DL/T 1401-2015Steel pipe manufacturing technical requirements for steel structures of substation and transmission line (English PDF)

7.1 Steel

7.1.1 Steel for welding steel pipes shall be smelted by electric furnace or converter, if necessary, refining outside the furnace, and delivered in hot rolled state. If controlled rolling the condition of the steel must be agreed by the user and the process qualification of the corresponding welding method should be performed. The quality of steel should meet GB/T 700, GB/T 709, GB/T 1591, GB/T 3274, GB/T 3524 and other national standards and user requirements should have a steel plant quality certificate. If added in steel DL/T 1401-2015 Elements that refine grains should be indicated in the quality certificate. The steel pipe manufacturing enterprise shall carry out the inspection and acceptance in accordance with the content of the certificate and undergo re-inspection it can only be used after passing the test.

7.1.2 The surface of welded steel pipes shall be free from defects such as cracks, folds, scars, slag inclusions and heavy skins. When the surface is rusted, pitted or scratched, its depth should not be greater than 1/2 of the allowable negative deviation of the thickness of the steel, and the cumulative error should be within the allowable negative deviation. Surface defects of steel are not should be repaired by welding.

7.1.3 The steel for welded steel pipes shall be subjected to 100% ultrasonic testing within 25mm of the plate edge in accordance with GB/T 2970 and SY/T 6423.3 no cracks or delaminations are allowed. If the party has ultrasonic testing requirements for the board surface other than the edges on both sides, after consultation between the supply and demand sides, it is stated in the contract. The scanning area and acceptance level for testing shall be determined through consultation between the supplier and the buyer.

7.2 Welding materials

7.2.1 The quality of welding materials such as welding rods, wires, fluxes shall comply with GB/T 5117, GB/T 5293, GB/T 8110, GB/T 10045, GB/T 12470, GB/T 17493 and the requirements of users should have a welding material quality certificate. Steel tube manufacturing enterprises should Acceptance. The welding gas should meet the requirements of HG/T 2537 and HG/T 3728.

7.2.2 The use and storage of welding materials shall comply with JB/T 3223 standards.

7.2.3 The selection of welding consumables should match the mechanical properties of the base metal, and each batch of welding consumables can only be used after passing the re-inspection.

8.1 Process selection

8.1.1 For steel pipes with an outside diameter not greater than 299mm, straight seam high-frequency resistance welded steel pipes (HFW) or seamless steel pipes (SMLS) should be selected.

8.1.2 Straight seam high frequency resistance welded steel pipe (HFW) and straight seam submerged arc welded steel pipe (SAWL), combined gas-shielded and submerged arc welded steel pipe (COWL), spiral seam submerged arc welded steel pipe (SAWH) or seamless steel pipe (SMLS).

8.1.3 Steel pipes with an outside diameter of more than 508mm should be selected from straight seam submerged arc welded steel pipes (SAWL), combined gas shielded welding and submerged arc welding (COWL) or spiral seam submerged arc welded steel pipe (SAWH).

8.2 Welded steel tube manufacturing process

8.2.1 Straight seam high-frequency resistance welded steel pipe (HFW) with an outer diameter greater than 219 mm or a yield strength of not less than 420 MPa shall respond to the weld and heat after welding the affected area undergoes on-line normalizing heat treatment.

8.2.2 Straight seam high frequency resistance welded steel pipe (HFW), straight seam submerged arc welded steel pipe (SAWL), and combined gas welding and submerged arc welding steel the pipe (COWL) can be used for sizing or expanding the steel pipe by cold sizing or cold expanding method. The sizing rate of cold sizing steel pipes should not be greater than 0.015;

The sizing ratio of cold-expanded steel pipes shall not be less than 0.003, and shall not be greater than 0.015.

The sizing ratio of steel pipes can be calculated according to the following formula.

Sr = | Da-Db |/Db

In the formula.

Sr-sizing ratio of steel pipe;

Da-the outer diameter of the steel pipe after sizing designed by the manufacturer, in millimeters (mm);

Db-the outer diameter of the steel pipe before sizing designed by the manufacturer, in millimeters (mm).

