What are differences between STC, LTC and BTC in OCTG casing pipe?

What are differences between STC, LTC and BTC in OCTG casing pipe?

What are differences between STC, LTC and BTC in OCTG casing pipe?

Common threads of OCTG casing pipe can be divided into three kinds: STC, LTC, and BTC. STC is short for short-round thread casing, LTC long-round thread casing, BTC buttress thread casing. There are three specified lengths of API LTC casing: R-1 is 4.88 ~ 7.62m, R-2 is 7.62 ~ 10.36m, and R-3 is 10.36m to longer. The main steel grades: H-40, J-55, K-55, N-80, C-75, L-80, C-90, C-95, P-110 and Q-125. According to different well conditions and different well depth, different steel grade is selected. The corrosion resistance of the casing itself is also required in the corrosive environment. API oil casing ring parts made of steel pipe can improve material utilization, simplify manufacturing process and save material and processing time. Due to the harsh geological conditions, higher requirements are put forward for mechanical properties such as tensile properties and compressive properties of the tube body. properties testing for hydrostatic test, flattening test, sulfide stress corrosion cracking test, hardness test, tensile test, and horizontal impact test. In the complex geological conditions, the casing is also required to be resistant to extrusion.




Features of STC :

  1. Improve the resistance caused by scratch during screw tightening
  2. When screwed up, the crown clearance provides a controlled clearance for foreign particles and dirt
  3. The rounded crown is not sensitive to local scratches or dents.

The quality of the threaded connection directly affects the structural integrity and sealing integrity of the casing string, and the machining accuracy of the threaded connection is one of the important factors.



The thread shape of both ends of the pipe body is like long round, so it is called long round thread casing. Long round thread has the advantages of easy machining, good sealing, certain connection strength, simple field maintenance and use, cheap price, etc., and is widely used in casing connection.




BTC-buttress thread casing

Buttress thread casing pipe is named according to thread shape which is partial trapezoid, and it is one of the commonly used buckle shapes.

The advantage of BTC: improves the axial tensile and axial compression load resistance and provides leakage resistance.

IMRISTEEL can fabricate STC, LTC and BTC according to API 5CT, what’s more, our factory also can produce BT-1, BT-2 and BT-3 which can substitute for special thread, such as New VAM and VAM top.


Characteristics and application of hot rolled seamless steel pipes and cold drawn seamless steel pipes

Characteristics and application of hot rolled seamless steel pipes and cold drawn seamless steel pipes

Seamless steel pipes are divided into hot rolled and cold rolled (drawn) seamless steel pipes.


Cold-rolled seamless steel pipes:

Cold-rolled seamless pipes are used for mechanical structure, hydraulic equipment with high dimensional accuracy and good surface finish.


In addition to general steel pipes, low and medium pressure boiler steel pipes, high pressure boiler steel pipes, alloy steel pipes, stainless steel pipes, petroleum cracking pipes, also includes thin-wall carbon steel pipes,thin-wall alloyed steel pipes, thin-wall stainless steel pipes, special-shaped steel pipes.The outer diameter of hot-rolled seamless pipes is generally bigger than 32mm, the wall thickness is 2.5-75mm, the diameter of cold-rolled seamless pipe can be up to 6mm, the wall thickness can be up to 0.25mm, the outer diameter of thin-walled pipe can be up to 5mm, the wall thickness is less than 0.25mm, and the dimension precision of cold-rolled pipe is higher than hot-rolled pipe.


Hot rolled seamless steel pipes:

Hot rolled seamless steel pipes are divided into general steel pipes, low and medium pressure boiler tubes, high pressure boiler tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, geological steel tubes and other steel tubes.


General seamless tube: it is made of high quality carbon bonded steel such as 10,20, 30, 35 and 45. 16Mn, 5MwV and other low alloy structural steel, or alloy steel such as 40Cr, 30CiMnSi, 4512 and 40MnB. Hot rolled or cold rolled 10, 20 and other low carbon steel manufacturing seamless pipes are mainly used for fluid transport pipelines.Seamless pipes made of medium carbon steel such as 45 and 40Cr are used to make mechanical parts, such as stressed parts for cars and tractors.We need to ensure the strength and flattening test of generally used seamless steel tubes .Hot rolled steel tubes are delivered in hot rolled or heat treated state.Cold rolled steel pipes are delivered in heat treatment condition.

