What Is Weld Joint Efficiency?
Quick Answer: Weld joint efficiency (E) is a de-rating factor between 0 and 1.0 applied to the allowable stress of a welded component. It accounts for the reduced reliability of a welded joint compared to seamless construction and depends on the joint type, degree of non-destructive examination (NDE), and the governing code.
How Weld Joint Efficiency Affects Design
The internal pressure design equation for a straight pipe per ASME B31.3 (Paragraph 304.1.2) is:
t = P x D / (2 x S x E x W + 2 x Y x P)
Where:
- t = minimum required wall thickness
- P = internal design pressure
- S = allowable stress for the material at design temperature
- E = weld joint efficiency factor (also called longitudinal joint quality factor)
- W = weld strength reduction factor (for high-temperature service)
- Y = coefficient based on material and temperature
A lower E factor requires a thicker pipe wall to contain the same pressure. For example, an ERW pipe with E = 0.85 needs approximately 18% more wall thickness than a seamless pipe (E = 1.0) for the same service.
Weld Joint Efficiency by Pipe Type (ASME B31.3, Table A-1B)
| Pipe Manufacturing Method | ASTM Specification | E Factor |
|---|---|---|
| Seamless | A106, A335, A312 seamless | 1.00 |
| ERW (Electric Resistance Welded) | A53 Type E, A135 | 0.85 |
| EFW (Electric Fusion Welded) | A671, A672, A691 | 0.85 (spot RT) to 1.00 (100% RT) |
| SAW (Submerged Arc Welded) | A671, A672 | 0.85 to 1.00 |
| Furnace butt welded | A53 Type F | 0.60 |
| Spiral welded | A139, API 5L PSL 1 spiral | 0.80 |
ASME Section VIII, Division 1 Joint Efficiency (Table UW-12)
For pressure vessels, weld joint efficiency depends on the joint category and extent of radiographic examination:
| Joint Type | Full RT (100%) | Spot RT | No RT |
|---|---|---|---|
| Type 1: Full-penetration butt, double-welded or equivalent | 1.00 | 0.85 | 0.70 |
| Type 2: Full-penetration butt, single-welded with backing | 0.90 | 0.80 | 0.65 |
| Type 3: Full-penetration butt, single-welded without backing | N/A | N/A | 0.60 |
| Type 4: Double fillet lap | N/A | N/A | 0.55 |
| Type 5: Single fillet lap, plug welds | N/A | N/A | 0.50 |
| Type 6: Single fillet lap, Category B/C | N/A | N/A | 0.45 |
Increasing the E Factor
The most common way to increase weld joint efficiency is to increase the extent of NDE:
- Moving from no RT to spot RT (per ASME VIII UW-52) raises E from 0.70 to 0.85 for a Type 1 joint
- Moving from spot RT to 100% RT raises E from 0.85 to 1.00
This trade-off between NDE cost and material cost is a key engineering decision: 100% radiography costs more in inspection but allows thinner walls and lighter piping, reducing material, welding, and support costs.
For piping, the weld joint efficiency is documented in the WPS and verified through weld mapping and NDE tracking during fabrication.
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