Learn the minimum distance between welds according to various standards like ASME, API, and BS. Understand key terms, spacing guidelines, and see examples to ensure safe and compliant welding practices. Understanding the minimum distance between welds is essential in piping and pressure vessel design. Different standards specify these distances to ensure weld strength, safety, and quality. Here’s a detailed guide covering various welding standards with explanations and real-world examples for minimum distance between welds.
Basics welding information
- Avoid heat-affected zone (HAZ) overlap and distortion.
- Maintain a typical minimum weld spacing of 3× thickness or 25 mm (whichever is greater).
- Follow applicable code requirements (e.g., ASME, AWS).
- Ensure adequate strength and reduce stress concentration.
- Allow proper cooling to preserve material properties.
Challenges facing during welding operation
- Limited space in complex assemblies or tight layouts.
- Spacing not considered during the design stage.
- Different standards (ASME, AWS, ISO) may have varying requirements.
- Closely spaced welds can increase residual stress and cause warping.
- Difficult to achieve proper spacing in hard-to-reach joints.
Key Takeaways
- Maintain 3× thickness or 25 mm minimum spacing.
- Prevent HAZ overlap and distortion.
- Reduce the risk of stress and cracking.
- Follow the relevant welding code requirements.
- Plan weld spacing early in the design phase.
Minimum Distance Between Welds with Explanations and Examples
| Standard/Spec | Minimum Distance Between Welds |
|---|---|
| ASME SEC VIII Pressure Vessel Code – 2017 | Longitudinal Welds (welds along the axis of cylindrical shells) should be spaced at least 5 times the wall thickness (5t), unless circumferential welds (running around the cylinder) are radiographically tested. Example: For a pressure vessel with 10 mm wall thickness, longitudinal welds should be spaced 50 mm apart. |
| ASME IX, 2013 | Circumferential welds require no minimum spacing if they pass Radiographic Testing (RT). In cases with multiple shell courses, longitudinal joints (along the vessel length) of adjacent courses must be offset by at least 5t. Example: For a shell with 12 mm thickness, longitudinal welds on adjacent courses should be 60 mm apart. |
| ASME B31.3 – 2016 | Longitudinal welds must be spaced by either 5t or staggered by 30 degrees, with no specific limit for circumferential welds. Example: For piping with 8 mm wall thickness, the minimum longitudinal weld spacing should be 40 mm. |
| ASME B31.4 – 2016 / ASME B31.8 – 2016 | Miter Joints (angled welds in a pipeline) should be spaced apart by half the Nominal Diameter (ND) of the pipe. Example: For a 10-inch pipe, miter welds should be spaced at least 5 inches apart. |
| API 5L/ISO 3183 – 2012 | Line pipe weld spacing: Longitudinal welds need 50–200 mm clearance, and Circumferential welds need 1500 mm. Example: In pipeline construction, longitudinal welds are spaced a minimum of 50 mm apart, and circumferential welds at least 1.5 meters. |
| API 650 – 2014 | Vertical Welds on tank shells should have a minimum distance of 5t. Example: For a tank shell 14 mm thick, vertical welds should be separated by at least 70 mm. |
| BS 2633 – 2006 | Minimum Weld Spacing for Nominal Thickness is 4t. Example: For pipes with a nominal wall thickness of 12 mm, weld spacing should be at least 48 mm. |
| BS 4515 – 2006 | Weld spacing should be 4 times the Pipe Thickness (4t). Example: For a pipe with 10 mm wall thickness, welds must be spaced 40 mm apart. |
| BS 2971– 2009 | Weld Spacing determined by mutual agreement. Example: For custom weld spacing on pipes, parties involved agree on requirements. |
| BS PD 5500 – 2014 | For Longitudinal Welds, maintain a minimum spacing of 4t or 100 mm. Example: With a 25 mm thick shell, the required spacing would be 100 mm. |
