Welding of ship inspection castings is an important part of ship construction and maintenance, and its quality directly affects the safety and service life of the ship. Due to the special characteristics of casting materials, structures, and usage environments, special attention should be paid to the following key issues during the welding process:

1、 Preparation before welding

Material confirmation and inspection:

Strictly verify the material certificate of the casting to confirm whether its chemical composition, mechanical properties, etc. meet the specification requirements.

Conduct a visual inspection of the castings to ensure that there are no defects such as cracks, pores, shrinkage porosity, slag inclusions, etc. Perform non-destructive testing (such as ultrasound, radiation, etc.) when necessary.

Check the quality certificate of welding materials to ensure that they match the casting material and comply with the requirements of the classification society.

Groove design and processing:

Select the appropriate groove form (such as V-shaped, U-shaped, X-shaped, etc.) based on the thickness, material, and welding method of the casting.

The bevel angle, gap, and blunt edge size should be strictly controlled to ensure welding quality and reduce welding deformation.

Mechanical methods (such as milling, planing, etc.) should be used for groove processing to ensure that the groove surface is smooth, free of burrs, oxide scales, and other impurities.

Cleaning and preheating:

Thoroughly remove oil stains, rust, moisture, and other impurities from the groove and within a range of 20-30mm on both sides. Mechanical cleaning (such as wire brushes, grinding wheels, etc.) or chemical cleaning (such as solvent cleaning) can be used.

Determine whether preheating is required and the preheating temperature based on the casting material, thickness, and ambient temperature. Generally, carbon steel and low-alloy steel castings need to be preheated when the thickness is large or the ambient temperature is low, and the preheating temperature is usually 100-200 ℃.

2、 Welding process control

Welding method selection:

The commonly used welding methods for ship inspection castings include manual arc welding (SMAW), gas shielded welding (GMAW, FCAW), submerged arc welding (SAW), etc. The appropriate welding method should be selected based on the casting material, thickness, structural form, and production conditions.

For important parts or thick plate welding, multi-layer and multi pass welding can be used to reduce welding stress and deformation.

Welding parameter control:

Strictly control parameters such as welding current, voltage, and welding speed to ensure good weld formation and avoid defects such as incomplete penetration, undercutting, and porosity.

Using small wire energy welding to reduce embrittlement and deformation in the welding heat affected zone.

Welding sequence and direction:

Develop a reasonable welding sequence to control welding deformation and stress. The general principle is to weld symmetrically from the middle to both sides, or to use the segmented back welding method.

Pay attention to the welding direction and avoid extinguishing the arc in stress concentration areas.

Interlayer temperature control:

For multi-layer and multi pass welding, the interlayer temperature should be controlled to avoid a decrease in the performance of the weld metal caused by excessive temperature, or an increase in the tendency for cracks caused by insufficient temperature.

Defect handling:

If defects such as cracks, pores, and slag inclusions are found during the welding process, welding should be stopped immediately, and the defects should be removed before re welding.

3、 Post weld treatment

Post heat and heat treatment:

For materials that are prone to cracking or thick plate welding, post heating should be carried out immediately after welding to slow down the cooling rate and reduce welding stress.

Determine whether post weld heat treatment (such as annealing, normalizing, etc.) is necessary to improve the microstructure and properties of the weld and heat affected zone based on the casting material and specification requirements.

Visual inspection of welds:

After welding, conduct a visual inspection of the weld seam to ensure that it is well formed and free from defects such as cracks, undercutting, incomplete penetration, and surface porosity.

Non destructive testing:

According to the regulations and design requirements of the classification society, non-destructive testing (such as radiographic, ultrasonic, magnetic particle, penetrant, etc.) is carried out on the welds to ensure the internal quality of the welds.

Weld repair:

For non-conforming welds, the cause of the defect should be analyzed, and a repair process should be developed and approved before proceeding with the repair. After repair, re inspection is required.

4、 Other precautions

Welding environment:

Avoid welding in harsh environments such as rain, snow, and strong winds. When the ambient temperature is below 0 ℃, protective measures such as preheating should be taken.

Welder Qualification:

Welders must hold a welding certificate recognized by the classification society and engage in welding work for the corresponding project within the validity period.

Process evaluation:

The welding process must undergo welding process qualification (WPS) recognized by the classification society and be strictly implemented during construction.

Recording and tracing:

Keep records of various aspects during the welding process, including welding parameters, welding material batch numbers, welder information, etc., to ensure quality traceability.

5、 Common problems and preventive measures

crackle:

Causes: high tendency of material hardening, high welding stress, high hydrogen content, improper preheating or post heating, etc.

Preventive measures: Choose appropriate welding materials, control preheating and post heating temperatures, use low hydrogen welding rods, reduce welding stress, etc.

Pores:

Causes: Moisture in welding materials, impure protective gas, incomplete cleaning of grooves, etc.

Preventive measures: Dry welding materials, check protective gas, thoroughly clean grooves, etc.

Not fully welded:

Causes: The bevel angle or gap is too small, the welding current is too low, and the welding speed is too fast.

Preventive measures: Reasonable design of grooves, adjustment of welding parameters, etc.

In short, welding ship inspection castings is a highly technical and quality demanding job. Only by strictly controlling each link can welding quality be ensured and the requirements for safe navigation of ships be met.