Steel pipe pile foundation has the characteristics of quick construction, safety and highly mechanized operation, and is often widely used in large offshore bridges, substructures of ports and wharves, temporary platforms and trestles, etc. Compared with reinforced concrete foundation, steel tube pile foundation has the following advantages:

• Lightweight, high strength, convenient loading and transportation;
• High bearing capacity. The steel can be effectively driven into the hard soil and the pile body is not easy to damage and can obtain a great single pile bearing capacity;
• The length is easy to adjust, can be adjusted by connecting or cutting according to the need.
• A small amount of soil discharge. The lower end of the pile is open. With the driving of the pile, the soil squeezing volume of the pile pipe is greatly reduced compared with that of the solid core concrete pile, and the disturbance to the surrounding foundation is less and the displacement is less.
• It can be welded, easy to operate and fast to construct.

Steel pipe piles are generally made of plain carbon steel, with a tensile strength of 402MPa and yield strength of 235.2MPa, or according to the design requirements. It can be an SSAW pipe and an LSAW pipe. SSAW steel pipe has high rigidity and is commonly used. In order to facilitate transportation and be limited by pile frame height, steel pipe piles are usually composed of an upper section pile, a lower section pile and several middle section piles respectively. The length of each section is generally 13m or 15m, as shown in the figure:

A) Lower section pile;

(b) Mid-section pile;

(c) Upper section pile

The lower end of the steel pipe pile is divided into opening and closing. Its structure and type are shown in the figure below:

The diameter of the steel pipe pile is φ406.4-φ2032.0mm, and the wall thickness is 6-25mm.

We should take the engineering geology, load, foundation plane, upper load and construction conditions into consideration. Commonly used specifications are 406.4mm, 609.6mm and 914.4mm, wall thickness 10, 11, 12.7, 13mm, etc. Generally, upper, middle and lower section piles usually adopt the same wall thickness. Sometimes, in order to make the pile top bear the huge hammer impact and prevent the radial instability, the wall thickness of the upper section of the pile should be appropriately increased, or a flat steel reinforcement collar 200~300mm wide and 6~12mm thick should be added to the outer ring of the pile pipe. In order to reduce the friction resistance of the pile pipe sinking and prevent the end from being damaged due to deformation when penetration into the hard soil layer, a strengthening collar is also set at the lower end of the steel pipe pile. For Φ406.4 ~ Φ914.4mm steel pipe, the size of the strengthening pipe collar is 200~300mm*6~12mm.

(a) Structural forms of steel tube pile joints with different wall thicknesses;

(b) Reinforcement collar on top of piles;

(c) Reinforcement collar at the lower end of the pile

The accessories of steel pipe piles mainly include a pile cover welded on top of the pile for bearing the upper load, flat steel strip, a protective ring at the bottom of the pile, and a copper clamp welded on the pile joint. In order to reduce the negative friction of soft soil foundation on the bearing capacity of piles, a layer of special asphalt, polyethylene and other composite materials are coated on the outer surface of the upper end of the steel pipe pile to form a sliding layer of 6~10mm, reducing the negative friction by 4/5-9/10.

Structure of sliding layer of steel pipe pile:

1 Steel pipe pile;

2 Primer coating;

3 Sliding layer;

4 Surface

The strength of steel refers to the deformation and fracture performance of metal materials under the action of external force, which generally includes tensile strength, bending strength and compressive strength. The more resistant steel is to external forces, the stronger the steel will be. So how can we improve the strength of steel?

Solution Strengthening

The solid solution of alloying elements in the matrix metal causes certain lattice distortion and increases the strength of the alloy. Lattice distortion increases the resistance of dislocation movement and makes it difficult to slip, thus increasing the strength and hardness of the alloy solid solution. This phenomenon of strengthening a metal by dissolving into a solute element to form a solid solution is called solid solution strengthening.

The strength and hardness of the material are increased with the proper concentration of solute atoms, but the toughness and plasticity are decreased. The higher the atomic fraction of solute atom is, the greater the atomic size difference between solute atom and matrix metal is, and the stronger the strengthening is. 

The interstitial solute atoms have a greater solution strengthening effect than the substitutive atoms, and the strengthening effect of interstitial atoms is greater than that of face-centered cubic crystals because the lattice distortion of interstitial atoms in body-centered cubic crystals is asymmetric. However, the solid solubility of interstitial atoms is very limited and the actual strengthening effect is also limited. The larger the difference in the number of valence electrons between the solute atom and the substrate metal is, the more obvious the solution strengthening is, that is, the yield strength of the solid solution increases with the increase in the concentration of valence electrons.

Work Hardening

With the increase of cold deformation, the strength and hardness of metal materials increase, but the plasticity and toughness decrease. Cold work hardening is the phenomenon that the strength and hardness of metal materials increase while the plasticity and toughness decrease during plastic deformation below the recrystallization temperature. Because the metal in the plastic deformation, grain slip, dislocation causes grain elongation, fragmentation and fibrosis, the metal internal residual stress. Work hardening is usually expressed by the ratio of the microhardness of the surface layer after machining and before machining and the depth of the hardening layer.

Work hardening can improve the cutting performance of low carbon steel and make the chip easy to separate, but it brings difficulties to the further machining of metal parts. For example, in the process of the cold-rolled steel plate and cold-drawn steel wire, the energy consumption of drawing is increased and even is broken, so it must be through intermediate annealing to eliminate work hardening. In the cutting process to make the surface of the workpiece brittle and hard, increase the cutting force and accelerate tool weariness, etc.

It improves the strength, hardness and wear resistance of steels, especially for those pure metals and some alloys whose strength cannot be improved by heat treatment. Such as cold drawn high strength steel wire and cold coil spring, is the use of cold processing deformation to improve the strength and elastic limit. The track of tank, tractor, and the turnout of railway also use work hardening to improve its hardness and wear resistance.