| AS 4458 | Circumferential welds should be spaced 4t or 30 mm; for Non-Pressure Parts, use the lower value of 3t or 40 mm. Example: In non-pressure applications with 10 mm thickness, weld spacing should be 30 mm. |
| AS 4041 – 2006 | Minimum spacing of 4t or 40 mm. Example: For a 10 mm thick component, welds should be at least 40 mm apart. |
| EN12952-5 -2001 | Butt Welds on Tubes: Minimum distance depends on Tube Diameter (D) and Tube Thickness (t). Example: For a tube with 200 mm diameter and t < 250 mm, spacing should be 2D, or 400 mm. |
| TOTAL GS EP PVV 171 – 2012 | Longitudinal Welds should be staggered by 30 degrees, and Circumferential Welds spaced 500 mm apart. Example: Longitudinal welds should be offset by 30 degrees for adjacent pipes, or separated by 500 mm if circumferential. |
| SHELL DEP 61.40.20.30 – 2011 | Circumferential welds: minimum spacing of 1D or 500 mm; branch/attachment welds: minimum 4t or 100 mm. Example: For an 8-inch pipe, circumferential welds need 8 inches of separation, or 500 mm, whichever is larger. |
| ARAMCO 32-SAMSS-004-2008 | For Shell-Head Welds, minimum spacing of 1 inch is required between shell-head and head-skirt welds. Example: Shell-head weld spacing should be at least 25.4 mm. |
| ARAMCO SAES-W-012 – 2008 | Longitudinal Welds on adjacent pipe joints should be 100 mm apart, and Butt Welds need a minimum of 20 mm or 3t, whichever is greater. Example: For an 8 mm thick pipe, butt weld spacing would be 24 mm. |
Key Terms Explained
- t (Thickness): Refers to the wall thickness of the welded component.
Example: For a pipe with 10 mm wall thickness, 5t means 50 mm. - RT (Radiographic Testing): A non-destructive test that uses X-rays or gamma rays to check the quality of welds without damaging the component.
- PWHT (Post Weld Heat Treatment): Heating a welded component after welding to relieve residual stresses or improve weld quality.
- Staggered Welds: Refers to offsetting welds to prevent alignment, which can improve joint strength.
- Miter Joint: A weld where two pipes are cut at an angle (other than 90 degrees) to join in a pipeline, often used in directional changes.
1. ASME SEC VIII Pressure Vessel Code – 2017
- Why it matters: When welding pressure vessels (like tanks and pipes under pressure), the spacing between welds is important to ensure the vessel can handle the pressure without weakening.
- Technical detail: The minimum distance between longitudinal welds (welds along the length of the cylinder) is 5 times the wall thickness (5t). This spacing helps prevent stress concentration and allows for better inspection and testing.
- Example: For a pressure vessel with a wall thickness of 10 mm, the minimum distance between two longitudinal welds should be 50 mm (5 × 10 mm = 50 mm).
2. ASME IX, 2013
- Why it matters: This standard is for the qualification of welding procedures and personnel, ensuring that welds are properly executed.
- Technical detail: If circumferential welds (welds around the cylinder) are radiographically tested (using X-rays or other imaging methods to check for defects), there is no minimum spacing required between them. However, when joining multiple shell courses (sections of a vessel), the longitudinal welds between adjacent courses must be offset by at least 5 times the wall thickness (5t).
- Example: For a shell with a 12 mm wall thickness, the longitudinal welds between sections must be at least 60 mm apart (5 × 12 mm = 60 mm).
3. ASME B31.3 – 2016
- Why it matters: This standard applies to piping systems, including those used in industries like chemical plants, power plants, and refineries. Proper weld spacing helps maintain pipe strength and integrity.
- Technical detail: Longitudinal welds (welds running along the pipe’s length) must be spaced at least 5 times the pipe thickness (5t) or staggered by 30 degrees to reduce the risk of stress points. Circumferential welds, which wrap around the pipe, do not have a minimum distance between welds but must still meet quality control standards.
