An industry survey on ‘repair rates’ was carried out by TWI in 2011 with the following conclusions:
- Repair rates for specific sectors and material grades are reported in the table below.
- Average repair rates for the Oil & Gas and Power sectors range from 1 to 3%. With peak rates up to 25% in specific locations and exceptional values up to 55%.
- Peak repair rates are typically observed in root runs, fillet welds and areas with limited access.
- The major factors perceived to affecting repair rates are welder’s skills, location or accessibility of welds and poor fit-up prior to welding (see figure below).
Average repair rates for different welded products and materials, according to TWI’s industry survey.
|
Type of product
|
Average repair rate, any material grades, %
|
Average repair rate per material grade, %
|
|
Mild steel
|
Stainless steel
|
Low-alloy steel
|
Ni-alloy
|
Low-temperature steel (eg Ni steel)
|
High strength steel
|
|
All products
|
-
|
2.0
|
2.2
|
3.1
|
3.4
|
2.2
|
-
|
|
Offshore structures (3)
|
2.0
|
2.1(1)
|
1.1
|
-
|
2.0(1)
|
2.2
|
-
|
|
Other welded structures (3)
|
1.0
|
1.5(1)
|
0.7
|
-
|
-
|
-
|
-
|
|
Piping systems (4)
|
3.0
|
1.7
|
3.5
|
4.2(1)
|
-
|
-
|
-
|
|
Pressure vessels (4)
|
2.0
|
2.8
|
1.1
|
0.5(2)
|
-
|
1.7
|
-
|
|
Offshore pipelines (4)
|
2.0
|
0.9
|
7.5
|
-
|
-
|
1.8
|
-
|
|
Onshore pipelines (4)
|
3.0
|
2.5(1)
|
-
|
2-5(2)
|
-
|
2-5(1)
|
-
|
|
Cryogenic storage tanks (4)
|
0.5(2)
|
-
|
0.5(2)
|
-
|
-
|
-
|
-
|
|
Hydroelectric turbines (3)
|
1-2(2)
|
1-2(2)
|
-
|
-
|
-
|
-
|
-
|
Notes:
- Based on less than 5 entries.
- Based on one entry.
- Average repair rate data provided as fraction of the length of repaired weld versus the total weld length.
- Average repair rate data provided as number of repaired welds versus the total number of welds.