1. Continuously welded steel pipes
A steel pipe with a straight weld produced by the continuous welded steel pipe production process (this is a type of continuous butt-welded steel pipe).
2. PSL1 grade electric welded pipes
When the steel grade is higher than X42, the weld and the entire heat barrier zone should be treated similar to normalizing, unless the supplier and the buyer agree that heat treatment or a combination of heat treatment and chemical composition can be used instead.
When making such a substitution, the manufacturer should confirm the effectiveness of the process selected by both parties. It can include, but is not required to specify, hardness tests, microstructure assessments or mechanical property tests. For steel grades not higher than X42, the weld should be treated with similar heat treatment, or the steel pipe should be treated with appropriate heat processing technology so that no untempered martensitic structure remains.
Note: In the production process of electric welded steel pipes, the steel pipes pass through the air, and normalizing is usually defined as "cooling in still air", so the term "similar to normalizing heat treatment" is used.
3. PSL2 grade electric welded pipes
The minimum frequency of the welding machine used for the electric welding process should be 100kHz.
The weld seam and the entire heat barrier zone of all steel grades should be treated similar to normalizing, unless the supplier and the buyer agree that heat treatment or a combination of heat treatment and chemical composition can be used instead. When making such a substitution, the manufacturer should confirm the effectiveness of the process selected by both parties. It can include, but is not required to stipulate, hardness testing, microstructure evaluation or mechanical property testing.
4. Laser welded pipes
Steel pipes welded by laser welding process with a straight weld seam.
The weld seam and the entire heat barrier zone of laser welded pipes should be treated similar to normalizing, unless the supplier and the buyer agree to select an alternative process. When making such substitutions, the manufacturer shall confirm the effectiveness of the process selected by both parties. It can include, but is not required to include, hardness testing, microstructure evaluation or mechanical property testing.
Note: In the production process of laser welded pipes, the steel pipe passes through the air, and normalizing is usually defined as "cooling in still air", so the term "similar to normalizing heat treatment" is used.
5. Straight seam submerged arc welded pipe
A steel pipe with a straight weld seam welded by automatic submerged arc welding process. There are more than one inner and outer weld seams. (This type of steel pipe is often called submerged arc welded pipe.)
