Seamless pipe vs Welded pipe

A Seamless steel pipe is extruded and drawn from a billet whereas a welded pipe is produced from a strip that is roll formed and welded to produce a pipe.

Concentricity: seamless pipe manufacturing process is at a temperature of 2200 ° F in a stainless steel billet punching out a hole in this high temperature tool steel by stamping and drawing becomes soft and spirally from the Kong Zhongcheng shaped out. Such uneven wall thickness of the pipe and the eccentric high.

Thus ASTM standard allow the wall thickness difference of seamless pipes is bigger than the welded pipes'. Slotted tube is made by precision cold-rolled plates (4-5 feet) per roll width. These cold rolled sheet is usually the maximum wall thickness of 0.002 inches. The steel sheet was cut to the width πd where d is the outer diameter of the pipe. Slit pipe wall thickness tolerances are small, and the entire circumference of the wall thickness is very uniform.

Welding performance: general tube and seamless pipe has certain differences on the chemical composition. The production of seamless pipe steel composition is only the basic requirements to meet ASTM. While the production of the chemical composition of the steel slotted tube containing suitable for welding. For example, silicon, sulfur, manganese, oxygen and the triangle of ferrite and other elements at a certain proportion of mixed can be generated during the soldering process the solder melting and an easy transfer of heat, so that the entire weld penetration. Lack of the above chemical composition of the steel pipe, such as seamless tubes, in the welding process will produce a variety of factors of instability, is not easy to weld and welding impervious.

Grain size: Typically, Metal grain size and heat treatment temperature and keep the same temperature is related with the time. Therefore, the annealed the same seam pipe and seamless pipe grain size. If there is a seam tube with a minimum of cold treatment, the grain size of the weld seam is less than the grain size of the weld metal, otherwise, the grain size is the same.

Strength: the strength of the pipeline depends on the alloy composition, and thus contain the same alloy and the same heat treatment of seamless pipe and slotted tube essentially are consistent strength. After tensile testing and three-dimensional vibration test, slotted tube tear occur almost exclusively in a place away from the welding point or heated area. This is because fewer impurities and a slightly higher nitrogen content of the weld, and thus the strength of the weld at better than the other region. However, the ASME Boiler and Pressure Vessel Association seam pipe can only bear 85% of the allowable pressure, which is mainly due to the data collected as early as today has improved welding equipment. ASME regulations 100% seam tube can withstand the allowable pressure by ultrasonic testing. Similarly, Europe and Asia also provides seam pipe to ensure the quality of its welding performance by means of eddy current testing, eddy current testing require the approval of the legal procedures and licenses held by institutions. Trent eddy current testing by the permission of the Swedish Ministry of Power. ASME small current loss is based on the quality performance of the slotted tube.

Corrosion resistance: good or bad corrosion resistance also depends on the composition of the alloy. Full heat treatment of a seamless pipe with the same chemical composition and by the corrosion resistance of the slit pipe is consistent. The ASTM provides supplementary tests proved weld corrosion resistance equal to or better than the metal being welded. In acidic chloride environment, not fully heat at the welding of the slit pipe corrosion will be accelerated, but only the needs of the corrosion test, in fact, the environment is not so bad. Bending and extension: the extension of the welding prescribed by ASTM following tests to verify: bent 45 ° bent to 90 °, flattened along the weld; then turned the seam pipe Repeat the above steps to make the weld The curved inner diameter is 180 °. Weld quality by the standards is not allowed to appear in the case of 40-fold magnification tear or intergranular separation. Pipe bending radius is controlled by the composition of the alloy, the general minimum bend radius of 2D.

The ideal welding condition is a seam in a neutral or compressed state. Moreover, the pipes should be an annealing treatment in order to reduce its hardness, thereby improving the bending performance.


Advantages of Welded Steel Pipe

Welded pipe is made by cold forming flat strip, sheet or plates into a round or circular shape by a roller or plate bending machine. The pipe is then welded with or without filler material using a high energy source. Welded pipes can be produced in large sizes without any size restriction. Welded pipes are normally used for transportation of water, oil or gases in large quantities.

Welded steel pipes are always available in plenty because of their lower production cost and raw materials availability. It is, therefore, one of the most widely used metals in the world. Its application in different industries and the manufacture of numerous products. Examples of ASTM or API 5L welded steel pipes include SSAW pipe, ERW steel pipe, and LSAW pipe.

Many people confuse the ERW pipe with seamless steel because it does not use fusion metals, the weld seam is not always visible, and you cannot feel it. On the contrary, a Double Submerged Arc Weld (DSAW) leaves evident traces of weld beads, which can be eliminated using different processes depending on the application method.