Characteristics and application of hot rolled seamless steel pipes and cold drawn seamless steel pipes

Main differences between hot rolled and cold rolled seamless tubes:


  1. Local buckling is allowed in the section of cold-rolled steel pipes, which can make full use of the bearing capacity of the pipes after buckling;However, local buckling of section is not allowed in hot rolled section.
  2. The causes of residual stress of hot rolled section and cold rolled section are different, so the distribution on the section is also very different.The residual stress distribution on the section of cold-formed thin-walled steel is of bending type, while that on the section of hot-formed steel or welded steel is of thin film type.
  3. The free torsional stiffness of hot-rolled sections is higher than that of cold-rolled sections, so the torsional resistance of hot-rolled sections is better than that of cold-rolled sections.

Cold rolled seamless tube is at room temperature, after cold drawing, cold bending and other cold processing,making steel plate or steel strip into a variety of steel tubes.


Advantages of cold rolled seamless steel pipes:

Fast molding speed, high yield, and no damage to the coating, can be made into a variety of cross section forms, to meet the needs of the use conditions;Cold rolling can produce a lot of plastic deformation of steel, thus increasing the yield point of steel.



Advantages of hot-rolled seamless steel pipes:

Compared with the cold rolled seamless tube, which is rolled below the recrystallization temperature,the hot rolled seamless tube is rolled above the recrystallization temperature. It can destroy the casting structure of steel ingot, refine the grain of steel, and eliminate the defects of microstructure, so that the microstructure of steel can be compactness and mechanical properties can be improved.This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to some extent.Bubbles, cracks and looseness formed during pouring can also be welded under high temperature and pressure.


What is calcined kaolin?

Kaolin is a mixture of inorganic non-metals.

Compared with uncalcined kaolin, calcined kaolin has less bound water content, increased silica and alumina content, increased active points, changed structure, smaller and uniform particle size, and is filled with uncalcined kaolin. Compared with the NR compound, the vulcanization characteristic curve of the low-temperature calcined kaolin filled NR compound is basically the same. The hardness of Sauer A type is unchanged and the tensile strength is improved. The physical properties of both meet the requirements of the sports shoe non-transparent sole industry standard.

The calcination process of kaolin

The production process of ultra-fine calcined kaolin mainly includes four parts: ① pre-drying of raw materials to meet the moisture requirements for ultra-fine pulverization; ② ultra-fine pulverization and classification of kaolin to achieve the required particle size for calcination; ③ high-temperature calcination to achieve the required purity Harmony whiteness; ④ After calcination, break up and disaggregate to reach the required fineness of the final product. The production process flow chart is as follows.

Paint coating, plastic and rubber grade: Kaolin raw material→water washing and impurity removal→mixing of chemicals→dry pulverization (800 mesh, 1250 mesh)→calcining→depolymerization and disintegration→product (800 mesh, 1250 mesh, 2000 mesh, 3000 mesh).

Papermaking coating grade: raw material→water washing and impurity removal→mixing of chemicals→dry grinding (2μm>80%)→calcining→mixing of dry grinding aids→depolymerization and dispersing→products (1250 mesh, 200 mesh, 3000 mesh, 2μm>70 %, 2μm>80% and some 2μm>90%).

What does MFR refer to ? Is it the bigger, the better the performance will be ?

What does MFR refer to ? Is it the bigger, the better the performance will be ?

What does MFR refer to ? Is it the bigger, the better the performance will be ?


What is MFR ?

Melt flow rate (short for MFR) is a parameter to describe the melt flow of plastics under certain temperature and pressure. At the same time, it also indirectly describes the average molecular weight of plastic weight. The melt index is commonly expressed by MI and is now internationally known as melt flow rate and is expressed by MFR. It is usually used as a parameter of thermoplastic resin quality control and thermoplastic molding process conditions. It is the weight value in grams per 10 minutes of thermoplastic resins and plastics that melt through standard capillaries over a specified period of time at a specified temperature and constant load. The melting index is used to distinguish the fluidity of various thermoplastic materials in the melting state.


