API 650 Joint efficency

[VanceB]

In basic API 650 standard joint efficiency is equal to one. There are radiographic requirements for shell butt welds, the frequency determined by material thickness. However for floor and roof joints no radiography is required unless requested by purchaser. Does API 650 consider the roof and shell joint but weld JE=1 even though radiography is not an NDE requirement?
This question comes from a client who questioned how our company can prove floor JE=1 with no radiography.

Thanks in advance.

 

[JStephen]

For roofs significantly stressed by internal pressure, see F.6.2.
Otherwise, I'm not sure where a joint efficiency factor comes into play. The equations for supported cone roof thickness (ie, rafter span) and for self-supporting cone roof thickness are not based on joint efficiency.

 

[IFRs]

Adding my thoughts to JStephen's good answer: I don't think fillet welds would never have a joint efficiency of 100%, but it does not matter for the bottoms or roofs of these tanks. API 650 is based on the bottom of the tank being fully and uniformly supported and as such bottom welds are not structural but are part of a leak prevention barrier. Cone roofs are similar, they just have to be leak tight and don't experience membrane loading that would stress the welds in a significant way.

 

[HTURKAK]

.........Does API 650 consider the roof and shell joint but weld JE=1 even though radiography is not an NDE requirement?

JStephen (Mechanical) and IFRs (Petroleum) summarized the situation with good answers .


I just want to remind some exceptional and special cases .
As per API 650, RT is required for Shell vertical and horizontal welds in order to use JE =1.0 .One of the exceptional case, Refer to APPENDIX S .The shell thickness formula involves JE and JE=1.0 for Radiograph per 8.1.2 and JE= 0.70 if no radiography required .
API 620 approach differs from API 650 which allows fillet-welded shells with penalty in allowable stress (joint efficiency E=0.7 for Double full-fillet lap joint ).
As far as i understand, single fillet welds are allowed at API 650 for the roof and bottom plates lap joints of atmospheric tanks because they are not subject to high membrane stresses.