LNG Tank Welding Application | Isso Mak
The welding process for liquefied natural gas (LNG) tanks includes several steps and considerations to ensure the integrity and safety of the tank.
LNG Tank Welding process is done by following the steps below.
  • ​​Source Standards: LNG tank source must comply with industry standards and regulations, which may vary by country and project characteristics. Common standards include the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and the International Organization for Standardization (ISO) standards.
  • Material Selection: LNG tanks are typically made using low temperature carbon steel or 9% nickel steel due to their ability to withstand the extremely low temperatures of liquefied natural gas. The base metal and filler materials must have suitable mechanical properties and be suitable for cryogenic service conditions.
  • Welding Techniques: Various welding techniques can be used in LNG tank construction, including shielded metal arc welding (SMAW), gas tungsten arc welding (GTAW or TIG), and gas metal arc welding (GMAW or MIG). The choice of welding technique depends on factors such as joint design, material thickness and project requirements.
  • Joint Design: LNG tanks typically use double-sided welded connections to ensure adequate strength and sealing. Joint design may include single or double slope configurations with or without support strip, depending on the design of the tank and resource requirements.
  • Preparations Before Welding: Before welding, thorough cleaning and surface preparation is essential to remove contaminants that can affect the quality of the weld. This may include processes such as grinding, degreasing and preheating.
  • Welding Process: The welding process itself involves the application of precise heat to melt the base metal and filler material, creating a fusion between the components. Welders must adhere to the appropriate welding procedure specifications (WPS) provided by the project's engineering team. WPS summarizes key parameters such as heat input, welding technique, electrode type and preheat/postheat requirements.
  • Non-Destructive Testing (NDT): After welding, comprehensive non-destructive testing is performed to verify the quality and integrity of the welds. Commonly used NDT methods for LNG tank sources include radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT), and liquid penetrant testing (PT).
  • Post Weld Heat Treatment (PWHT): Depending on material and project requirements, post weld heat treatment may be necessary to relieve residual stresses and improve the mechanical properties of welded joints. PWHT typically includes controlled heating and cooling processes performed according to specific temperature-time profiles.
  • Inspection and Quality Assurance: Inspection and quality control measures are applied throughout the welding process to ensure compliance with applicable standards. Qualified weld inspectors monitor weld quality, dimensions, and alignment while conducting visual inspections and coordinating NDT activities.