API 5L Welded Steel Pipe

API early in 1926 released by the American Petroleum Institute (API) API-5L standard, initially including three steel grade A25, A, B, and later released several times. API 5L welded steel pipe is mainly used for the delivery of the onshore and offshore oil and gas, coal slurry, the slurry media and offshore platforms, power plants, chemical industry and urban construction, structural tubes.

China is currently used in the Petroleum Pipeline tube spiral welded pipe (SSAW steel pipe), LSAW steel pipe, electric resistance welded pipe (ERW steel pipe). Diameter less than 152mm selection of seamless steel tubes. Of the late 1960s to the 1970s, spiral pipe plant rapid development of crude oil pipelines almost all spiral welded steel pipe. The spiral welded steel pipe of the disadvantage is the internal stress is large, the dimensional accuracy is poor, the probability of generation of defects. According to expert analysis, should adopt the policy of "walking on two legs", and actively carry out technological transformation now spiral welded pipe plant, also in promising; vigorously develop straight seam submerged arc control tube industry in China. ERW steel pipe with a smooth appearance, high dimensional accuracy, lower prices, and has been widely used at home and abroad.

Straight seam high frequency welded steel molding process that used in the production of LSAW steel pipe by Prime Steel Pipe is with advanced, reliable quality, welding position, stable welding parameters, welding speed, high yield, and the entire production line equipment and technology are world-class level.

(1) straight seam high frequency welded steel pipe forming process spring back small residual stress.
(2) the strain hardening effect is small, precise geometric dimensions full circle, will help ensure the quality of construction and welding.
(3) straight seam high frequency welded steel bead shape is good, not prone to biting edge, inside and outside the weld misalignment defects.
(4) straight-seam pipe weld distributed in a point on the circumference and, therefore, according to the demand to weld on a favorable position.

The Types of Rotary Contact Wheel Welding

Today, Prime Steel Pipe will share the type of rotary contact wheel welding for everyone. In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process. The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.

AC Rotary Contact Wheel Welding. In an AC rotary contact wheel welding machine, the current is transferred through the brushes to the rotating shaft, which has a transformer mounted on it. The transformer reduces the voltage and increases the current, making it suitable for welding. The two legs of the transformer's output circuit are connected to the two halves of the rotating contact wheel, which are insulated from each other. The strip completes the circuit by acting as a conductor between the two halves of the wheel.

Traditional rotary contact wheel welders used 60-hertz AC, or common line current. A drawback to this system is that the current--and therefore the weld heat--rises and falls, limiting the speed at which the tube can be welded. An AC sine wave reaches its maximum amplitude briefly, producing weld heat that varies just as the sine wave does.

To help even out the heat variation, motor generator sets were introduced to create AC at higher frequencies. Some of the frequencies used were 180, 360, 480, and 960 Hz. A few solid-state units also were produced to generate higher-frequency currents. An AC sine wave at 960 Hz reaches its maximum amplitude 1,920 times per second, as opposed to 120 times per second with a 60-Hz signal. The 960-Hz sine wave produces heat with a much more consistent temperature.

DC Rotary Contact Wheel Welding. The next step in rotary contact wheel welding was the DC power supply. The power produced has a nearly constant amplitude. Although this solves the problem of varying heat, a major drawback is that higher maintenance costs are associated with this type of welding machine.

Because it is not possible to change the voltage of DC with a transformer, it is necessary to transmit the high-amperage, low-voltage weld current into the shaft through a large number of brushes (92 for DC versus 8 for AC) with a high current density. Transmitting high-amperage, low-voltage current produces excess (waste) heat that causes heavy wear, resulting in the high maintenance costs mentioned previously.

Square Wave Rotary Contact Wheel Welding. The latest step in the evolution of rotary contact wheel welding is the square wave power supply. This method combines the consistent weld heat of DC with the lower maintenance associated with AC units.


