API 650 tanks- Joint Efficiency

[DravidGJ]

Hi All,

As per Appendix A, Cl A.3.4 The joint efficiency factor shall be 0.85 with the spot radiography required by A.5.3. By agreement between the Purchaser and the Manufacturer, the spot radiography may be omitted, and a joint efficiency factor of 0.70 shall be used.

My question is how the requirement for spot radiography is determined and what is the impact in thickness calculation?

Thanks in advance

 

[JStephen]

If you're asking, for a given tank, how you know which category it falls under- that should be specified by the owner in the data sheets. (And a lot of owners are open to working things differently if there is a preference or cost advantage to doing things one way or the other.)
If you're asking, how are the spot radiographs selected- there are rules for number and location of spot radiographs in API-650.
If you're asking, how did the people that wrote API-650 know how many radiographs should be used- that likely came from a lot of past experience and a committee vote. Similar issues arise with pressure vessels, and I assume in the ship-building industry.

Impact on thickness calculations- depends on the size of the tank. For small tanks where the minimum thickness requirements control the design, there may not be any impact.

 

[r6155]

DravidGJ's
Why don't you take an API 650 reading?
You can get a simple answer.

Regards

 

[GetAtMeWolf]

If you're asking about how many radiographs are required to be considered "spot" radiography, for a new-construction tank, see API-650, Section 8.1.2. Figure 8.1 gives you a good idea in determining this.

There are also limits placed on the size of tank that can be constructed without radiography (i.e. plates <=1/2" thk). Finally, this would affect the required construction thickness for each shell course, calculated in Section A.4.1.