Limitations for Longitudinal weld length

[HMALY]

Does the code limits the length of a longitudinal weld in circular ducting? For example, if I have a 42 ft long duct, 20 ft diameter. The duct will be supplied to the site in 3 longitudinal sections (each section 42 ft long). At site, the 3 sections will be field welded longitudinally.
Does the code restrict such long longitudinal weld?
Do I need to break the continuation of the weld by adding keys in the duct?

Thanks

 

[weldstan]

There is no restriction in D1.1; however, proper precautions must be taken to mitigate undue growth during welding. Use of long, more frequent, tack welds, back step welding techniques, etc. may be required.