According to Appendix A.3.4, the joint efficiency should be either 0.85 or 0.70. API-653 Section 2.3.3 also uses this value of joint efficiency. No other computations use this value, so the default of 1.0 can be left alone for variable point and one foot API-650 calculations.
According to API-620, the joint efficiency ranges from 0.35 to 1.0. Use Table 5-2 to determine the appropriate joint efficiency value for your tank design.
API-653 2nd Edition provides Table 2-1 for weld joint efficiencies if the original E value is unknown. This table is reproduced as follows:
|
Standard |
Edition & Year |
Joint Type |
Joint Efficiency E |
Applicability or Limits |
|---|---|---|---|---|
|
API-650 |
7th & Later |
Butt |
1.00 |
Basic Standard |
|
(1980-Present) |
Butt |
0.85 |
Appendix A - Spot RT |
|
|
|
Butt |
0.70 |
Appendix A - No RT |
|
|
1st - 6th |
Butt |
0.85 |
Basic Standard |
|
|
(1961-1978) |
Butt |
1.00 |
Appendices D&G |
|
|
API-12C |
14th & 15th |
Butt |
0.85 |
|
|
3rd-13th |
Lap (a) |
0.75 |
3/8 inch max t |
|
|
Butt (c) |
0.85 |
|
||
|
1st & 2nd |
Lap (a) |
0.70 |
7/16 inch max t |
|
|
Lap (b) |
0.50 + k/5 |
1/4 inch max t |
||
|
Butt (c) |
0.85 |
|
||
|
Unknown |
|
Lap (a) |
0.70 |
7/16 inch max t |
|
|
Lap (b) |
0.50 + k/5 |
1/4 inch max t |
|
|
|
Butt (c) |
0.85 |
|
|
|
|
Lap (d) |
0.35 |
|
|
(a) |
Full double lap welded. |
|
(b) |
Full fillet weld with at least 25% intermittent full fillet opposite side: |
|
(c) |
Single butt-welded joints with a back-up bar were permitted from the years of 1936 to 1940 and 1948 to 1954. |
|
(d) |
Single lap welded only. |