How to measure MFR ?

FIG. 1 is a test machine, and FIG.2  is a schematic diagram of melt flow rate test.

The material sheet is wrapped with a heater. At the bottom of the barrel, there is an orifice die. The center of the orifice die is the capillary tube that the melt extrusion flows out.

A piston rod is inserted into the barrel and a weight is pressed on the top of the rod.

During the test, the cylinder is heated first, and after reaching the expected test temperature, the piston rod is pulled out and the sample plastic particles or powder are poured into the central hole of the cylinder.) After the tool is compressed, the piston rod is put into the cylinder, and the sample is melted, and a weight is pressed on the top of the piston rod. The molten sample material is extruded through the orifice mold capillary.










                          FIG. 1                                                                                                               FIG. 2


Whats the meaning of MFR ?

The melt flow rate characterizes the melt flow performance of the thermoplastic polymer. By measuring the melt flow rate, we can understand the polymer’s molecular weight and its distribution, degree of cross-linking, machining performance, etc.

For the same resin, the melt index can be used to compare the molecular weight of the resin for production quality control.Generally speaking, the chemical structure of a certain resin, its melting index is smaller, the greater the molecular weight, then its fracture strength, hardness, toughness, aging resistance stability and other properties have been improved. And melt index is big, molecular weight is small, the fluidity when molding is corresponding some better.

Welcome to contact us for more information of all kinds of plastic resins.

Specifications and usages of API 5CT petroleum tubing with the steel grades of J55 K55 N80 L80 C90 P110

Specifications and usages of API 5CT petroleum tubing with the steel grades of J55 K55 N80 L80 C90 P110


Tubing can be divided into flat tubing (NU), thickened tubing (EU) and integrated joint tubing.Flat tubing means the end of the tubing is threaded without being thickened and is fitted with a coupling.The thickened tubing means that after the two ends of the tubing are thickened externally, they are threaded and coupled with a coupling.The whole joint tubing means that one end is internally thickened before externally threaded and the other end is externally thickened before internally threaded, which is directly connected without a coupling.

Specifications and usages of API 5CT petroleum tubing with the steel grades of J55 K55 N80 L80 C90 P110

Usages of tubing:

1.oil and gas extraction: after the oil and gas well has been completed and cemented, the tubing is placed in the casing of the oil layer to pump oil and gas to the surface.

2.Water injection: when the downhole pressure is not enough, inject water into the well through the tubing.

3.Steam injection: In the process of heavy oil thermal recovery, heat insulation tubing should be used to input steam underground.

4.Acidizing and fracturing: to increase the production of oil and gas wells at the later stage of well drilling or in the future, it is necessary to input acidizing and fracturing media or solidified substances into the oil and gas reservoirs. Both media and solidified substances are transported through tubing.

Specifications of Commomly Used API 5CT Tubing
Inch NU EUE In. mm In. mm
1.9 2.4 1.9 48.26 0.125 3.18
2.75 2.9 1.9 48.26 0.144 3.68
3.65 3.73 1.9 48.26 0.2 5.08
4.42 1.9 48.26 0.25 6.35
5.15 1.9 48.26 0.3 7.62
2.063 3.24 2.063 52.4 0.156 3.96
4.5 2.063 52.4 0.225 5.72
2 3/8 4 2.375 60.32 0.167 4.24
4.6 4.7 2.375 60.32 0.19 4.83
5.8 5.95 2.375 60.32 0.254 6.45
6.6 2.375 60.32 0.295 7.49
7.35 7.45 2.375 60.32 0.336 8.53
2 7/8 6.4 6.5 2.875 73.02 0.217 5.51
7.8 7.9 2.875 73.02 0.276 7.01
8.6 8.7 2.875 73.02 0.308 7.82
9.35 9.45 2.875 73.02 0.34 8.64
10.5 2.875 73.02 0.392 9.96
11.5 2.875 73.02 0.44 11.18
3 1/2 7.7 3.5 88.9 0.216 5.49
9.2 9.3 3.5 88.9 0.254 6.45
10.2 3.5 88.9 0.289 7.34
12.7 12.95 3.5 88.9 0.375 9.52
14.3 3.5 88.9 0.43 10.92
15.5 3.5 88.9 0.476 12.09
17 3.5 88.9 0.53 13.46
4 9.5 4 101.6 0.226 5.74
10.7 11 4 101.6 0.258 6.55
13.2 4 101.6 0.33 8.38
16.1 4 101.6 0.415 10.54
18.9 4 101.6 0.5 12.7
22.2 4 101.6 0.61 15.49
4 1/2 12.6 18.97 4.5 114.3 0.271 6.88
15.2 4.5 114.3 0.337 8.56
17 4.5 114.3 0.38 9.65
18.9 4.5 114.3 0.43 10.92
21.5 4.5 114.3 0.5 12.7
23.7 4.5 114.3 0.56 14.22
26.1 4.5 114.3 0.63 16

