Stainless Steel Pipe and Water Tank Welding

The primary national standards for stainless steel pipeline welding include GB/T 12459-2005 “Steel Butt-Welded Elbows,” GB/T 12460-2005 “Steel Butt-Welded Tees,” and GB/T 13401-2005 “Steel Butt-Welded Pipe Fittings,” among others. Yuanjie Water Supply and Distribution Systems exclusively use sanitary-grade 304 stainless steel piping.

I. Construction Preparation

1. The welded stainless steel water tank is fabricated using high-quality SUS304 or 316L stainless steel plates and glass-fiber-reinforced plastic panels. The materials are cut to size according to the tank specifications, then undergo a series of processing steps, including shearing, film lamination, pressing, shaping, alignment, and final inspection before being delivered as qualified products.

2. Prior to construction, thoroughly review the construction drawings and relevant technical documentation; verify the water tank construction drawings against the structural and architectural drawings; familiarize yourself with the water tank installation process; understand the construction and acceptance criteria; and prepare a construction plan.

3. Prior to construction, the power supply at the construction site must be secured. Electrical power for construction shall be arranged through consultation with the construction contractor, but must be sufficient to meet operational requirements.

4. The construction site shall be well-organized and maintained in a dry, well-ventilated working environment.

5. The strip foundation for the water tank shall comply with the drawings and installation requirements; its height shall not be less than 200 mm, and the deviation in foundation height for all units shall not exceed 5 mm.

6. A dedicated person shall be assigned to manage the construction site, responsible for the comprehensive management of the construction teams and for conducting full-process supervision of the water tank quality.

- Material Preparation

1. Raw materials such as welding wire and welding electrodes shall undergo quality inspection, and their chemical composition, mechanical properties, and weldability shall comply with national standards.

2. Stainless steel pressed plates shall be carefully inspected upon arrival and prior to use to ensure compliance with the relevant quality and technical requirements.

3. The channel steel base frame shall be thoroughly inspected upon arrival and prior to use, and must comply with the relevant quality and technical requirements.

4. Stainless steel tie rods and vertical posts shall be thoroughly inspected upon arrival at the site and prior to use to ensure compliance with applicable quality and technical requirements.

II. Major Equipment Preparation

1. Equipment: TIG welder, electric welder, angle grinder, argon gas cylinder, power distribution box, etc.

2. Tools: adjustable wrench, hand hammer, screwdriver, wire cutters, cutting tools, welding equipment, etc.

3. Measuring tools: spirit level, steel tape measure, plumb bob, calipers, protractor, chalk line, etc.

III. Installation Process Flow
Pre-welding preparation procedures

( 1) Production drawings and processes

Prior to welding, it is essential to thoroughly familiarize oneself with the fabrication process drawings and procedures for the welded structure; this is a critical step in ensuring the smooth production of welded components. The main aspects include the following:

The product’s structural configuration, the types of materials used, and the technical requirements;

Dimensions of the product’s welded areas, as well as the structural configuration of the weld joints and bevels;

The welding methods employed, including welding current, welding voltage, welding speed, and welding sequence, as well as the control of preheating and interpass temperatures during the welding process;

Post-weld heat treatment procedures, inspection methods for welded components, and quality requirements for welded products.

( 2 ) Base Material Preprocessing and Cutting

1 ) Base Material Pre-treatment

The pre-treatment of metallic structural materials primarily refers to the straightening and surface treatment of steel prior to its use. If strict adherence to relevant operating procedures is not maintained during lifting, transportation, and storage, steel often develops various types of deformation, such as overall bending, local bending, and wave-like distortion, rendering it unsuitable for direct use in production and necessitating correction.

Sheet metal correction is commonly performed using multi-roll leveling machines, and coiled steel plates can also be leveled using such machines after being uncoiled.

2 ) Material cutting

Material shall be cut using mechanical thermal cutting, with each piece clearly marked with the product name, drawing number, specifications, graphical symbols, and hole diameters, and may only be used after passing inspection. The dimensional tolerances for manual scribing and template fabrication shall comply with the relevant standards, taking into account weld shrinkage and machining allowances.

When cutting and blanking stainless steel plates, attention should be paid to work-hardening near the cut edge.

3 ) Groove machining

To ensure that the weld thickness meets the specified dimensions, to prevent welding defects, and to achieve full-penetration weld joints, the edges of the weld shall be prepared into various groove configurations in accordance with the plate thickness and the requirements of the welding procedure.

1. 1. On-site welding procedure

( 1 ) Welding sequence

1 ) Welded chassis

Determine the spacing of the channel steel based on the dimensions of the water tank section. First, tack weld the channel steel in place, then use a level to verify that it is perfectly horizontal and flush before completing the full weld.

2 ) Fixed base plate

The water tank bottom plate that has passed inspection Place On the channel steel frame (Apply anti-rust paint to the front channel steel before installation to prevent galvanic corrosion.) 。

Note: The channel steel surface is coated with anti-rust paint. The function of anti-rust paint is to prevent metal from rusting and to enhance the adhesion of the coating. After applying anti-rust paint to metal, it effectively isolates the metal from contact with air; moreover, the paint induces passivation on the metal surface, thereby inhibiting chemical or electrochemical reactions between the metal and other substances and achieving corrosion protection. In addition, since the anti-rust paint reacts with the metal surface to form a passivation layer, the bond between the paint and the metal not only involves physical adhesion but also chemical bonding, resulting in exceptionally strong adhesion. Effectively isolates the channel steel from direct contact with the stainless steel plate, ensuring that the water quality inside the tank meets the required standards.