Applications

Welded steel pipes are widely used in several industries because they are cost-effective. They can also be manufactured in different lengths and welded from different tubing shapes. Application is entirely dependent on the use and other related factors.

The following are some of the areas of application:


Advantages of Seamless Steel Pipe

A seamless steel pipe is made of a single piece of metal, and it does not have a jointed steel pipe on the surface. As its name suggests, seamless steel pipe does not have a seam (crease) or a welded joint.

Seamless pipe is made from a round steel billet (solid cylindrical hunk of steel that is cast from raw steel). This billet is then heated, stretched out and pushed or pulled over a form. It is then pierced through the center with a die and mandrel which increases the inside diameter and reduces the outside diameter. Even though seamless pipes are manufactured in a variety of sizes, with an increase in pipe diameter the production cost increases. The name seamless comes from its absence of a seam. Seamless pipes are widely used in process piping, power piping, shipbuilding, pressure vessel, construction, and chemical industries.

Applications

Seamless steel pipes use specific applications because of their unique properties such as uniform strength distribution, non-welded joints, and their ability to withstand high temperatures, pressure capacity, high quality, better weight limit, and many more.

The following are some areas of application that use specifically seamless steel pipes:


Seamless vs Welded Pipe

From the above paragraphs, it is obvious that seamless and welded pipes differ in their manufacturing process. The other differences are listed in the below-attached table.

Table explaining differences between Seamless and Welded Pipes

Sr. No Parameter Seamless Pipe Welded Pipe
1 Strength Able to withstand more pressure and load as there is no weak seam. Due to welding they are believed to withstand 20% less pressure and load as compared to seamless pipe.
2 Length Relatively shorter in length due to manufacturing difficulties. Can be manufactured in long continuous lengths.
3 Size Manufactured for nominal size 24 inch or less. No such size restriction on production.
4 Corrosion Resistance Less prone to corrosion, means more corrosion resistant. Weld areas are more prone to corrosion attacks, means less corrosion resistance.
5 Surface Quality Rough due to extrusion process Smooth high quality surface as compared to seamless pipe.
6 Economy Costlier More economic
7 Production Process Complex, long procurement lead time Simpler, short procurement lead time.
8 Tests Seamless pipes does not require testing for weld integrity. Must be tested before use.
9 Application Suitable for high presure temperature and corrosive environment Normally used for less corrosive and low pressure environment.
10 Availability Less available, limited material types, longer delivery time Readily available for various different materials; shorter delivery time
11 Wall Thickness Inconsistent wall thickness across length, thicker so heavier Wall thickness more consistent than seamless ones, thinner
12 Ovality Better ovality, roundness Poor ovality and roundness as compared to seamless counterpart.
13 Internal surface check Checking not possible Internal surface can be checked before manufacturing
Pipe Selection, Welded or Seamless?

Even though improved manufacturing methods of recent time can produce welded pipes comparable to seamless pipes, still the seamless pipes are preferred in a maximum of the cases. However, for large size piping applications (>24 inch NPS) welded pipes are mostly preferred due to less cost. Along with cost various other parameters like diameter to thickness ratio, availability, corrosion resistance, etc. are considered for pipe selection.

How is a welded steel pipe made?

Most welded steel pipes are from steel plates and steel strips. These strips and plates are made by moving steel loops and coils with a proper thickness gauge to form a leveled material. The flat leveled material is then measured and cut to the desired lengths.

The process starts with bending the steel plate, and then it is welded to the desired shapes, be it a circle, rectangle, square, and many more using a progression of bending machines or rollers. The metallic pipe weld using a powerful energy source. Some pipes can also be welded together with filler material. Most welded steel pipes must pass through the heat treatment process.

The weakest piece of a welded steel pipe is always the joints. The weld joint’s quality determines the quality of a welded pipe—welding with a robot mostly in automated production lines such as in the automobile industry. Alternatively, for stronger steel pipe welds, human labor has proven to be perfect; for example, in aerospace construction.

Welded pipe starts out as a long, coiled ribbon of steel called a skelp. The skelp is cut to the desired length, resulting in a flat rectangular sheet. The width of that sheet’s shorter ends will become the pipe’s outside circumference, a value that can be used to calculate its eventual outside diameter.

The rectangular sheets are fed through a rolling machine that curls the longer sides up toward one another, forming a cylinder. In the ERW process, high-frequency electrical current is passed between the edges, causing them to melt and fuse together.

An advantage of ERW pipe is that no fusion metals are used and the weld seam cannot be seen or felt. That’s opposed to double submerged arc welding (DSAW), which leaves behind an obvious weld bead that must then be eliminated depending on the application.