Steel grades of tubing:

Steel grades of tubing are: H40, J55 and N80, L80, C90, T95, P110. N80 is divided into N80Q and N80-1, similarities of the two are the tensile properties,differences are the delivery status and impact performance, according to the state of normalizing delivery or N80-1 when the Ar3 finishing temperature is greater than the critical temperature and tension after reducing air cooling.It can also be replaced by hot rolling, and neither impact work nor non-destructive testing is required :N80Q must undergo tempering (quenching and tempering) heat treatment, impact work should comply with API 5CT regulations, and non-destructive testing should be conducted.

L80 is divided into L80-1, L80-9CR and L80-13CR, and their mechanical properties and delivery state are the same. The difference is in usage, production difficulty and price. L80-1 is a common type, L80-9CR and L80-13CR are both highly corrosion-resistant tubing, which is difficult to produce and expensive, and is usually used in heavily corrosion-resistant oil wells.

Want to know more about API 5CT tubings?Just contact us.


What is the use of kaolin?

KAOLIN has a wide range of uses. It is mainly used in papermaking, ceramics and refractory materials, followed by coatings, rubber fillers, enamel glazes and white cement raw materials, and a small amount is used in plastics, paints, pigments, grinding wheels, pencils, Daily cosmetics, soap, pesticides, medicine, textiles, petroleum, chemicals, building materials, national defense and other industrial sectors.


Process characteristics of kaolin:


Whiteness is one of the main parameters of kaolin process performance. Kaolin with high purity is white. The whiteness of kaolin is divided into natural whiteness and whiteness after calcination. For ceramic raw materials, the whiteness after calcining is more important. The higher the calcining whiteness, the better the quality. Ceramic technology stipulates that drying at 105°C is the classification standard for natural whiteness, and calcination at 1300°C is the classification standard for calcining whiteness. The whiteness can be measured with a whiteness meter. The whiteness meter is a device that measures the reflectance of light with a wavelength of 3800-7000 angstroms; (that is, angstroms, 1 angstrom = 0.1 nanometers). In the whiteness meter, compare the reflectance of the sample to be tested with the standard sample (such as BaSO4, MgO, etc.), that is, the whiteness value (for example, a whiteness of 90 means 90% of the reflectance of the standard sample).

Brightness is a process property similar to whiteness, equivalent to 4570 angstroms; (angstroms) whiteness under irradiation of wavelength light.

The color of kaolin is mainly related to the metal oxide or organic matter it contains. Generally, Fe2O3 is rose red and brownish yellow; Fe2+ is light blue and light green; MnO2 is light brown; organic matter is light yellow, gray, blue, black and other colors. The presence of these impurities reduces the natural whiteness of kaolin. Among them, iron and titanium minerals will also affect the whiteness of calcination, causing stains or melting scars on porcelain.

