PetroStreet

I have to estimate the time required to weld 25 weld joints in 8" Sch. 80 piping for an upcoming short shutdown of one facility.
Please share how can I correctly estimate in addition to get an estimate from welders and their supervisors.

Which welding processes are you planning to use?

GTAW for root and hot pass and SMAW from remaining passes.

Time of welding can be calculated by using the following formula:
T = W / (D x K)
where,
T = welding time
W = total weight of weld metal (for 8" NPS Sch. 80 welds with V-groove, take weight as 1.5 kg/m length for steel)*
D = deposition rate (depends upon the welding current with SMAW, for 120 A take 2 kg/hr max.)
K = Operating factor (take 25-30% for GTAW / SMAW)

W can be calculated as:
W = S x N x C
where,
S = Cross sectional area of weld joint
N = length of the weld joint
C = specific gravity of weld metal

Calculations for your case assuming welding of steel:
Total length to be welded (m) = 25 (no. of welds) x 0.6882 (length of each weld) = 17.21
W (kg) = 1.5 (* see above) x 17.21 = 25.82

Welding time (hrs) = 25.82 / (2 * 0.25) = 51.64

Hope this would give you some idea.

Thank you very much mechcolor.
It is indeed very useful.
Can you share the reference for values like weight/length for welds with double V-groove, J-groove and deposition rates.

Very useful formula.

arcpro
These and many other very helpful calculations have been given in "AWS Handbook - Economics of Welding & Cutting".

Mechalor,

Thanx for sharing. Really useful
NAQ