Steel pipe pressure bearing algorithm for black steel pipes

Steel pipe pressure bearing algorithm for black steel pipes

Black steel pipe production process flow

Round tube blank → heating → piercing → three-roll cross rolling, continuous rolling or extrusion → tube removal → sizing (or diameter reduction) → cooling → straightening → hydraulic test (or flaw detection) → marking → warehousing

Pressure bearing algorithm for black steel pipes

1: Calculating the pressure capacity of seamless steel pipes based on the outer diameter, specifications, and wall thickness of seamless steel pipes (different materials of steel pipes have different tensile strengths)
Pressure = (wall thickness * 2 * steel pipe material tensile strength) / (outer diameter * coefficient)

2: Calculation method for wall thickness based on knowing the outer diameter and pressure of seamless steel pipes:
Wall thickness = (pressure * outer diameter * coefficient) / (2 * tensile strength of steel pipe material)

3: Expression method of steel pipe pressure coefficient:
Pressure P＜7Mpa Coefficient S=8
7＜Steel pipe pressure P＜17.5 coefficient S=6
Pressure P＞17.5 Coefficient S=4 [2]

Mechanical properties of black steel pipe

The mechanical properties of large-diameter steel pipes are important indicators to ensure the final performance (mechanical properties) of large-diameter steel pipes. It depends on the chemical composition and heat treatment system of the steel pipes. Therefore, according to different usage requirements, the mechanical properties of large-diameter spiral steel pipes will be introduced in detail from the aspects of tensile strength, yield point, and elongation.

1. Tensile strength
During the stretching process, the maximum force (Fb) the sample endures when it breaks is the stress (σ) obtained by the original cross-sectional area (So) of the sample, which is called tensile strength (σb). The unit is N/mm2 (MPa). It represents the maximum ability of a metal material to resist damage under tension.

2. Yield point
For metal materials with yield phenomenon, the stress at which the sample can continue to elongate without increasing (remaining constant) force during the stretching process is called the yield point. If the force decreases, the upper and lower yield points should be distinguished. The unit of yield point is N/mm2 (MPa).

3. Elongation after break
In the tensile test, the percentage of the increased length of the gauge length of the specimen after it is broken to the original gauge length is called elongation. Expressed by σ, the unit is %.

Steel grade indication of black steel pipe

1. Carbon structural steel

① It consists of Q + number + quality grade symbol + deoxidation method symbol. Its steel number is prefixed with "Q", which represents the yield point of the steel. The following number represents the yield point value in MPa. For example, Q235 represents a carbon structural steel with a yield point (σs) of 235 MPa.
② If necessary, symbols indicating the quality grade and deoxidation method can be marked after the steel number. The quality grade symbols are A, B, C, and D respectively. The deoxidation method symbol F represents boiling steel, B represents semi-killed steel, Z represents killed steel, and TZ represents special killed steel. Killed steel does not need to be marked, that is, ZT and TZ do not need to be marked. For example, Q235-AF represents Grade A boiling steel.
③Special-purpose carbon steel, such as bridge steel, shipboard steel, etc., basically uses the representation method of carbon structural steel, but a letter indicating the purpose is appended to the end of the steel number.

2.High quality carbon structural steel

①The two digits at the beginning of the steel number indicate the carbon content of the steel, expressed as a few ten thousandths of the average carbon content. For example, for steel with an average carbon content of 0.45%, the steel number is "45". It is not a sequential number, so it cannot be read as 45 gauge steel.
② For high-quality carbon structural steel with high manganese content, the manganese element should be marked, such as 50Mn.
③ Boiled steel, semi-killed steel and special-purpose high-quality carbon structural steel should be specially marked at the end of the steel number. For example, semi-killed steel with an average carbon content of 0.1% has a steel number of 10b.

3. Carbon tool steel

①The steel number is marked with "T" to avoid confusion with other steel types.
②The number in the steel number indicates the carbon content, expressed as a few thousandths of the average carbon content. For example, "T8" indicates a uniform carbon content of 0.8%.
③ For those with higher manganese content, "Mn" will be marked at the end of the steel number, such as "T8Mn".

④ The phosphorus and sulfur content of high-grade high-quality carbon tool steel is lower than that of ordinary high-quality carbon tool steel. The letter "A" is added at the end of the steel number to indicate the difference, such as "T8MnA".

Large diameter steel pipe specification table
406*16	457*32	508*80	530*22	660*80	820*55
406*17	457*35	508*90	530*25	660*90	820*60
406*18	457*40	508*100	530*28	660*100	820*70
406*19	457*45	530*16	610*30	660*150	820*80
406*20	457*50	530*17	610*32	710*20	820*90
406*22	457*55	530*18	610*35	710*22	820*100
406*25	457*60	530*19	610*40	710*25	820*150
406*28	457*65	530*20	610*45	710*28	820*200
406*30	457*70	530*22	610*50	710*30	864*40
406*32	457*80	530*25	610*55	710*32	864*55
406*35	457*90	530*28	610*60	710*35	864*60
406*40	457*100	530*30	610*65	710*40	864*70
406*45	480*16	530*32	610*70	710*45	864*80
406*50	480*17	530*35	610*80	710*50	864*90
406*55	480*18	530*40	610*90	710*55	864*100
406*60	480*19	530*45	610*100	710*60	864*150
406*65	480*20	530*50	610*150	710*65	864*200
406*70	480*22	530*55	630*18	710*70	900*60
406*80	480*25	530*60	630*19	710*80	900*70
406*90	480*28	530*65	630*20	710*90	900*80
426*16	480*30	530*70	630*22	710*100	900*90
426*17	480*32	530*80	630*25	710*150	900*100
426*18	480*35	530*90	630*28	720*25	900*150
426*19	480*40	530*100	630*30	720*28	900*200
426*20	480*50	559*16	630*32	720*30	950*60
426*22	480*55	559*17	630*35	720*32	950*70
426*25	480*60	559*18	630*40	720*35	950*80
426*28	480*65	559*19	630*50	720*40	950*90
426*30	480*70	559*20	630*55	720*50	950*100
426*32	480*80	559*22	630*60	720*55	950*150
426*35	480*90	559*25	630*65	720*60	950*200
426*40	480*100	559*28	630*70	720*65	1000*80
426*45	508*16	559*30	630*80	720*70	1000*90
426*50	508*17	559*32	630*90	720*80	1000*100
426*55	508*18	559*35	630*100	720*90	1000*150
426*60	508*19	559*40	630*150	720*100	1000*200
426*70	508*20	559*50	660*20	720*150	1050*80
426*80	508*22	559*55	660*22	812.8*40	1050*90
426*90	508*25	559*60	660*25	812.8*45	1050*100
426*100	508*28	559*65	660*28	812.8*50	1050*150
457*16	508*30	559*70	660*30	812.8*55	1050*200
457*17	508*32	559*80	660*32	812.8*60	1100*80
457*18	508*35	559*90	660*35	812.8*70	1100*90
457*19	508*40	559*100	660*40	812.8*80	1100*100
457*20	508*50	610*16	660*50	812.8*90	1100*150
457*22	508*55	610*17	660*55	812.8*100	1100*200
457*25	508*60	610*18	660*60	812.8*150	1200*80
457*28	508*65	610*19	660*65	812.8*200	1200*90
457*30	508*70	610*20	660*70	820*50	1200*200