8.2.3 Straight seam high-frequency resistance welded steel pipe (HFW), straight seam submerged arc welded steel pipe (SAWL), and combined gas welding and submerged arc welding steel when the outer diameter of the pipe (COWL) is not greater than 800mm, a maximum of one longitudinal weld is allowed. When the outer diameter is greater than 800mm and not greater than 1600mm, Two longitudinal welds are allowed, and up to 3 longitudinal welds are allowed when the outer diameter is greater than 1600mm.

8.2.4 Welded steel pipes are not allowed to have circumferential butt welds, and spiral seam submerged arc welded steel pipes (SAWH) are not allowed to have butt joints of steel strips.

8.3 Delivery status

Straight seam submerged arc welded steel pipe (SAWL), straight seam gas shielded and submerged arc welded steel pipe (COWL) and spiral seam submerged arc welded steel pipe (SAWH) should be delivered in the welded state, and straight seam high-frequency resistance welded steel pipes (HFW) should be delivered in the welded or welded heat treated state.

DL/T 1401-2015

9.1 Cutting

9.1.1 The cutting of steel plates or steel strips can be performed by mechanical cutting, plasma cutting or flame cutting. When using mechanical shearing method, various brands the maximum allowable cold-shear thickness of No. steel should meet the requirements of Table 1. When the thickness of the steel exceeds 10mm, the cold-cut edge should be milled or planed.

Edge processing. When using plasma cutting or flame cutting, the overheated area should be removed before forming.

Table 1 Allowable maximum cold shear thickness Unit. mm

Maximum shear thickness of steel grade Q235 24 Q345 20 Q390 16 Q420 14 Q460 12

9.1.2 When cutting by mechanical shearing method, the minimum allowable shearing temperature of various grades of steel shall meet the requirements of Table 2. Temperature is lower than Table 2 when stipulated, the cutting edge should be milled or planed.

Table 2 Allowable minimum shear temperature unit. °C

Minimum shear temperature of steel grade Q235 -5 Q345 0 Q390, Q420, Q460 5

9.1.3 After processing, the edge of the plate shall be smooth, neat and crack-free. The size of the groove and the quality of the edge of the plate shall meet the requirements of welding quality. Width of steel plate after cutting the degree and deviation should meet the requirements of the outer diameter deviation of the steel pipe after forming.

9.1.4 The width of the steel strip used to manufacture the spiral seam submerged arc welded steel pipe (SAWH) should not be less than 0.8 times the outer diameter of the steel pipe, and should not be larger than the steel pipe.

3 times the outer diameter.

9.2 Pre-bending and forming

9.2.1 The surface of the steel plate or strip should be inspected before forming. When the surface is rusted, pitted or scratched, the surface can be ground.

The international thickness shall meet the minimum wall thickness requirements of steel pipes after pipe making.

9.2.2 The deformation of the steel plate or strip during pre-bending and forming shall be uniform. After the pre-bending, the edge of the plate shall be smoothly transitioned. The pre-bending width and radian shall meet the requirements of the tube shape.

It is required that the formed steel pipe should have no obvious indentation and straight edges.

9.3 Welding

9.3.1 Welding procedure qualification

Straight seam submerged arc welded steel pipe (SAWL), straight seam gas shielded welding and submerged arc welding steel pipe (COWL) or spiral seam submerged arc welded steel pipe (SAWH) Manufacturers of steel, welding materials, welding methods, preheating and post-weld heat treatment, etc. for the first time before steel pipe welding Welding procedure qualification shall be performed in accordance with the provisions of GB 50661, and a welding procedure specification shall be prepared. For straight seam high frequency resistance welded steel pipe (HFW) Manufacturers should first prepare welding procedures and test welded joints with reference to the test items of GB 50661. Welding range of welding parts the range should not exceed the coverage of the welding procedure qualification.

9.3.2 Welder qualification

9.3.2.1 Welders shall undergo special basic theoretical and operational skills training and pass the examination to obtain a certificate of conformity.

9.3.2.2 The type of steel to be welded and the welding method shall be consistent with the items passed by the welder in his own examination, and welding shall not be performed beyond the scope.