3 ) Fixed side panel

Weld the inspected and qualified tank pressure plates to the tank bottom plate by spot welding in sequence, securing each plate as

Thereafter, use a level and plumb bob to check the verticality of each panel; only proceed with tack welding the next panel once verification confirms accuracy, continuing this process until all side panels have been tack-welded.

4 ) Fixed cover板

The water tank cover plate, which has passed inspection, is securely fastened to the side panels, with vertical support columns installed between the center of the cover plate and the tank bottom to ensure overall flatness.

5 ) Install accessories

Secure the internal tie rods according to the water tank structure, and install the inner and outer ladders.

6 ) Open hole

Cut openings at the locations and according to the pipe diameters specified in the drawings, and tack-weld the flanged stub pipes for each opening. The flanges must be installed with the required horizontal and vertical alignment.

7 ) Perform overall welding of the water tank. , requiring that the weld be free of defects such as porosity, blowholes, and slag inclusions.

( 2 ) Welding Process

1) Welders must comply with According to the “Examination Regulations,” personnel may only commence on-the-job welding after passing the relevant test-piece examination.

2) It is strictly prohibited to strike an arc, conduct test currents, or weld temporary supports on the surface of the workpiece being welded without authorization.

3) The TIG welding torch and the argon gas pressure-reducing flow meter used by welders shall be inspected regularly to ensure that the argon gas flows in laminar fashion during the root pass of TIG welding.

4) Prior to joining, the bevel surface and the inner and outer walls of the base metal shall be thoroughly cleaned to remove oil, paint, scale, rust, and other contaminants until a metallic luster is exposed. The cleaning scope shall extend to each side by 10–15 mm, with a joint gap of 2.5–3.5 mm.

5) The joint gap must be uniform and straight; forced alignment is prohibited, and the misalignment shall be less than the wall thickness. 10%, and not greater than 1 mm.

6) When the local gap at the interface is excessive, it shall be reworked; the insertion of shims or packing materials into the gap is strictly prohibited.

7) After the interface passes inspection, it should be evaluated based on the varying interface lengths. At 4–5 o’clock, the tack-welding material shall be the same as that used for the final weld, with a tack-weld length of 10–15 mm and a thickness of 3–4 mm.

8) After completing the root pass, the quality of the root weld shall be carefully inspected, and only after confirming it meets the requirements shall the argon arc overlay welding be carried out.

9) Arc initiation and arc termination must be performed within the joint gap; during arc termination, the molten pool must be completely filled, and the arc should be guided toward the groove to extinguish it.

10) For spot welding, TIG welding, and cap pass welding, if defects occur, they must be ground away using an electric grinding tool before welding can resume; re-melting to eliminate defects is prohibited.

11) Attention should be paid to the quality of weld joints and arc termination; ensure good fusion at the joint and completely fill the weld pool when terminating the arc. To ensure Verify the tightness of the weld.

12) Upon completion of the cover pass, slag and spatter on the weld surface shall be promptly removed.

( 3 ) Causes of Defects in Argon Arc Welding and Methods for Their Prevention

Weld Defect	Causes	Prevention methods
Stomata	Impure argon, a ruptured gas hose, or moisture in the gas supply line can cause tungsten contamination, with metal fumes entering the weld pool.	Switch to pure argon, inspect the gas supply system, grind or replace the tungsten electrode, and thoroughly clean the weld joint.
Poor penetration results in weld bumps.	Uneven welding speed and lack of technical proficiency.	Strengthen fundamental skills training and maintain a consistent welding speed.
Severe black and gray oxidation of the weld seam	Low argon flow, slow welding speed, high temperature, or high current.	Increase the argon flow rate, increase the welding speed, or reduce the current appropriately.
Shrinkage porosity	Improper arc termination method results in abrupt arc cessation.	Change the arc termination method and stop by increasing the welding speed.
Crack	Welding temperature is too high or too low, resulting in poor penetration or overheating.	Ensure full penetration; adjust the welding current and travel speed appropriately, and change the arc termination position.
Incomplete penetration	Fast welding speed, low current	Reduce the welding speed or increase the current.
Poor fusion	Misalignment, incorrect torch angle, or excessive travel speed with insufficient current.	Improve the alignment to minimize misalignment errors, maintain an optimal welding gun angle, and appropriately reduce the welding speed while increasing the current.
Burn through	Inadequate technique, high current, or slow welding speed.	Reduce the current or increase the welding speed, and strengthen fundamental skills training.
Surface impact damage to the weld seam	Arc initiation is inaccurate, and the ground wire contact is poor.	Arc striking must be precise; arc striking on the surface of the workpiece is prohibited, and the ground lead must be properly connected.
Tungsten Inclusion in Weld Seam	Strike the tungsten electrode; the tungsten electrode makes contact with the workpiece.	During arc initiation, the tungsten electrode must be kept at a certain distance from the workpiece.
Uneven weld bead formation	Uneven gun travel speed, uneven wire feed speed.	Maintain consistent welding speed and wire feed, and intensify fundamental skills training.
Bite edge	Incorrect torch angle, uneven weld pool temperature, and improper wire feed.	Adjust the welding torch angle to ensure uniform molten pool temperature, and pay close attention to the position, timing, and speed of wire feed.

Hydrostatic Pressure Test for Sealing Performance

After welding is complete, wipe all welded joints dry with a dry towel, then fill the tank with water to the marked capacity and let it stand. After 24 hours, wipe all welded joints again with a dry towel; the towel should show no signs of moisture.

Water Tank Cleaning and Disinfection

The service water tank must be thoroughly cleaned before it is put into service. During cleaning, workers must wear plastic shoe covers before entering the tank to carry out the cleaning. First, use a cleaning agent to scrub away dirt and grime inside the tank, then flush the interior with tap water until the effluent is free of particulates and clear and transparent—only then is the tank considered compliant.

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