1. Manufacturing methods
(1) Hot rolled steel strip is used as blank, and temperature spiral forming is often used. Automatic submerged arc welding is used for spiral seam, and internal and external submerged arc welding is no less than one.
(2) Weld head is allowed on steel pipe, and the distance between pipe end and pipe end is not less than 300 mm. The buyer negotiates with the manufacturer to allow the head to be welded at the pipe end, but there should be at least 150 mm circumferential distance between the head and the corresponding pipe end screw wax.
(3) The butt joint allows two short pipe pipes of the same specification and type. The length of each short pipe should not be less than 2m. The circumferential weld should be staggered on both sides and the circumferential distance should be less than 150mm.


2. Types of steel
The range of standard steel pipe should be welded with Q195, Q215 and Q235 steel in GB/T700-1988. Note: Q refers to the back value of the yield strength of letters.


3. Hydraulic test
Each pipeline shall be subjected to a hydraulic test without leakage. The test pressure shall be measured by the S-hydraulic test where the test P = 2ST/D is located. The stress conditions of the hydraulic test shall be carried out according to the corresponding strip steel standards. The minimum output (Q235 235 Mpa) was selected at 60%. Regulator time: D < 508 test pressure holding time is not less than 5 seconds; D < 508 test pressure holding time is not less than 10 seconds


4. Nondestructive testing
X-ray or ultrasonic inspection shall be carried out for spiral pipe welds, steel strip welds and annular joints. For the spiral weld of flammable ordinary fluid conveying steel, 100% S X-ray or ultrasonic test should be carried out. Spiral welds of steel pipes for general fluid transportation, such as water, sewage, air and heated steam, should be examined by X-ray or ultrasonic (20%).




5. Defect Treatment
(1) The grinding wheel may be defective, but the remaining wall thickness must be within the allowable range.
(2) The minimum length of the weld is 50mm; the base metal after grinding shall not exceed 1.5mm.
(3) Remove defective sections within the allowable length range.
(4) Be judged to be unqualified.