- Example: For piping with an 8 mm wall thickness, the minimum distance between longitudinal welds should be 40 mm (5 × 8 mm = 40 mm).
4. ASME B31.4 – 2016 / ASME B31.8 – 2016
- Why it matters: These codes are used for pipeline construction, including for liquid and gas pipelines. Miter joints (angled pipe welds) must be spaced to avoid concentrated stresses at the joints.
- Technical detail: Miter joints should be spaced apart by at least half the Nominal Diameter (ND) of the pipe to prevent joint failure.
- Example: For a 10-inch pipe, the miter joints must be spaced at least 5 inches apart (half of 10 inches).
5. API 5L/ISO 3183 – 2012
- Why it matters: This standard is for line pipes, such as those used in pipelines that transport oil and gas. The weld spacing ensures proper joining and reduces defects that could cause leaks.
- Technical detail: The spacing for longitudinal welds in pipelines should range from 50 to 200 mm, depending on the pipe’s size and type. Circumferential welds need more clearance, usually 1500 mm apart.
- Example: In pipeline construction, longitudinal welds are spaced at least 50 mm apart, and circumferential welds must be at least 1.5 meters apart.
6. API 650 – 2014
- Why it matters: This code applies to the construction of storage tanks. Proper weld spacing helps maintain the tank’s structural integrity under pressure.
- Technical detail: The spacing between vertical welds (welds that run up and down on tank shells) should be at least 5 times the thickness of the tank shell.
- Example: For a tank shell with a 14 mm thickness, vertical minimum distance between welds should be spaced at least 70 mm apart (5 × 14 mm = 70 mm).
7. BS 2633 – 2006
- Why it matters: This standard focuses on pipe welding, where proper spacing reduces the risk of defects.
- Technical detail: The minimum weld spacing is 4 times the nominal thickness of the pipe (4t).
- Example: For a pipe with a 12 mm nominal wall thickness, welds should be spaced at least 48 mm apart (4 × 12 mm = 48 mm).
8. BS 4515 – 2006
- Why it matters: Similar to BS 2633, this code deals with welding on pipes and ensures weld spacing maintains the strength of the pipe.
- Technical detail: The weld spacing should be 4 times the pipe thickness (4t).
- Example: For a pipe with a 10 mm wall thickness, welds should be spaced at least 40 mm apart (4 × 10 mm = 40 mm).
9. BS 2971– 2009
- Why it matters: This is more flexible and allows for custom weld spacing depending on project requirements.
- Technical detail: Weld spacing is based on mutual agreement between the parties involved, so it can vary depending on the application and material.
- Example: For custom weld spacing, the specific spacing would be agreed upon by the involved parties.
10. BS PD 5500 – 2014
- Why it matters: This standard applies to pressure vessels and ensures that welds do not weaken the vessel.
- Technical detail: For longitudinal welds, the spacing should be either 4 times the thickness (4t) or a minimum of 100 mm.
- Example: For a shell with a 25 mm thickness, the minimum distance between welds spacing would be 100 mm.
11. AS 4458
- Why it matters: This standard applies to circumferential welds, ensuring that the welds on pressure vessels or pipes are spaced to prevent defects.
- Technical detail: Circumferential welds should be spaced at least 4t or 30 mm. For non-pressure applications, the spacing is reduced to 3t or 40 mm.
- Example: For a 10 mm thick non-pressure application, minimum distance between welds spaced 30 mm apart.
12. AS 4041 – 2006
- Why it matters: This code applies to the design and construction of pressure piping, helping to ensure that welds are adequately spaced to avoid weak points.
- Technical detail: Weld spacing should be 4 times the pipe thickness or 40 mm, whichever is greater.
- Example: For a 10 mm thick component, weld spacing should be at least 40 mm apart.
13. EN12952-5 -2001
- Why it matters: This standard applies to butt welds on tubes used in boilers and pressure equipment, ensuring proper weld spacing for tube integrity.