Particle size distribution

The particle size distribution refers to the proportion (expressed as a percentage) of the particles in the natural kaolin in a given continuous range of different particle sizes (expressed by the mesh of millimeters or micrometers). The particle size distribution characteristics of kaolin are of great significance to the selectability of ore and process applications. Its particle size has a great influence on its plasticity, mud viscosity, ion exchange capacity, molding performance, drying performance, and firing performance. Kaolin mines require technical processing, and whether it is easy to process to the fineness required by the process has become one of the criteria for evaluating the quality of the ore. Various industrial sectors have specific requirements for particle size and fineness of kaolin for different purposes. For example, the United States requires 90-95% of kaolin used as coatings with a content of less than 2μm, and 78-80% of paper fillers less than 2μm.


The mud formed by the combination of kaolin and water can be deformed under the action of external force. After the external force is removed, it can still maintain this deformation property, which is plasticity. Plasticity is the basis of the molding process of kaolin in the ceramic body, and it is also the main technological index. Plasticity index and plasticity index are usually used to express the size of plasticity. The plasticity index refers to the liquid limit water content of the kaolin clay minus the plastic limit water content, expressed as a percentage, that is, W plasticity index = 100 (W liquid limit-W plastic limit). The plasticity index represents the molding performance of kaolin clay. It can be obtained by directly measuring the load and deformation of the clay ball when it is crushed under pressure with a plasticizer. It is expressed in kg·cm. The higher the plasticity index, the better the molding performance. The plasticity of kaolin can be divided into four levels.

Plasticity Strength Plasticity Index Plasticity Index

Strong plasticity>153.6

Medium plasticity 7-152.5-3.6

Weak plasticity 1-7<2.5

Non-plasticity <1


Combination refers to the combination of kaolin and non-plastic raw materials to form a plastic mud mass and have certain dry strength properties. The binding capacity is determined by adding standard quartz sand to kaolin (its mass composition is 0.25-0.15 grain size accounting for 70%, and 0.15-0.09mm grain size accounting for 30%). The maximum sand content and the flexural strength after drying can be used to judge its height. The more sand mixed, the stronger the binding capacity of this kaolin. Generally, kaolin with strong plasticity has strong binding capacity.


Viscosity refers to a feature that hinders the relative flow of the fluid due to internal friction. The viscosity is used to express its size (the internal friction acting on a unit area), and the unit is Pa·s. Viscosity is generally measured by a rotational viscometer, measured by the rotational speed in a kaolin mud containing 70% solid content. In the production process, viscosity is of great significance. It is not only an important parameter of the ceramic industry, but also has a great impact on the paper industry. According to data, when kaolin is used as coating in foreign countries, the viscosity is about 0.5 Pa·s for low-speed coating and less than 1.5 Pa·s for high-speed coating.

Thixotropy refers to the characteristic that the mud that has been thickened into a gel and no longer flows becomes fluid after being stressed, and then gradually thickens into its original state after being stationary. The size is expressed by the thickening coefficient, and measured by an outflow viscometer and a capillary viscometer.

Viscosity and thixotropy are related to the mineral composition, particle size and cation type in the mud. Generally, the content of montmorillonite is high, the particles are fine, the exchangeable cations are mainly sodium, and its viscosity and thickening coefficient are high. Therefore, in the process, methods such as adding strong plastic clay and increasing the fineness are commonly used to increase its viscosity and thixotropy, and to reduce it by increasing diluted electrolyte and moisture.

Drying performance

Drying performance refers to the performance of the kaolin clay in the drying process. Including drying shrinkage, drying strength and drying sensitivity.

Drying shrinkage refers to the shrinkage of kaolin clay after drying without water. Kaolin mud is generally dehydrated and dried at a temperature of 40-60°C up to 110°C. Due to the discharge of water, the distance between particles is shortened, and the length and volume of the sample will shrink. Drying shrinkage is divided into line shrinkage and body shrinkage, expressed as the percentage change of the length and volume of the kaolin mud after drying to constant weight. The drying line shrinkage of kaolin is generally 3-10%. The finer the particle size, the larger the specific surface area, the better the plasticity, and the greater the drying shrinkage. The same type of kaolin shrinks differently due to different blending water, and more shrinkage. In the ceramic process, the drying shrinkage is too large, and the green body is prone to deformation or cracking.

Dry strength refers to the flexural strength of the mud after drying to constant weight.

