Cave Filling LP versus HP tanks

[Charles2]

do you now by chance what the safety factors are for al and 3aa, mayber it is the reason why it is a SP tank.

The 3AL specification contains the following statement:

1. "Three samples must be pressurized to destruction and failure may not occur at less than 2.5 times the marked cylinder service pressure."

The 3AA specification does not contain any destructive or burst test; however, the specification is written such that the safety factor can be implied from the following two statements:

1. "For cylinders with service pressure of 900 psig or more the minimum wall must be such that the wall stress at the minimum specified test pressure may not exceed 67 percent of the minimum tensile strength of the steel"
2. "Each cylinder must be tested to at least 5/3 times the service pressure."

This would imply that the ratio of service pressure to burst pressure (assuming that the tank will burst when it reaches its tensile strength) is equal to 5/3÷0.67=2.488. Or, approximately 2.5 times the cylinder service pressure.

 

[Bob DBF]

?..assuming that the tank will burst when it reaches its tensile strength...

Tensile strength is the point where a metal goes from elastic deformation to plastic deformation. Hydros are done to make sure the tank has retained its elastic qualities. The tensile strength goes from from the point of plastic deformation until the metal fails. How much the metal stretches, plastic deformation, before it fails depends on the material composition.

Interesting article linked below.

What is Tensile Strength? - Definition from Corrosionpedia

There are three types of tensile strength:

1. Yield strength - The stress a material can withstand without permanent deformation
2. Ultimate strength - The maximum stress a material can withstand
3. Breaking strength - The stress coordinate on the stress-strain curve at the point of rupture

Bob

 

[Charles2]

Tensile strength is the point where a metal goes from elastic deformation to plastic deformation. Hydros are done to make sure the tank has retained its elastic qualities. The tensile strength goes from from the point of plastic deformation until the metal fails. How much the metal stretches, plastic deformation, before it fails depends on the material composition.

Bob

In older engineering textbooks as well as other articles of specification and design (The 3AA specification is quite old) the term 'tensile strength' is used to refer to the ultimate strength of the material. On most tables that list the properties of materials, there will usually be a column heading labeled "Tensile Strength" and then immediately adjacent will be a column heading labeled "Yield Strength".

The 3AL specification is much newer than the 3AA specification and does not use the term 'tensile strength' without qualifying as to whether it is yield strength or ultimate strength. Here is a quote from the same section of the 3AL spec:

• "The minimum wall thickness must be such that the wall stress at the minimum specified test pressure will not exceed 80 percent of the minimum yield strength nor exceed 67 percent of the minimum ultimate tensile strength..."