- Technical detail: For butt welds on tubes, the spacing depends on the tube diameter (D) and tube thickness (t). The minimum spacing should be 2 times the diameter (2D).
- Example: For a tube with a 200 mm diameter, the spacing between welds should be at least 400 mm (2 × 200 mm = 400 mm).
14. TOTAL GS EP PVV 171 – 2012
- Why it matters: This standard is used for pipelines and storage tanks, ensuring welds are spaced properly to avoid joint failure.
- Technical detail: Longitudinal welds should be staggered by 30 degrees from adjacent welds, and circumferential welds should be spaced at least 500 mm apart.
- Example: Longitudinal welds should be offset by 30 degrees, or if they are circumferential, they must be spaced 500 mm apart.
These standards ensure that welds are placed with enough space to maintain the strength and integrity of the materials being joined, prevent defects, and ensure safety during operation. minimum distance between welds should be followed.
FAQ
It’s the least amount of space that must be left between two separate weld joints to ensure the metal retains its strength and to prevent overlapping heat-affected zones.
2. Why is spacing between welds necessary?
Spacing controls heat concentration. Without it, excessive thermal buildup can distort the workpiece, weaken the joint, or create stress fractures over time.
3. How is the correct spacing calculated for minimum distance between welds
The value depends on welding standards, base material type, plate thickness, and weld size. Codes such as ASME, AWS, and ISO provide specific formulas or tables for determining it.
4. Are all codes consistent in their spacing rules for minimum distance between welds?
No. Each code or industry standard may set different requirements, depending on the application and the safety factors involved.
5. What problems arise when welds are too close?
Heat overlap can cause metallurgical damage, warping, hardness variations, and reduced fatigue life of the component.
6. Do different weld types require different spacing?
Yes. For example, butt joints, lap joints, and fillet welds can have varying minimum spacing requirements depending on geometry and load conditions.
7. Does material thickness influence the spacing requirement?
Absolutely. Thicker materials dissipate heat more effectively and may allow for shorter distances, while thinner materials usually demand greater separation.
8. Can the spacing requirement ever be reduced?
Only if an approved welding procedure or engineering assessment confirms that the joint will still meet design strength and safety requirements.
9. How can adequate spacing be achieved in compact designs?
By staggering welds, reducing weld size, or redesigning the joint layout to spread heat more evenly.
10. Which sectors pay close attention to weld spacing rules?
High-risk industries like oil and gas, shipbuilding, power generation, and aerospace apply strict spacing controls to maintain performance and safety.
Conclusion
In welding practice, the minimum distance between welds is not just a design detail—it is a fundamental element that influences the overall safety, durability, and performance of a structure. Whether working on pipelines, pressure vessels, or structural frameworks, adhering to the minimum distance between welds ensures that heat input from multiple joints does not overlap in a way that compromises material integrity.
Following recognized codes and standards when determining the minimum distance between welds helps avoid excessive thermal stress, distortion, and premature failure. This requirement also plays a critical role in extending the service life of components exposed to high loads, extreme temperatures, or corrosive environments. The minimum distance between welds is especially vital in industries like oil and gas, shipbuilding, and aerospace, where even small deviations from approved specifications can have serious consequences.
Designers and welders must plan their work so that the minimum distance between welds is always maintained, even in tight or complex assemblies. This often involves optimizing joint placement, staggering welds, or adjusting weld sizes to meet spacing guidelines. The minimum distance between welds is not just about heat management; it also directly impacts inspection efficiency, repair feasibility, and long-term maintenance requirements.
In high-pressure applications, ignoring the minimum distance between welds can lead to catastrophic failures. On the other hand, strict compliance ensures reliable performance under operational stresses. Even when exceptions are granted, they must be backed by engineering validation that confirms the modified minimum distance between welds will not affect safety or quality.
Ultimately, the minimum distance between welds is both a safety standard and a best practice. Respecting this principle supports stronger, longer-lasting welds and promotes the kind of workmanship that meets the highest industrial and regulatory expectations.