Drying sensitivity refers to the degree of difficulty with which the green body may deform and crack when it is dried. High sensitivity, easy to deform and crack during the drying process. Generally, kaolin with high drying sensitivity (drying sensitivity coefficient K>2) is easy to form defects; the lower one (drying sensitivity coefficient K<1) is safer during drying.


Sinterability refers to the ability of the formed solid powdery kaolin body to be heated to close to its melting point (generally more than 1000°C), the material spontaneously fills the gap between the grains to densify. The state where the porosity drops to the minimum and the density reaches the maximum is called the sintering state, and the corresponding temperature is called the sintering temperature. When heating continues, the liquid phase in the sample increases and the sample begins to deform. The temperature at this time is called the transformation temperature. The interval between the sintering temperature and the conversion temperature is called the sintering range. The sintering temperature and sintering range are important parameters for determining the blank formulation and choosing the type of furnace in the ceramic industry. The sample is suitable for low sintering temperature and wide sintering range (100-150℃). In the process, the sintering temperature and sintering range can be controlled by mixing flux materials and mixing different types of kaolin in proportion.

Firing shrinkage

Firing shrinkage refers to a series of physical and chemical changes (dehydration, decomposition, formation of mullite, melting of fusible impurities to form a glass phase filling the voids between the particles, etc.) during the firing process of the dried kaolin blank , And the properties that cause product shrinkage are also divided into two types: linear shrinkage and body shrinkage. Like the drying shrinkage, the firing shrinkage is too large, which will easily cause the green body to crack. In addition, during firing, if a large amount of quartz is mixed in the billet, it will undergo a crystal transformation (three-sided → six-sided), which will cause its volume to expand and reverse shrinkage.

Fire resistance

Fire resistance refers to the ability of kaolin to resist high temperatures without melting. The temperature at which it softens and begins to melt under high temperature operation is called refractoriness. It can be directly measured using standard temperature measuring cones or high-temperature microscopy, or calculated using M.A Bezbelov’s empirical formula.

Refractoriness t (℃)=[360+Al2O3-R2O]/0.228

In the formula: Al2O3 is the mass percentage of Al2O3 when the sum of SiO2 and Al2O3 analysis results is 100; R2O is the mass percentage of other oxides when the sum of SiO2 and Al2O3 analysis results is 100.

The error of calculating the refractoriness by this formula is within 50℃.

The refractoriness is related to the chemical composition of kaolin. The refractoriness of pure kaolin is generally around 1700℃. When the content of hydromica and feldspar is high, and the content of potassium, sodium, and iron is high, the refractoriness will decrease. 1500°C. The industrial sector stipulates that the R2O content of refractory materials is less than 1.5-2%, and Fe2O3 is less than 3%.


Suspension and dispersibility refer to the property of kaolin that is difficult to settle when dispersed in water. Also known as anti-flocculation. Generally, the finer the particle size, the better the suspension. Kaolin used in the enamel industry requires good suspension. Generally, the suspension performance of the sample dispersed in water is determined by the sedimentation speed of a certain period of time.


Optionality means that kaolin ore is manually selected, mechanically processed and chemically treated to remove harmful impurities and make the quality meet the performance required by the industry. The selectivity of kaolin depends on the mineral composition, occurrence state and particle size of harmful impurities. Quartz, feldspar, mica, iron and titanium minerals are all harmful impurities. Kaolin beneficiation mainly includes projects such as sand removal, iron removal, and sulfur removal.


Kaolin has the ability to adsorb various ions and impurities from the surrounding medium, and has weak ion exchange properties in the solution. The pros and cons of these properties mainly depend on the main mineral components of kaolin, and the cation exchange capacity of different types of kaolin.

Features of mineral composition Cation exchange capacity

Kaolinite is mainly 2-5mg/100g

Halloysite-based 13mg/100g

Contains organic matter (ball soil) 10-120mg/100g

Chemically stable

Kaolin has strong acid resistance, but its alkali resistance is poor. Use this property to use it to synthesize molecular sieves.

Electrical insulation

High-quality kaolin has good electrical insulation, and it can be used to make high-frequency porcelain and wireless porcelain by using this property. The level of electrical insulation performance can be measured by its resistance to electrical breakdown.