Procedures For Welding Of Pressure Pipes

- Aug 23, 2017 -


1.scope of application

This procedure is applicable to industrial pipe or utility piping material for carbon steel, low alloy steel, heat-resistant steel, stainless steel and dissimilar steel pressure pipe welding rod arc welding and tungsten argon arc welding and co2 gas shielded welding welding construction.

 

2. Main compilation basis

2.1 gb50236-98 "on-site equipment, industrial pipeline welding engineering construction and acceptance specification";

 

2.2 GB/t20801-2006 "pressure piping specification - industrial pipeline";

 

2.3 sh3501-2001: construction and acceptance specifications of petrochemical highly toxic and combustible media pipelines;

 

2.4 gb50235-97 "specification for construction and acceptance of industrial metal pipes";

 

2.5 cjj28-89 "construction and acceptance specification of urban heating pipe network";

 

2.6 cjj33-89 "urban gas transmission and distribution engineering construction and acceptance specification";

 

2.7 GB/t5117-1995 carbon steel electrode;

 

2.8 GB/T5118-1995 "low alloy steel electrode";

 

2.9 GB/t983-1995 "stainless steel electrode";

 

2.10 YB/t4242-1984 "stainless steel wire for welding";

 

2.11 GB1300-77 "welding steel wire";

 

2.12 other current relevant standards, specifications and technical documents.

 

3 construction preparation

3.1 technical preparation

 

3.1.1 pressure pipe welding before construction, should according to the design documents and reference standard, specification, welding procedure qualification report according to my company of welding technical files (welding procedure card or wi).If the company is the first steel to be welded, the welding process evaluation guide should be developed first, then the process evaluation test of the material will be carried out, and the welding process evaluation report shall be made after the qualification.

 

3.1.2 technical documents compiled by the welding process, welding process card or wi) must according to the engineering practice, a detailed description of the design of the pipeline material, choose welding method, welding material, joint type, specific welding construction craft, weld quality requirements, inspection requirements, and heat treatment after welding (such as when required).

 

3.1.3 before the pressure pipeline is welded, the welders and the relevant personnel shall be subject to the technical disclosure according to the instructions of the welding operation.

 

3.1.4 pressure piping for high temperature, high pressure, highly toxic, flammable and explosive, should be drawn before welding construction, so as to conduct quality control in welding construction.

 

3.2 requirements for materials

 

3.2.1 the welded pipe (piece) must have a quality certificate, and its quality conforms to the requirements of the current national standard (or the standard of the ministry);The imported materials shall meet the technical conditions specified in the national standard or contract.

 

3.2.2 the quality of welding materials (electrode, wire, tungsten bar, argon, carbon dioxide, oxygen, acetylene, etc.) must conform to the national standard (or industry standard) and have a certificate of quality.The tungsten rod is suitable for cerium tungsten rod.The purity of argon should not be lower than 99.95%;The purity of carbon dioxide is not less than 99.5%;Water content is no more than 0.005%.

 

3.2.3 the pressure piping shall be made and installed on the site to meet the required welding material warehouse and welding rod drying room, and the welding rod shall be dried and welded by the special person, and the drying and issuing records shall be completed.

 

3.3 welding equipment

 

3.3.1 welding machines and equipment mainly includes: ac welding machine, dc welding machine, argon arc welding machine, high temperature drying box, medium temperature drying oven, incubator, co2 gas shielded welding machine, welding electrode insulation tube, internal grinding machine and electric polishing machine, etc.

 

3.3.2 all kinds of welders used for welding of pressure pipes must be equipped with ammeter, voltmeter, and regularly calibrated according to the requirements, and the parameters of welding specifications should be flexible.

 

3.4 welding personnel

 

3.4.1 track of pressure pipe welder should have according to the special equipment operating personnel evaluation rules of examination qualified welder certificate, and the qualified projects and welds, and in the period of validity.

 

3.4.2 welding rod drying personnel and welding rod warehouse management shall be strictly implemented in accordance with the welding procedure control procedures of the company.

 

3.5 welding environment

 

3.5.1 the wind speed of welding shall not exceed the following provisions, and the wind protection shall be provided when the provisions are exceeded.

