LNG Carrier Containment System: Difference between Membrance and Independant type

lovekobelxm
16th May 2012, 11:50
I know that Two major designs of the containment system are of the self supporting type, and the membrane type. But what is the major difference between the two design? Why is it called the "self-supporting" type, how is it self supported?(egg)

R58484956
16th May 2012, 12:10
Greetings LK and welcome to SN. Bon voyage.

JRMacGregor
16th May 2012, 12:13
I know that Two major designs of the containment system are of the self supporting type, and the membrane type. But what is the major difference between the two design? Why is it called the "self-supporting" type, how is it self supported?(egg)

When talking of LNG tanks, the "Moss type" is often used to mean the same as "independent self supporting type". And Moss is an ex shipbuilding town in your own country where this tank was developed. But you probably know this already.

These tanks are "self supporting" because they are very large diameter spheres with thick walls which are strong enough to keep their shape without external assistance - even when loaded with the cargo. They do not need any stiffening on the outside to support them.

As you can imagine, these spheres do need to be secured and held upright in the ship - to stop them rolling around etc. The spheres are therefore held by cylinders coming up from the bottom of the ship. These cylinders (sometimes known as a "skirt") make contact with the sphere at the "equator" of the sphere.

The above are called "independent" because the tank structure and the ship structure are basically independent of each other.

The membrane type is made of very thin metal and has no real strength in itself. The loads and forces created by the liquid in the tanks are transferred to the normal ship structure - which provides the strength. The ship inner hull "supports" the membrane. Between the metal membrane (very cold) and the normal ship structure (inner hull) is the insulation - which has to transfer these forces.

The membrane system is "dependent" on the strength of the ship structure (inner hull).

lovekobelxm
17th May 2012, 07:29
When talking of LNG tanks, the "Moss type" is often used to mean the same as "independent self supporting type". And Moss is an ex shipbuilding town in your own country where this tank was developed. But you probably know this already.

These tanks are "self supporting" because they are very large diameter spheres with thick walls which are strong enough to keep their shape without external assistance - even when loaded with the cargo. They do not need any stiffening on the outside to support them.

As you can imagine, these spheres do need to be secured and held upright in the ship - to stop them rolling around etc. The spheres are therefore held by cylinders coming up from the bottom of the ship. These cylinders (sometimes known as a "skirt") make contact with the sphere at the "equator" of the sphere.

The above are called "independent" because the tank structure and the ship structure are basically independent of each other.

The membrane type is made of very thin metal and has no real strength in itself. The loads and forces created by the liquid in the tanks are transferred to the normal ship structure - which provides the strength. The ship inner hull "supports" the membrane. Between the metal membrane (very cold) and the normal ship structure (inner hull) is the insulation - which has to transfer these forces.

The membrane system is "dependent" on the strength of the ship structure (inner hull).

Hello Sir

Thanks for the explanation, very clear and comprehensive!

Gulpers
17th May 2012, 11:54
lovekobelxm,

On behalf of the SN Moderating Team, a warm welcome aboard from the Isle of Anglesey!
You will thoroughly enjoy your time on SN and get many happy hours entertainment from your membership. (Thumb)