Fine-grain Strengthening

The method of improving the mechanical properties of metal by refining grain is called fine grain strengthening. We know that a metal is a polycrystal composed of many grains, and the size of the grains can be expressed by the number of grains per unit volume. The more the number, the finer the grains. The experiments show that the fine grain metal has higher strength, hardness, plasticity and toughness than the coarse grain metal at normal temperature. This is because the fine grains can be dispersed in more grains when plastic deformation occurs under external force, so the plastic deformation is more uniform and the stress concentration is small.

In addition, the finer the grain is, the larger the grain boundary area is, and the more tortuous the grain boundary is, the more disadvantageous the crack propagation is. Therefore, the industrial method to improve the material strength by refining grain is called fine grain strengthening. The more grain boundaries are, the smaller the stress concentration is, and the higher the yield strength of the material is. Methods to refine the grain include: increasing the degree of supercooling;

Metamorphic treatment;

Vibration and agitation;

Cold-deformed metals can be refined by controlling the degree of deformation and annealing temperature.

Second Phase Strengthening

In addition to the matrix phase, the second phase exists in the multiphase alloy compared with the single-phase alloy. When the second phase is distributed uniformly in the matrix phase as finely dispersed particles, the strengthening effect will be significant. This strengthening is called second phase reinforcement. For the dislocation movement, the second phase of the alloy has the following two conditions: (1) reinforcement by an indeformable particle (a bypassing mechanism). (2) The strengthening effect of deformable particles (a cutting mechanism).

The dispersion strengthening and precipitation strengthening both belong to the special cases of the second phase strengthening. The main reason for the strengthening of the second phase is the interaction between them and the dislocation, which hinders the dislocation motion and increases the deformation resistance of the alloy.

In general, the most important thing that affects the strength is the composition of the metal itself, the organizational structure and the surface state, followed by the stress state, such as the speed of the after force, the loading method, the simple stretching or repeated stress, they will show different strength; In addition, the shape and size of the metal and the test medium also have an effect, sometimes even decisive, such as the tensile strength of ultra high strength steels may be reduced exponentially in a hydrogen atmosphere.

There are two main ways to improve the strength: one is to improve the interatomic bonding force of the alloy to improve its theoretical strength, and to produce a complete crystal without defects such as whiskers. The strength of the known iron whiskers is close to the theoretical value, which can be assumed to be due to the lack of dislocations in the whiskers or to the fact that they contain only a small number of dislocations that cannot proliferate during deformation. However, when the diameter of the whisker is large, the strength will decrease sharply. Secondly, a large number of crystal defects are introduced into the crystal, such as dislocation, point defects, heterogeneous atoms, grain boundaries, highly dispersed particles or inhomogeneity (such as segregation), etc. These defects hinder the dislocation movement and significantly improve the metal strength. This proved to be the most effective way to increase the strength of the metal.

Line pipe is a type of steel pipe that is used for transporting materials through pipelines across the country. Line pipe can be used to transport petroleum, natural gas, oil, and water. It is a durable pipe that must meet certain specifications and regulations. This pipe typically has a high strength and durability in order to withstand high pressures. At Wldsteel, we sell and distribute line pipe in a complete variety of sizes, lengths, diameters, and grades.

To learn more about our line pipe sales and distribution services or to receive a quote for your specific requirements, please

What is Line Pipe
Line pipe is a type of pipe that is manufactured from high strength carbon steel. It is typically made according to metallurgical specifications that were developed by the American Petroleum Institute (API). Line pipe can be used to build pipelines that transport a variety of resources including natural gas, oil, petroleum, and water. This pipe is available in a variety of diameters ranging from 2 inches to 48 inches. Line pipe can include either seamless or welded carbon steel or stainless steel piping. Because line pipe needs to withstand high pressures, there are important tests done on line pipe to ensure it meets all of the requirements of steel chemistry, strength, toughness, and dimensional characteristics. Using line pipe that meets the set criteria will ensure safe and reliable pipeline service.

The size and diameter of line pipe that is required for a pipeline can vary based on the amount of gas or liquid that a pipe is intended to carry as well as the pressures that a line pipe must withstand. For example, in most cases a mainline, the principal pipeline that delivers natural gas, will require line pipe that is around 16 to 48 inches in diameter. Smaller pipelines that deliver gas to the mainline or take gas from a mainline can be constructed of 6 to 16 inch diameter line pipe. One can determine the necessary diameter required for a pipeline by considering the volume of gas or liquid that the line pipe will be carrying as well as the pressure at which this will be transported.

The thickness requirements for line pipe are determined by the maximum operating pressure required for a pipeline. This is based on published standards and federal regulations. Following proper safety regulations when selecting and installing line pipe, will ensure proper pipeline operation and prevent dangerous or hazardous situations.

Buy Line Pipe
At Wldsteel, we sell carbon steel line pipe and  stainless steel pipe in a variety of sizes, diameters, and thicknesses. This line pipe can be used for pipelines that carry oil, petroleum, natural gas, or water. Most sizes of our ERW, DSAW and Seamless Steel pipe are available with mill test reports and full traceability as required. We can supply many grades of line pipe, including API 5L-B, X-42, X-46, X-52, X-60, X-70 and higher.

As a leading pipe distributor, we are not only able to supply new line pipe direct from stock or mill sources, but we can also cut pipe to your required length and add special coatings as needed. We can deliver line pipe and other stainless steel piping to nearly any worksite or location throughout the United States. To learn about our current selection of line pipe for sale or to learn more about our stainless steel pipe distribution services, please feel free to contact us at WLD Steel.