5.5 Fabrication of Large-diameter Coil-welded Steel Pipe
Ⅰ General Items
5.5.1 The butt weld on brazed steel pipe shall meet the following requirements:
1 The longitudinal seams on the same section should not be greater than 2.
2 The distance between 2 longitudinal seams should not be less than 200mm.
3 The distance between 2 longitudinal seams shall be larger than 100mm when pairing.
4 The distance between outer wall of branch and welding seam should not be less than 50mm.
Check quantity:10% random check for same type of elements，and at least 3 pieces.
Check method:observe and check with a steel rule.
5.5.2 The untight clearance between circle checking plate and inner wall of pipe shall meet the following requirements:
1 It shall be neither larger than 10% of wall thickness plus 2.0mm，nor more than 3.0mm at butt seam.
2 It shall not larger than 2.0mm at butt seam 200mm from pipe end，less than or equal to 1.0mm at other point.
Check quantity:10% random check for same type of elements，and at least 3 pieces.
Check method:check with a circle checking plate whose arched length is 1/6-1/4 of the pipe perimeter and steel rule.
5.5.3 The bustle pipe shall be pre-assembled and recorded during fabrication，the allowable preassembling deviation shall meet the requirements in Table 5.5.3.
Check quantity:full check for pre-assembling records，full check for allowable pre-assembling deviation.
Check method:check the pre-assembling records and take visual check.
Table 5.5.3 Allowable pre-assembling deviation of bustle pipe（mm）
Note:D refers to the diameter of pipe.
5.5.4 The allowable fabrication deviation of brazed steel pipe shall meet the requirements in Table 5.5.4.
Check quantity:10% random check for same type of elements，and at least 3 pieces.
Check method:see Table5.5.4.
Table 5.5.4 Allowable fabrication deviation of coil-welded steel pipe（mm）
Note:D refers to diameter of brazed pipe，d refers to flange diameter，L refers to length of pipe section.
5.5.5 The allowable deviation for main dimensions of welded elbow shall meet the following requirements:
1 Perimeter deviation:allowable deviation±4.0mm when Dg≤1000mm；
Allowable deviation±6.0mm when Dg＞1000mm.
Check quantity:10% random check for elbows，and at least 1 piece.
Check method:check with a steel rule.
2 Verticality deviation of end face and centerline:the value of△shall be neither larger than 1% of the outer diameter of pipe，nor larger than 3.0mm，as shown in Fig.5.5.5.
Check quantity:10% random check for elbows，and at least 1 piece.
Check method:check with a square and steel rule.
Fig.5.5.5 Verticality deviation of end face of welded elbow
Fig.5.5.6 Welded reducer pipe
5.5.6 The allowable deviation for main dimensions of welded reducer pipe shall meet the following requirements:
1 The roundness of reducer pipe shall be neither larger than 1% of the outer diameter at ends，nor larger than 5.0mm.
Check quantity:10% random check for reducer pipes，and at least 1 piece.
Check method:check with a steel rule.
2 The centerlines of concentric reducer pipes shall overlap and the deviation（a1-a2）/2 shall be neither larger than 1% of the outer diameter at ends，nor larger than 5.0mm，as shown in Fig.5.5.6.
Check quantity:10% random check for reducer pipes，and at least 1 piece.
Check method:pull a line and check with a steel rule.
5.5.7 The verticality deviation of branch of welded 3-way shall be neither larger than 1% of branch length，nor larger than 3.0mm.
Check quantity:10% random check for 3-ways，and at least 1 piece.
Check method:check with a square，hang plumb and check with a steel rule.