The Types of Electric Resistance Welding

We knew what is electric resistance welding (ERW) previously, next, Prime Steel Pipe will continue to share the types of Electric Resistance Welding. We will discuss high-frequency ERW (contact and induction) and rotary wheel contact welding (AC, DC, and square wave). And we will share the differences among the processes, as well as the power supplies and weld rolls.

All ERW processes have one thing in common–all of them produce a forged weld, although each process has different characteristics. Several electric resistance welding (ERW) processes are available for ERW steel pipe production. The two main types of ERW are high-frequency (HF) and rotary contact wheel.

High-frequency (HF) Welding

The two main aspects of HF welding are processes and power supplies. The two HF welding processes are HF contact and HF induction. In both processes, the equipment that provides the electrical current is independent from the equipment that supplies the forge pressure. Also, both HF methods can employ impeders, which are soft magnetic components located inside the tube that help to focus the weld current in the strip edges. In the case of HF induction welding, the weld current is transmitted to the material through a work coil in front of the weld point. The work coil does not contact the tube--the electrical current is induced into the material through magnetic fields that surround the tube. HF induction welding eliminates contact marks and reduces the setup required when changing tube size. It also requires less maintenance than contact welding. HF contact welding transfers weld current to the material through contacts that ride on the strip. The weld power is applied directly to the tube, which makes this process more electrically efficient than HF induction welding. Because it is more efficient, it is well-suited to heavy-wall and large-diameter tube production. HF welding machines also are classified by how they generate power. The two types are vacuum tube and solid-state. The vacuum tube type is the traditional power supply.

Rotary Contact Wheel Welding

In rotary contact wheel welding, the electrical current is transmitted through a contact wheel at the weld point. The contact wheel also applies some of the forge pressure necessary for the welding process. The three main types of rotary contact wheel welders are AC, DC, and square wave. In all three power supplies, electrical current is transferred by brush assemblies that engage slip rings attached to a rotating shaft that supports the contact wheels. These contact wheels transfer the current to the strip edges.

Difference between Seamless Stainless Steel Pipe and ERW Stainless Steel Pipe

There are some customer don’t know how to distinguish the seamless stainless steel pipe and ERW stainless steel pipe. Today, Prime Steel Pipe will discuss about differences between seamless stainless pipe and ERW stainless steel pipe.

What is the raw material required for manufacturing seamless & ERW stainless steel Pipes? Seamless Steel Pipe is made from a solid round steel ‘billet’ which is heated and pushed or pulled over a form until the steel is shaped into a hollow tube. Billets are procured both from indigenous suppliers and from abroad. HR Coils are required to manufacture ERW stainless steel pipes.

How to Identify Seamless or ERW Stainless Steel pipes?

To identify that a pipe supplied is seamless or ERW, Simply read the stencil on the side of the pipe. If it is ASTM A53, Type S means seamless. Type F is furnace but welded, type E is Electrical resist welded.

What is the difference between seamless stainless steel pipe and ERW stainless steel pipe?

1. ERW steel pipe is manufactured by rolling metal and then welding it longitudinally across its length. Seamless pipe is manufactured by extruding the metal to the desired length; therefore ERW steel pipe have a welded joint in its cross-section, while seamless pipe does not have any joint in its cross-section through-out its length.

2. In Seamless steel pipe, there are no welding or joints and is manufactured from solid round billets. The seamless pipe is finished to dimensional and wall thickness specifications in sizes from 1/8 inch to 26 inch OD. Applicable in for High-pressure applications such as Hydrocarbon Industries & Refineries, Oil & Gas Exploration & Drilling, Oil & Gas Transportation and Air and Hydraulic cylinders, Bearings, Boilers, Automobiles, etc.

3. ERW steel pipes are welded longitudinally, manufactured from Strip / Coil and can be manufactured upto 24” OD. ERW steel pipe cold formed from a ribbon of steel pulled through a series of rollers and formed into a tube which is fused through a electric charge. It is mainly used for low/ medium pressure applications such as transportation of water / oil.

4. Common sizes for ERW Steel Pipe range from 2 3/8 inch OD to 24 inch OD in a variety of lengths to over 100 feet. Surface finishes are available in bare and coated formats and processing can be handled on site to customer specifications.

