Hardness and Rust Removal Methods of Thick-Walled Seamless Steel Pipes

Thick-walled seamless steel pipes have strong rigidity and hardness, so they are not easy to fold when used, and even bending is very difficult. However, this is not the case with counterfeit and inferior products. They may look like thick-walled steel pipes on the outside, but the thickness deep inside the steel pipe may not meet the corresponding standards. In the weaker parts, folding or bending is likely to occur. This method can be used to identify inferior seamless steel pipes.

In addition to these, most manufacturers of thick-walled seamless steel pipes have high production technology, and the production process they adopt is relatively smooth, and the surface of the products produced is very smooth. However, some products produced by small workshops do not have such characteristics. The surface looks uneven and even has very obvious defects. This is because their rolling process is not sophisticated enough. Therefore, this is also a way to identify the quality of seamless steel pipes. At the same time, the quality of these steel pipes can also be judged by checking whether there are cracks on the surface of seamless steel pipes. For stainless steel pipes, because of their relatively high strength, they are not easy to scratch. These methods can identify the quality of thick-walled seamless steel pipes.

How to continuously increase the wall thickness of seamless steel pipes?

1. Rolling tool installation

The center of the roller pitch and guide distance needs to be on the rolling line. The center line of the lead and roll spacing is on the center line of the piercing and rolling process, that is, the upper and lower roll spacings are equal, and the left and right lead spacings are equal.

2. Perforated ejector

The perforated mandrel is generally selected from thick-walled pipes with an outer diameter of Φ108mm-Φ114mm and a wall thickness of ≥25mm and uniform wall thickness.

3. Rolling mill mandrel

The core rod should be made of thick-walled tube with thick wall thickness. For the core rod with smaller specifications, solid billet can be used instead. Thick-walled tubes and solid blanks with uniform wall thickness can greatly reduce the probability of mandrel bending and deformation, and can improve the wall thickness accuracy of the steel tube.

4. Tube heating

The heating should be uniform, and the temperature should not be raised or lowered. Each temperature rise or fall should be steady and slow, and the maximum temperature rise or fall should not exceed 30℃.

5. Centering roller

Check whether the centering roller is installed in place, adjust the center of the relevant core roller, the opening angle and the opening size of each action to be consistent, and the center of the core roller should be on the rolling line.

6. Rolling center line

The rolling center line of the piercing machine is consistent with the center line of the piercing trolley to avoid "upward rolling" or "downward rolling" so that the tube billet is evenly stressed during piercing.

7. Rolling tools

Worn rolling tools such as top heads, guide plates, rollers, etc. should be replaced in time.

What are the methods for rust removal of seamless steel pipes?

1. Spray rust removal

The rust removal by jetting is to use a high-power motor to drive the jet blade to rotate at high speed, so that abrasives such as steel sand, steel shot, wire segments, minerals, etc. are sprayed on the surface of the seamless steel pipe under the action of centrifugal force. Not only can it handle rust, oxides and dirt, but also the seamless steel pipe can achieve the required uniform roughness under the violent impact and friction of the abrasive.

2. Rust removal of tools

Mainly use tools such as wire brushes to polish the steel surface, which can remove loose or raised oxide scale, rust, welding slag, etc. The rust removal of cold drawn seamless steel pipe can reach Sa2 level by hand tools and Sa3 level by power tools. If the steel surface is firmly attached to the iron oxide scale, the rust removal effect of the tool is not ideal, and the anchor pattern required by the construction cannot be achieved.

3. Cleaning

Clean steel surfaces using solvents and emulsions to remove oil, grease, dust, lubricants and similar substances. But it cannot remove rust, scale, welding flux, etc. on the surface of steel, so it is only used as an auxiliary means in production.

4. Pickling

Generally, chemical and electrolytic methods are used for pickling. Chemical pickling is used only for pipes to remove scale, rust, and old coatings. Sometimes it can be used as a re-treatment after sandblasting and rust removal. Although chemical cleaning can make the surface clean and rough, its anchor pattern is shallow and it is easy to pollute the environment.

The scar defect of seamless steel pipe refers to the pits similar to soybean size on the inner surface of seamless steel pipe. Generally speaking, most scars contain gray-brown or gray-black foreign bodies.

If we want to control the impact of scarring inside seamless steel pipes, we can consider the following three aspects:

core rod lubrication, deoxidizer and injection process. Poor mandrel lubrication or too low mandrel lubricant temperature will cause scarring inside the seamless steel pipe. In order to increase the core rod temperature, a method of cooling with cooling water only once can be adopted. The temperature of the mandrel needs to be strictly controlled during the production process. The surface temperature of the mandrel should be between 80-120°C before spraying the lubricant. The temperature of the mandrel should not be higher than 120°C for a long time, so that the lubricant on its surface is dry and dense before pre-piercing. The operator should frequently check the lubrication condition of the mandrel.

Read more : How to check the Quality of Thick-Walled Seamless Steel pipes ?

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