Technical requirements for steel pipes

 
1. Technical basis for steel pipe production
The product standard of steel pipe is the technical basis for the organization of steel pipe production on site, the assessment standard of steel pipe products, and a technical agreement that can be reached by the supply and demand sides under the current production level.
The contents of general national and industry standards are as follows:
1) Variety, that is, the specifications of steel pipe products. It stipulates the cross-sectional shape, unit weight, geometric size and allowable deviation of various steel pipe products.
2) Technical conditions, that is, the quality standards (or performance standards) of steel pipe products. It stipulates the chemical composition, mechanical properties, process properties, surface quality and other special requirements of steel pipe products.
3) Acceptance rules and test methods, that is, inspection standards for steel pipe products. The rules for inspection and acceptance and the sampling locations for testing are specified. At the same time, the shape and size, test conditions and test methods of the sample are also specified.
4) Packaging, marking and quality certificate, that is, the delivery standard of steel pipe products. It stipulates the packaging requirements, marking methods, and filling out quality certificates when the finished tubes are delivered for acceptance.
 
 
2. Requirements for dimensional deviation of steel pipes
Each standard has its own steel pipe size deviation.

 
3. Length requirements of steel pipes
The length requirements of steel pipes can be divided into ordinary length, fixed length and double length.
 
Usual length
Steel pipes are delivered in normal lengths. Usually the length should meet the following requirements: Hot rolled tube: 3000 ~ 12000mm; Cold rolled tube: 2000 ~ 10500mm
The length of hot-rolled short gauge tube is not less than 2m, and the length of cold-rolled short gauge tube is not less than 1m.
 
Fixed length and double length
The fixed length and double length should be within the normal length range, and the allowable deviation of the full length is divided into three levels. The allowance for each doubling length is as follows:
Outer diameter ≤159mm: 5 ~ 10mm;
Outer diameter> 159mm: 5 ~ 10mm.
 

 

Full length allowable deviation level	Allowable deviation of full length, mm
L1	0～20
L2	0～10
L3	0～5

 
 
 
4.Shape
The requirements for the external dimensions of the steel pipe, including bend and ovality.
 
4.1Bending degree 
The bending degree of steel pipe is divided into two types: full length bending degree and bending degree per meter.
 
1) The bending degree measured for the entire length of the steel pipe is called the full-length bending degree, and the full-length bending degree is divided into 5 levels.
   

Bending degree level	Full length bending degree,%
	≤
E1	0.20
E2	0.15
E3	0.10
E4	0.08
E5	0.06

 
 
2) Bend per meter
The degree of bending measured per meter of steel pipe is called the degree of bending per meter, and the degree of bending per meter is divided into 5 levels
 

Bending degree level	Bend per meter, mm / m
	≤
F1	3.0
F2	2.0
F3	1.5
F4	1.0
F5	0.5

 
 
4.2 Ovality
The ovality of the steel pipe is divided into 4 levels
 

Ovality level	Ovality is not greater than the allowable deviation of outer diameter,%
NR1	80
NR2	70
NR3	60
NR4	50

 
 
 
5. Weight
5.1Steel pipe weight requirements, steel pipes are delivered according to the actual weight, can also be delivered according to the theoretical weight. Actual weight delivery can be divided into single weight or batch weight.
The theoretical weight per meter of steel pipe is calculated according to the following formula:
W = 0.003.1416ρ (OD-WT)
In the formula:
W--theoretical weight of steel pipe, kg / m;
ρ—density of steel, kg / dm3;
OD—Nominal outer diameter of steel pipe, mm;
WT--Nominal wall thickness of steel pipe, mm.
 
For steel pipes delivered according to the theoretical weight, the allowable deviation between the theoretical weight and actual weight of a single steel pipe is divided into 5 levels.
   

Weight tolerance	Allowable deviation of single steel pipe weight,%
W1	±10
W2	±7.5
W3	+10 -5
W4	+10 -3.5
W5	+6.5 -3.5

 
 
5.2 The allowable deviation between the theoretical weight and actual weight of each batch of steel pipes not less than 10 tons is ± 7.5% or ± 5%.
 
 
 
6. What are the technical requirements for steel pipes for different purposes?
In general, according to the different uses of steel pipes and their working conditions, different technical conditions should be proposed for the allowable deviations in steel pipe size, surface quality, chemical composition, mechanical properties, process properties and other special properties.
 
1)Generally, when seamless steel pipes are used to transport various fluid pipes such as water, gas, and oil, and to manufacture various structural parts, the mechanical properties such as tensile strength, yield strength, and elongation should be sampled. Conveying pipes generally work under pressure, and require hydraulic tests and flaring, flattening, curling and other process performance tests. For large-scale long-distance crude oil, refined oil, and natural gas pipeline steel pipes, carbon equivalent, welding performance, low-temperature impact toughness, stress corrosion under severe corrosion conditions, corrosion fatigue, and strength under corrosive environments are added.
 
2)Boiler tubes are used to make superheated steam tubes and boiling water tubes for boilers of various structures. High pressure boiler tubes are used for superheated steam tubes for high pressure or ultra high pressure boilers, heat exchangers and pipes for high pressure equipment. The above-mentioned steel pipes for thermal equipment are operated under different high temperature and high pressure conditions, and good surface conditions, mechanical properties and process properties should be guaranteed. Generally, its mechanical properties are checked, and flattening and hydraulic tests are performed. High-pressure boiler tubes also require grain size inspection and stricter non-destructive testing.

3)Mechanical seamless steel pipes must have high dimensional accuracy, good mechanical properties and surface conditions according to application requirements. For example, the bearing tube requires higher abrasion resistance, uniform organization and strict inner and outer diameter tolerances. In addition to the general mechanical performance inspection items, low magnification, fracture, annealed structure (spheroidized structure, reticulated light, ribbon), non-metallic inclusions (oxides, sulfides, dots, etc.), Carbon layer and its hardness index.
 
4)Chemical fertilizer high-pressure seamless steel pipes are often used to transport chemical media (such as synthetic ammonia, methanol, urea, etc.) under a pressure of 2200 ~ 3200Mpa, an operating temperature of -40 ℃ ~ 400 ℃, and a corrosive environment. The high pressure seamless steel pipe for the fertilizer industry should have strong corrosion resistance, good surface condition and mechanical properties. In addition to mechanical performance, flattening and hydrostatic tests, corresponding simplified corrosion tests, managerial degrees and more stringent non-destructive tests should be performed according to different steel types.
 
5)Petroleum and geological drilling steel pipes work under the severe environment of high pressure, alternating stress and corrosiveness, so they should have a high strength level and be able to resist wear, torsion and corrosion. According to the different grades of steel, tensile strength, yield strength, elongation, impact toughness and hardness should be tested. For casings, tubing and drill pipes used in petroleum wells, steel grades and categories are divided in detail, as well as additional higher technical conditions applicable to different environments and geological conditions selected by users themselves to meet different special needs.
 
6)In addition to mechanical performance and hydraulic pressure tests, various stainless heat-resistant and acid-resistant pipes used in the chemical, petroleum cracking, aerospace, and other machinery industries are also specifically tested for intergranular corrosion tests, flattening, flaring, and nondestructive testing.