# Pressure bearing algorithm of large-diameter steel pipe

Posted by zora li on February 22nd, 2023

**Pressure bearing algorithm of large diameter steel pipe**

1. Knowing the outer diameter, specification and wall thickness of seamless steel pipe, the calculation method of bearing pressure (the tensile strength of different materials of steel pipe is different)

Pressure = (wall thickness * 2 * tensile strength of steel pipe material) / (outer diameter * coefficient)

2. Calculate the wall thickness by knowing the outer diameter of the seamless steel pipe and the bearing pressure:

Wall thickness = (pressure * outer diameter * coefficient) / (2 * tensile strength of steel pipe material)

3. The 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]

**Steel pipe weight formula**

[(outer diameter-wall thickness)*wall thickness]*0.02466=kg/m (weight per meter)

**Pipe diameter expression**

The expression of the diameter of large-diameter steel pipes shall meet the following requirements:

1 For water and gas transmission steel pipes (galvanized or non-galvanized), cast iron pipes and other pipes, the pipe diameter should be expressed in nominal diameter DN;

2 Seamless steel pipe, welded steel pipe (straight seam or spiral seam), copper pipe, stainless steel pipe and other pipe materials, the pipe diameter should be expressed by outer diameter × wall thickness;

3 For reinforced concrete (or concrete) pipes, clay pipes, acid-resistant ceramic pipes, cylinder tile pipes and other pipe materials, the pipe diameter should be expressed by the inner diameter d;

4 For plastic pipes, the pipe diameter should be expressed according to the method of product standards;

5 When the design uses the nominal diameter DN to indicate the pipe diameter, there should be a comparison table between the nominal diameter DN and the corresponding product specifications.

The specifications of rigid polyvinyl chloride pipes for building drainage are represented by de (nominal outer diameter) × e (nominal wall thickness) (GB 5836.1-92)

The specifications of polypropylene (PP) pipes for water supply are represented by de×e (nominal outer diameter×wall thickness)

**Delivery Length Regulations**

1. Normal length (also known as non-fixed length): Any length within the length range specified by the standard and without fixed length requirements is called normal length. For example, the structural pipe standard stipulates: hot rolled (extrusion, expansion) steel pipe 3000mm~12000mm; cold drawn (rolled) steel pipe 2000mm~10500mm.

2. Length to length: The length to length should be within the normal length range, which is a certain fixed length dimension required in the contract. However, it is impossible to cut out the absolute cut-to-length length in actual operation, so the standard stipulates the allowable positive deviation value for the cut-to-length length.

3. Double ruler length: The double ruler length should be within the usual length range. The single ruler length and the multiple of the total length should be specified in the contract (for example, 3000mm×3, which is a multiple of 3000mm, and the total length is 9000mm). In actual operation, an allowable positive deviation of 20mm should be added to the total length, plus a cut allowance should be left for each single ruler length. If there is no specification for the length deviation and cutting allowance in the standard, it should be negotiated by both the supplier and the buyer and indicated in the contract. The double-length scale is the same as the fixed-length length, which will greatly reduce the yield of the production enterprise. Therefore, it is reasonable for the production enterprise to raise the price, and the price increase range is basically the same as the fixed-length length increase.

4. Range length: The range length is within the usual length range. When the user requires a fixed range length, it must be specified in the contract.

**Production process**

Round tube billet→heating→piercing→three-roll cross rolling, continuous rolling or extrusion→pipe removal→sizing (or reducing)→cooling→straightening→hydraulic test (or flaw detection)→marking→storage

**Mechanical properties**

The mechanical properties of large-diameter steel pipes are important indicators to ensure the end-use performance (mechanical properties) of large-diameter steel pipes, which depend on the chemical composition and heat treatment system of the steel pipes. Therefore, according to different use requirements, the mechanical properties of large-diameter spiral steel pipes are specifically introduced from the aspects of tensile strength, yield point, and elongation.

1 Tensile strength

During the stretching process, the maximum force (Fb) that the sample bears when it breaks, and the stress (σ) obtained from the original cross-sectional area (So) of the sample is called the tensile strength (σb), and the unit is N/mm2 (MPa). It represents the maximum ability of metal materials 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 the force (keep constant) during the stretching process is called the yield point. If the force drops, 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 after the sample is broken to the original gauge length is called the elongation. Expressed in σ, the unit is %.