The Forming Speed of The Welded Steel Pipe Unit

The speed of the welded steel pipe unit is limited by the high-frequency welding speed. Generally speaking, the unit speed can be opened at a speed of 100 m/s, and the speed of the unit in the world is even 400 m/s Welding, especially in the induction welding can only be 60 meters/second or less, more than 10mm of steel plate molding, the domestic unit production molding speed can only reach 8 to 12 m/s. The welding speed affects the welding quality of welded steel pipe. When the welding speed is high, it will help to shorten the heat affected zone and facilitate the extrusion of the oxide layer from the molten groove. On the other hand, when the welding speed is very low, the heat affected zone becomes wider, resulting in a larger welding burr, , Weld quality deteriorated. Of course, the welding speed of welded steel pipe unit by the output power limit, it is impossible to mention very high. Domestic unit operating experience shows that 2 ~ 3 mm steel pipe welding speed can reach 40 m/s, 4 ~ 6mm steel pipe welding speed can reach 25 m/s, 6 ~ 8 mm welded steel pipe welding speed can reach 12 m/10 ~ 16 mm welded steel pipe welding speed of 12 m/s or less. Contact welding speed can be higher, induction welding will be lower.

Production Technology of SSAW Steel Pipe

SSAW steel pipe (some people call it spiral welded pipe) is also a kind of welded pipe, its strength is generally higher than the LSAW steel pipe. Spiral welded pipe with large diameter can be produced by the narrow blank, and SSAW steel pipe with different diameter can also be produced by the same width of blank. However, compared with the same length of the straight pipe, the weld length increased by 30 to 100%, and the production rate is low. Therefore, the smaller diameter of the pipe mostly use LSAW steel pipe, large diameter welded pipe mostly use spiral welded pipe.

The production process of SSAW steel pipe

SSAW steel pipe is the steel pipe with spiral seam that using the strip coil as raw material, extrusion forming under normal temperature, and using automatic double wire double-sided submerged arc welding process to weld.

1.Raw materials are coil, wire, flux. Those must finish the rigorous physical and chemical testing before putting into.
2.The head and tail of strip steel butt joint, use single or double wire submerged arc welding, and use automatic submerged arc welding to repair welding after rolled into steel pipe.
3.Before forming, the strip will go through the leveling, cutting edge, planing edge, surface cleaning and delivery to the edge of the treatment.
4.Using electrical contact pressure gauge control the pressure of the cylinder on both sides of the conveyor to ensure the smooth delivery of the strip.
5.Use external control or internal control roll forming.
6.Use weld gap control device to ensure that the weld gap to meet the welding requirements, diameter, misalignment and weld gap are strictly controlled.
7.Welding and external welding all use American Lincoln welding machine to single or double wire submerged arc weld, in order to obtain a stable welding specifications.
8.The welding line after welding must go through on-line continuous ultrasonic automatic injury inspection to ensure that 100% of the spiral weld non-destructive testing coverage. If there are defects, automatic alarm and spray marking, production workers adjust the process parameters at any time, eliminate of defects timely.
9.Use air plasma cutting machine to cut a single pipe.
10.After cutting into a single steel pipe, the first three of each batch of steel pipe must be carried out a strict first inspection system, to check the weld mechanical properties, chemical composition, melting conditions, steel pipe surface quality and after nondestructive testing to ensure that the pipe process qualified, so it can be put into formal production.
11.There are parts marked by ontinuous acoustic flaw on the seam, after manual ultrasound and X-ray review, if there are defects, after repair, again after the nondestructive test until the defect has been confirmed to eliminate.
12.The butt welds and helical welds of strip steel where the junction of the Ding-type joints, all through the X-ray TV or film inspection.
13.Each pipe must go through the hydrostatic test, the pressure using radial seal. Test pressure and time by the steel pipe hydraulic microcomputer detection device strictly controlled. Test parameters are automatically printed.
14.Pipe end machining, so that the vertical face, bevel angle and blunt edge to be accurately controlled.