Why Idle LNG Ships Build Pressure: The 2 barg LNG Membrane Tank Revolution

Host: MyLNG Engineering

Channel: YouTube @ossati

Target Audience: Marine engineering students, fleet operators, naval architects, and LNG fuel technology specialists.

Episode Summary

Welcome to this special educational episode presented by MyLNG Engineering! In this episode, we tackle one of the most pressing operational dilemmas in modern cryogenic fuel management: why idle LNG-fueled ships build vapor pressure in port and how raising membrane fuel tank design pressure from the conventional 0.7 barg threshold up to 2 barg alters the thermodynamic equation.

Have you ever wondered why connecting an LNG-fueled vessel to Onshore Power Supply (OPS) can suddenly complicate boil-off gas (BOG) management? Or why increasing a tank's allowable design pressure to 2 barg provides a larger operational window without eliminating thermodynamic heat ingress? We unravel the thermodynamics, structural load requirements under the IGF Code alternative design process, and classification approvals from ClassNK and DNV that every maritime engineer needs to master.

Don't forget to subscribe to our YouTube channel @ossati for more deep dives into marine propulsion, LNG containment systems, and machinery space operations!

What You Will Learn in This Episode

• The Port Stay & Shore Power Dilemma:
• Why switching off auxiliary engines to plug into Onshore Power Supply (OPS) removes primary gas consumers onboard, transforming continuous heat ingress into rapid vapor pressure buildup.
• Thermodynamics of 0.7 barg vs. 1 barg vs. 2 barg:
• How increasing allowable relief valve settings (MARVS) from the atmospheric reference of 0.7 barg (~1.7 bar absolute) up to 2 barg (~3 bar absolute) expands the allowable pressure holding window without altering underlying boil-off rates.
• Alternative Design & Classification Approval:
• The step-by-step safety equivalence evaluation under the IGF Code required when exceeding 0.7 barg, including structural reinforcement against ~200 kN/m² differential pressure loads, fuel tank domes, gas handling, and hull integration assessed by DNV and ClassNK.
• Target Applications & Scaling Reality:
• Why 2 barg membrane containment is tailored for smaller fuel capacities on Pure Car and Truck Carriers (PCTCs), cruise liners (such as Le Commandant Charcot), and container feeders—and how it differs from the 1 barg Mark III Flex systems deployed on ultra-large container ships.

Key Engineering Takeaways

• Pressure Holding is an Operational Envelope: Raising design pressure provides operational flexibility to store warmer bunkered LNG and delay active gas disposal, but it does not stop thermodynamic heat ingress or BOG generation.
• Shore Power Alters Onboard Energy Balance: Utilizing OPS cuts berth emissions, but requires an approved BOG management strategy (such as dual-fuel boilers or expanded holding time) when engines are offline.
• Follow Framework & Flag Approval: Exceeding standard 0.7 barg IGF Code limits requires a project-specific alternative design validation with Flag Administration and Classification Society sign-off.

Connect With Us

• YouTube Channel: @ossati
• Produced by: MyLNG Engineering
• www: mylng.art