DL/T 1401-2015

9.3.3 General requirements for welding

9.3.3.1 Welding equipment. The working condition of the welding equipment shall be intact, and the display instruments such as welding current, welding voltage and welding speed shall be verified.

Use within the validity period.

9.3.3.2 Weld quality grade. The quality grade of steel pipe welds shall be in accordance with the design requirements of the power transmission and transformation steel structure and specified in the purchase contract, but not Lower than the requirements of the third-level weld, and completely penetrated.

9.3.3.3 Requirements for welding environment.

a) The storage warehouse of welding materials shall be kept dry and the relative humidity shall not exceed 60%.

b) Welding should not be applied when any of the following conditions occur in the welding work area without effective protective measures.

--The wind speed is greater than 2m/s during gas shielded welding;

-Relative humidity is greater than 90%;

-There is cross-wind or fan air in the welding operation area in the production workshop;

-The surface of the weldment is wet or covered with snow and ice.

9.3.3.4 Pre-heating and post-weld heat treatment. When pre-heating and post-weld heat treatment are required in the welding process qualification or design documents, pre-heating shall be carried out in accordance with regulations.

Heat and post-weld heat treatment. In the following cases, the butt welding should be in the range of greater than or equal to 2 times the thickness of the steel plate and not less than 100 mm in each direction at the beginning of welding.

Pieces for preheating.

-When welding steel grades below Q345, the ambient temperature is below -10 ° C;

-When welding Q345 grade steel, the ambient temperature is lower than 0 °C;

-When welding steel grades above Q345, the ambient temperature is below 5 ° C.

9.3.3.5 It is strictly forbidden to embed metallic materials in the gap between welds.

9.3.4 Weld quality

9.3.4.1 Weld appearance quality

9.3.4.1.1 The look and feel of the weld should be. uniform shape, good shape, smooth transition between the bead and weld bead, weld and base metal, Spills are removed.

9.3.4.1.2 When the appearance of the weld is one of the following, the surface shall be non-destructively tested for defects.

-When cracks are found in the visual inspection, 100% surface non-destructive testing should be performed on the welds of this batch of steel pipes-When a crack is suspected in the appearance inspection, the surface of the suspected part shall be subjected to non-destructive testing;

-When the order requires surface non-destructive testing;

-When inspectors consider it necessary.

9.3.4.1.3 The appearance quality of welds shall meet the requirements in Table 3.

Table 3 Weld quality grade and appearance defect classification unit. mm

Project tolerance

Weld quality level 1 level 2 level 3 Exterior defect not full (Refers to insufficient design requirements) Depth <=0.2 0.02t and <=1.0, the total defect length per 100.0 welds is not greater than 25.0 Undercutting is not allowed Depth <=0.05t and <=0.5; continuous length <=100.0 and total length of undercut on both sides of the weld <=10% full length of weld Depth <=0.1t and <=1.0, unlimited length Crater cracks are not allowed Arc abrasions are not allowed to allow individual arc abrasions Splash clear Bad joints are not allowed Notch depth <=0.05t and <=0.5 Notch depth <=0.1t and <=1.0 no more than 1 weld per 1000.0 DL/T 1401-2015

Table 3 (continued)

Project tolerance

Weld quality level 1 level 2 level 3 Exterior defect Welding is not allowed Surface slag inclusions are not allowed to have a depth of <=0.2t, a length of <=0.5t and <=20.0 Surface pores are not allowed

Note 1. t is the nominal thickness of the steel pipe.

Note 2. If the undercut is ground and trimmed and smoothly transitioned, it is only evaluated according to the minimum allowable thickness of the weld.

9.3.4.2 Weld seam dimensions

9.3.4.2.1 Weld residual height C

Straight seam submerged arc welded steel pipe (SAWL), straight seam gas shielded and submerged arc welded steel pipe (COWL) and spiral seam submerged arc welded steel pipe the allowable deviation of the remaining height of the weld (SAWH) shall meet the requirements of Table 4. The remaining height of the inner and outer welds within 150mm of the pipe end should be smoothed, and the remaining height the degree is not more than 0.5mm.

Table 4 Allowable deviation of weld remaining height Unit. mm

Project allowable deviation diagram Weld seam height C First level, second level ...