Welded pipe manufacturing techniques have improved over the years. Perhaps the most important advancement has been the switch to high-frequency electric currents for welding. Prior to the 1970s, low-frequency current was used. Weld seams produced from low-frequency ERW were more prone to corrosion and seam failure.

Most welded pipe types require heat treatment after manufacture.

How is a Seamless Steel Pipe Made?

Seamless piping begins as a solid cylindrical hunk of steel called a billet. While still hot, billets are pierced through the center with a mandrel. The next step is rolling and stretching the hollow billet. The billet is precisely rolled and stretched until it meets the length, diameter and wall thickness as specified by the customer order.

Some seamless pipe types harden as they’re manufactured, so heat treatment after manufacturing is not required. Others do require heat treatment. Consult the specification of the seamless pipe type you’re considering to learn whether it will require heat treatment.

At this point, the seamless steel pipe forms through the following process:

A hot rolled seamless steel pipe manufacture is from forging billet, perforating, rolling, and shaping. The tubing is manufactured through an industrial extrusion process and is used to manufacture thick-walled seamless steel pipes and large diameter pipes.

On the other hand, cold drawn seamless steel pipes use the cold-drawn technology, which is suitable for pipes that are of small diameter and thin-walled since they have a lower material strength. It is also useful when the goal is to manufacture a stunning pipe with a smooth internal surface. During the extrusion process, the seamless steel pipes can only roll using a low alloy structure, carbon structural steel, or an alloy structure.

Some seamless steel pipes often harden during the manufacturing process; in such cases, the manufacturer will not use heat treatment methods.

Historical perspectives and use cases for welded vs. seamless steel pipe

ERW and seamless steel piping exist as alternatives today largely due to historical perceptions.

Generally, welded pipe was considered inherently weaker because it included a weld seam. Seamless pipe lacked this perceived structural flaw and was considered safer. While it’s true that welded pipe does include a seam that makes it theoretically weaker, manufacturing techniques and quality assurance regimens each have improved to the extent that welded pipe will perform as desired when its tolerances aren’t exceeded. While the apparent advantage is clear, a critique of seamless piping is that the rolling and stretching process produces an inconsistent wall thickness compared to the more precise thickness of steel sheets destined for welding.

The industry standards that govern the manufacture and specification of ERW and seamless steel pipe still reflect those perceptions. For example, seamless piping is required for many high-pressure, high-temperature applications in the oil & gas, power generation and pharmaceutical industries. Welded piping (which is generally cheaper to produce and is more widely available) is specified across all industries as long as the temperature, pressure and other service variables do not exceed parameters noted in the applicable standard.

In structural applications, there’s no difference in performance between ERW and seamless steel pipe. While the two can be specified interchangeably, it wouldn’t make sense to specify for seamless when cheaper welded pipe works equally well.

Cost of Seamless Steel vs. Welded Pipe

Strength and durability are some of the factors that determine the cost of both welded and seamless tubing. Seamless steel is stronger than welded pipes, making it more expensive because of the higher production cost.

On the other hand, welded steel pipes are easier to manufacture due to the cheaper cost of production and raw material availability. Also, the production process of seamless steel is complicated and time-consuming. Since each of the tubings has its unique features, advantages, and disadvantages, there is need to learn about acceptable purchasing practices to develop a reasonable budget.

Healthy Purchasing Practices for Seamless Steel and Welded Pipes

Good purchasing habits go a long way in cutting on material costs by minimizing any metal pipe waste. It also ensures that the best material completes the job.

Here are some tips to remember in your next order:

Understand your environment – The environment that the metal pipe will be exposed to should determine which metal tubing you will purchase. If it is in a less corrosive climate, you can go for welded steel, but if it is in a highly corrosive environment, spending lots of money on seamless steel will be worth it because it will last longer.
Plan ahead – Having an excellent work plan is key to saving you thousands of dollars. A simple technique will help you understand the exact quantity of metal pipes with all their intended dimensions. It, therefore, makes it easier to do procurement and place orders on time.

Contact an expert – Whether you are sure of what you want or not, always seek a professional opinion just to be sure. Someone who has been in this field for decades has the kind of experience you will need to budget and buy the right thing. Contact our offices to learn about welded pipes and seamless steel

Place your order on time – Placing orders earlier allows you to plan on your finances and enable you to purchase the right pipes. Placing an order is as simple as sending the pipe specs, getting your quotation, and within no time, you will receive your consignment.



Seamless pipe Specification, standard and identification

Seamless pipes are extensively applied for the nuclear device, gas, petrochemical, ship building and boiler industries. Seamless pipes dominates 65% of market share in Chinese boiler industry.