There are many methods of making carbon steel pipe, but the two basic methods result in seamless pipe or welded pipe. There are several different processes for joining the pipe seams together, such as Electric Resistance Weld (ERW), Electric Fusion Weld (EFW) or furnace butt-weld. Though it should be noted that the most common processes are ERW and EFW.
- Standard pipe (seamless and welded) is used for air, gas, steam, and water lines for threading or welding and suitable for flanging or bending fall. Carbon Steel Pipe is ordered under the specification ASTM A53.
- Standard pipe (seamless only) is used for high temperatures and is suitable for flanging or bending. Carbon Steel Pipe is ordered under the specification ASTM A106.
- Line service pipe (seamless and welded) is used for transporting gas, oil, petroleum, and water. Carbon Steel Pipe is ordered under the specification API Spec 5L.
Carbon Steel pipe can be triple stamped so that it meets the criteria of ASTM A53, ASTM A106, or API 5L. Each of these specifications requires that the pipe be marked with the spec that it is manufactured to. The pipe will also specify the grade (e.g. Grade A, Grade B), which determines the specific metallurgy of the carbon steel pipe.
Even though both of the processes below can vary, the result is the same - "pipe."
Seamless pipe is extruded into a solid steel tube (billet). The billet is heated to the proper temperature to be pierced. It is then cut to a length and pulled as it advances over the piercing tool, which forms a continuous hole. This process happens again to reach the proper size desired. Before going further, the pierced billet is reheated.
In the next operation, the pierced billet is rolled over a plug that reduces the diameter and wall thickness and increases the length of the billet. Small sizes go to the next step. For large sizes, the previous process is repeated. The next step is the same for all sizes - the pipe is advanced over a mandrel, where both the inside and outside of the pipe are brushed and cleaned.
Reheating is needed again to obtain an even temperature. It is passed through a series of rollers to give it the exact size and roundness, then placed on a conveyor belt where it begins to cool and straighten. The final steps are facing and beveling, followed by inspection. If it is rejected during inspection, it may become structural grade pipe or line service pipe. If it passes inspection then goes to loading and shipping.
Welded pipe comes in coils from storage to the mill. The coil is flattened and electrically welded together to form a continuous sheet. Once the proper circumference has been reached, the process of forming the sheet to a round and continuous edge begins. Next the high frequency welder heats the edge then pressure squeezes the heated edges together to form the weld. The weld is inspected for any defects that may have occurred.
After the seam has been worked, it is cooled to the temperature required before sizing the pipe. Once the pipe has passed through rollers that give the proper outside diameter and strength it is cut to a specific length. Next, it is hydrostatic tested and put through straightening rollers. The final step is facing and beveling. If it passes inspection then it goes to loading and shipping. If it is rejected during inspection, it may then become structural grade pipe or line service pipe.
At the time of manufacturing, mills will reject pipe that cannot be graded as a prime product because of physical or chemical imperfections. Pipe that passes inspection is sold to distributors and manufacturers. The pipe that did not make the cut is sold with no warranty - you buy as is. Rejected pipe, also known as structural grade pipe or line service pipe, can still be used in some cases if manufactured to ASTM or API standards. The rejected pipe comes in all types, sizes, and materials and can still be used for purposes other than prime pipe: fencing, casing, posts, supports, etc.