: Mr. Parikh is a licensed professional civil engineer with over ten years of structural engineering experience. He has worked on numerous domestic and international oil and gas EPC projects. He has designed various steel and concrete plant structures, including piperacks, process structures, heater and reformer structures, and steel-clad buildings for both plant modifications and new facilities, many in high wind and high seismic regions. In recent years, Mr. Parikh has worked on investigations and failure analyses of elements and connections, wind and seismic evaluations of existing structures, and structural rehabilitation and repair designs. Mr. Parikh has experience in the design and evaluation of structures subjected to abnormal loads such as fire, blast, impact, and flood loads. Mr. Parikh is serving on the ASCE Energy Division Structural Fire Engineering Task Committee.

Authors:

Madhav Parikh Simpson Gumpertz & Heger Inc.
Onder Akinci Simpson Gumpertz & Heger Inc.
Steven D. Palkovic Simpson Gumpertz & Heger Inc.
Kareem Eltouny Simpson Gumpertz & Heger Inc.
Alan Humphreys Simpson Gumpertz & Heger Inc.
Guzhao Li Simpson Gumpertz & Heger Inc.
Nicholas Catella Simpson Gumpertz & Heger Inc.
Paul Summers Simpson Gumpertz & Heger Inc.