A) manual arc welding: 8m/s;

B) argon arc welding, carbon dioxide gas shielded welding: 2m/s.

 

3.5.2 the relative humidity of the welding arc 1m shall not be greater than 90%.

 

3.5.3 to set up protective shelters when welding on rain and snow;When the surface of the welding piece is wet, the tube (piece) which is not preheated should be roasted to remove the moisture.

 

3.5.4 the minimum ambient temperature allowed during welding is as follows:

Carbon steel: - 20 ℃;Low alloy steel: - 10 ℃;High alloy steel: 0 ℃.

 

 

4 welding process

4.1 welding construction flow chart of pressure pipeline

 

 

4.2 preparation and joint pairs before welding

 

4.2.1 the welding method of pressure pipeline shall be carried out according to the design rules. When the design is not specified, the welding method can be chosen according to the wall thickness.When the wall thickness is less than 6mm, the sealing surface technology of argon arc welding or argon arc welding is optional.When the wall thickness > 6mm, the welding process can be done with argon arc welding and manual arc welding.

 

4.2.2 the selection of welding materials shall be designed according to the design. If the design is not specified, the design shall be selected according to table 1, table 2 and table 3, and the following requirements shall be met:

A) when welding of the same pipe (piece), the weld metal performance and chemical composition shall be equivalent to the mother material, and the welding process performance is good.

B) the selection of welding rod or wire shall meet the following requirements:

When both sides of the pipe are non-austenitic stainless steel, the optional components are in between the two sides or with the low side of the alloy to match the welding rod, wire.

For austenitic stainless steel, a stainless steel electrode with high nickel content can be used.

 

4.2.3 the groove form, size and group of welding joints shall be implemented according to the design rules, and shall be determined according to table 4 when the design is not specified.

 

4.2.4 pipe groove should be processed according to the following methods:

A) by SH3501-2001 "petroleum chemical industry highly toxic, flammable medium pipeline engineering code for construction and acceptance of SHA level is divided into three parts: the pressure pipeline, high alloy steel and stainless steel pipe groove mechanical processing method should be adopted.

B) other pipe groove should be machined by means of mechanical method. When the heat processing method is adopted, the surface layer which affects the welding quality must be removed after cutting.

 

4.2.5 the same pipes (pieces) of the wall shall be flush with the inside wall. If there is a fault, the wrong mouth value shall be carried out according to the design rules. When the design is not specified, the following requirements shall be followed:

A) highly toxic, flammable and explosive pipes are 10% of the wall thickness and not more than 0.5mm.

B) the local fault of the high temperature, high pressure and alloy steel pipes is 10% of wall thickness and no greater than 1.0mm.

C) the local fault of other pipes is 10% of wall thickness and not greater than 1.5mm.

4.2.6 when the tube (piece) of the wall thickness is different, the thickness of the thick wall tube shall be thinned.

 

4.2.7 the piping weld shall be set up to avoid the stress concentration area and be convenient for welding, heat treatment and various tests.

 

4.2.8 welded joint group of the former, application of chipping on both sides of groove and its internal and external surface, within the scope of 20 mm on both sides of groove can not have paint, burr, rusty spot, scale and other harmful to the welding quality of material, and grinding the metallic luster.

 

4.2.9 carefully check for defects such as cracks and interlayer on the groove and its sides.

 

4.2.10 when the stainless steel pipe is arc welding, it shall be coated with white powder or other anti-stain agent on both sides of the groove.

 

4.2.11 when the welding parts are assembled, the welded pipe (piece) shall be securely attached to prevent deformation and additional stress during welding and heat treatment.

 

4.2.12 in addition to the cold drawing of the design, the other welding joints should be prohibited from the strong group, and the thermal expansion method should not be used to prevent the additional stress.

 

4.2.13 when the welding place is in a high position, the qualified welder shall perform the same simulated practice and test welding before the welding, which can be formally welded after the non-destructive testing.

 

4.2.14 the group should try to correct the size of the tube mouth when it is too large, and it is strictly prohibited to fill it in the gap.

