July 8, 2017
How did the need for spirally welded pipes come up in the Oil & Gas welded pipe segment.
The Line pipe industry in India in the 90's predominantly in the Oil and Gas segment were either using ERW pipes or the longitudinal pipes for its requirement for transmission of oil and Gas. While water pipes were fabricated at site in shells of 2 to 3 meter in length and then circumferentially welded to form a double random length.
ERW pipes had manufacturing limitations in manufacturing large diameter as beyond 24 inches and had rolling limitation on the wall thickness beyond 14.5 mm. Therefore pipeline projects of large diameter necessarily opted for Longitudinal as an option.
However Longitudinal pipe ( DSAW) of large diameter like 56 inches needed plates of a width 4470 mm where manufacturers of steel who could deliver the same were limited to European or Japanese steel mills which made the product very expensive . API though allows double longitudinal seam 36 inches and above oil and Gas companies were reluctant to use the said mode and did the same only in dire necessities to complete the project unwillingly as they preferred single longitudinal seam.
Spiral welded pipes thus evolved to circumvent the said problem of meeting requirements of large diameter pipes though initially they were only used in Water segment they gained confidence of usage once they were used and implemented in USA for Oil and Gas projects.
In the year 2003 a study was commissioned by Gail (India) Ltd on the technology used by various international oil and gas majors for high pressure large diameter gas transmission pipeline systems, where operations are very critical. In September, a committee of senior Gail executives visited major gas pipeline operators in Europe including British Gas, Transco, Bechtel, Exxon Mobil, Gas de France, British Petro-leum, and Total Fina Elf to discuss the type of line pipes being used for gas transportation.
As Gail is in the process of implementing various high capacity and large diameter pipeline projects in the country, it had also commissioned Engineers India Ltd and Tractebel of Belgium to study various types of line pipes manufactured using the LSAW (Longitudinal Submerged Arc Welded), HSAW (Helically Submerged Arc Welded) pipes, also known as spirally welded pipes and the electric resistance welded (ERW) technology. Both EIL and Tractebel recommended usage of LSAW pipes for high gas transmission large diameter pipeline systems.
Large diameter pipes above 16 inches are manufactured either by LSAW or HSAW method and line pipes in sizes smaller than 16 inches are manufactured by ERW process. HSAW process of manufacturing utilises hot-rolled coils as the starting material for formation of pipes. Pipes are formed by spirally deforming the HR coil. Continuous welding of seam by submerged arc welding is done after forming. Sizing operations using cold expansion is not carried out due to the presence of well seams all over the pipe body.
While, the LSAW process of manufacturing utilises plates as the starting material. Plates are formed into cylinders/cans by UOE or JCO or three roll bending process. Formed shapes are welded from inside/outside by submerged arc welding process. These welded pipes are then expanded to get proper size and relieve stress.
Since the first pipeline was commissioned in 1986, Gail has been procuring LSAW pipes through international competitive bidding route while periodically reconfirming its superiority over HSAW pipes under Indian conditions.
Discussions of the Gails team with the global oil and gas majors revealed that most of these companies are largely using LSAW pipes for high pressure gas transmission systems. This is what they had to say :
British Gas: In general terms, HSAW is cheaper than LSAW as it is manufactured from strip steel. However, a considerably increased level of quality control is required to produce HSAW pipe. Because of this, engineers consider using HSAW as a lower cost but higher risk option. It depends on how much risk you are prepared to take and how much confidence you have in the manufacturing, construction processes. IN BG, we would use LSAW rather than HSAW, for offshore pipelines. Even onshore, we would usually consider using HSAW for liquids or gas pipelines of short duration in less-critical locations.
Transco UK: We have historically used LSAW because HSAW was not readily available in large diameters. The rest of Europe does not use HSAW in smaller diameters. Coils being comparatively more cheaper than plates encouraged the spirally welded pipes to be used in major projects.
With technological advancements and adherence to stringent specification being made possible by Spiral welded pipe manufacturers and capacity additions globally in the segment resulted in spirally welded pipes being accepted in the Oil and Gas Industry for all onshore applications.