 

4.2.15 welding rod shall be dried according to its instructions before use, and shall be kept in the insulation tube for use.Before the wire is used, remove oil stains and rust stains on its surface

.

 

4.3 position welding

 

4.3.1 the welding materials, welding process and preheating temperature shall be the same as the welding materials, and the following requirements shall be met:

A) positioning welding shall ensure that the welds shall not be cracked during the formal application of the welding process. The length of the welding seam shall be 10 ~ 15mm, and the height shall be 2 ~ 4mm, and not more than 2/3 of the thickness of the wall.The ends of the weld seam should be ground to a gentle slope.

B) location welding shall not have any cracks or any other defects, such as any defects should be thoroughly ground and resoldered.

C) the material and welding material of the card shall be the same as the pipe material when the welding set is positioned on the wall of alloy steel pipe.When removing the fixture, no tapping or twisting can be used to remove it.When cutting the card with oxy-acetylene flame, it should be cut at 3mm from the surface of the pipe, and then grinding with grinding wheel.

 

4.4 official welding

 

4.4.1 the welding arc shall be carried out in the groove, and it is strictly forbidden to ignite the electric arc, test current or welding temporary support on the surface of the pipe (piece).

 

4.4.2 in welding, the arc and arc should be ensured, the arc crater should be filled and the layer of multi-layer welding shall be staggered.

 

4.4.3 in addition to the welding process have special requirements, finish each weld shall be a continuous welding, such as forced to interrupt, slow cooling measures should be taken, welding should be carefully check again after confirmation no crack, can according to the welding welding process to continue.The tube materials that have preheating requirements should be reheated after preheating according to preheating requirements.

 

4.4.4 when the pipe is welded, the end of the pipe shall be blocked to prevent draught inside the pipe.

 

4.4.5 welding process parameters are selected according to table 5 and table 6.

 

4.4.6 according to the design and welding process, the pre-heating pipe shall be preheated before welding.

The specific procedures shall be carried out in accordance with the relevant provisions of the general heat treatment procedure for pressure piping.

 

4.4.7 when the argon arc welding is adopted, the weld should be checked in time, and the sealing surface shall be welded as soon as possible to prevent cracks.

 

4.4.8 in the process of welding, the temperature of the interlayer shall not be lower than the lower limit of the preheating temperature.

 

4.4.9 if the pipe (piece) of high alloy steel (with chromium content is greater than 3% or the total amount of > 5%) is welded, the inner wall shall be filled with argon or mixed gas to prevent the oxidation or overburning of the root layer.

 

4.4.10 welding of large diameter thick wall pipe should use multilayer step by step a multipass welding for welding, argon arc welding backing welding layer thickness is not less than 3 mm, each layer by the self-check qualified rear can welding time, until finished.

 

4.4.11 to reduce welding deformation and stress, a tube with a diameter of more than 194mm shall be welded with symmetry of two persons.

 

4.4.12 the concealed weld for inspection shall be inspected and qualified before any other procedure is performed.

 

4.4.13 low temperature steel, austenitic stainless steel, heat-resistant and corrosion-resistant high alloy steel, and austenitic and non-austenite steel joints shall meet the following requirements:

A) should be in within the prescribed scope of welding working instruction, under the condition of good to ensure that the weld penetration and fusion, a small current, short, fast arc welding speed and multilayer multipass welding process, and temperature should be controlled between the layers.

B) the welding seam with high corrosion resistance required high double weld shall be soldered at last.

C) after welding of low temperature steel, it is advisable to treat the weld surface annealing.

D) austenitic stainless steel weld and its adjacent surface shall be treated with pickling and passivation.

 

4.4.14 the work fixture used in the pipe cold drawing shall be removed after welding and heat treatment work.

 

4.4.15 welders and solders welded to the pipe hanger shall be the same as the pipe welding requirements.

The welding seam is strong, the shape is beautiful, and there is no defect. In the welding process, it is necessary to prevent the welding of the pipe and prevent the deformation.

 

4.4.16 solder welding shall be cleaned after welding. After self-inspection, the welding operator shall be labeled in the vicinity of the weld, and shall record the welding work in the corresponding pipeline.

 

 

 


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