For a company that usually builds ship elevators, hydraulic machinery, steering gears and cargo handling systems for the US Navy and the marine industry, the idea of building a one-of-a-kind launch table for the new Delta IV rockets at Cape Canaveral was certainly new for Jered Industries, Inc. of Brunswick, Georgia. The massive 540 ton, three-story launch table structure would take 60,000 man-hours to complete. And, the project came with its own set of challenges, especially in the area of welding.
"This was one of the most challenging jobs we have ever completed due to the enormous size of the launch table and the aggressive delivery schedule" said Mark Holt, Manufacturing Manager at Jered Industries, Inc. "In addition, we also faced a number of technical issues because of tight tolerances for the massive structure, the requirement for full penetration welds and the potential for distortion. Overcoming these challenges required creative manufacturing and welding techniques."
The $11 million launch table's purpose is to support the rocket before and during the countdown. Internally, the structure protects cryogenic fuel pipes, electrical cables, electronics and monitoring equipment such as remote controlled cameras and ultraviolet sensors. Attached to the table are launch mating units which contain mechanisms for holding the rocket in place as the engines build up to launch thrust and takeoff. In addition, three, 150 ton flame deflectors guide the rocket exhaust safely away from the most sensitive areas of the structure to avoid permanent damage to the table and its contents.
The launch table will support and sustain the US Air Forces Evolved Expendable Launch Vehicle program. It is designed to launch many commercial weather and communications satellites as well as a host of military missions.
With dimensions of 76 feet in length, 40 feet wide and 23 feet high, the launch table was no small task for the 50 fabricators at 55-year-old Jered Industries, Inc.
After winning the business through a competitive bid process, Jered identified the welding and other fabrication challenges that were required of this job. These included:
The design of the launch table called for Jered Industries to maintain tight tolerances, for certain critical features. For example, the position of the Tail Service Mast Interface (TSM) flanges, and the Fixed Pad Erector Mounting Flanges had to be fabricated within 1/8". This was a significant challenge for a structure manufactured from 1 ½" plate with full penetration welds.
Since almost every weld on the job had to be full penetration and ultrasonically tested, Jered had some welding challenges for joining hard-to-reach peaks and corners; some with 30° angles.
The launch table assembly required that many stiffeners be joined to the 1 ½" thick plate and that subassemblies be welded together. All of this created a great potential for weld distortion and the need for carefully determined welding sequences during all aspects of the fabrication process.
Jered had to weld the launch table to a number of different codes including AWS D1.1, AISC, and GSE (Ground Support Equipment) which governs construction for anything that is used to help transport or launch rockets. Each code provided its own specifications and further complicated the job.
Jered's procedures and the customers specifications required close monitoring of the weld quality and dimensional integrity of the Launch Table. This demanded close coordination between Jered's manufacturing and quality personnel and the customer's quality team.
"One of the first things we did was put together the fabrication plan which included meeting with the design engineers, planning subassemblies and deciding which welding processes to use," stated Dick Klaar, Welding Engineer at Jered Industries, Inc.
For panel welds, prior to sub-assembly, Jered representatives determined that the best efficiencies for welding the 1 ½" thick plate together with full penetration butt welds could be achieved by using a Submerged-arc welding (SAW) process. With SAW, deposition rates are high, and the arc is completely covered by flux, which means that the weld can be run quickly without the flash, spatter and sparks that characterize open-arc processes. In addition, the nature of the flux is such that very little smoke or visible fumes are developed.
"We determined that the Submerged arc process was up to 75 percent faster than flux-cored arc welding for this project," claimed Klaar. "But we still wanted to go even further to make our Submerged arc welding the most efficient it could be."
To do this, Jered called on the expertise of The Lincoln Electric Company and representative Brian Hart. With his input, Jered invested in two Lincoln DC-1500 power sources because of their higher output capabilities and potential for higher deposition rates. Jered wanted to use the L-50™ wire and 880 flux combination because of its operator appeal and because it provided for easy slag removal. At Jered's request the company performed certification tests and provided a certificate of conformance for the wire/flux combination.
So just how was welding accomplished to not only achieve efficiencies, and overcome some of the challenges mentioned earlier?
To perform its Submerged arc welding, Jered Industries welded one side of the ASTM A-36 and A-572 grades, 1 ½" plate and then used a crane to flip the piece over to weld the other side - no back-up was used for this process. A total of five submerged arc welders were set-up at the plant for this purpose, each one utilizing a Lincoln LT-7 wire feeder.
"With the Submerged arc process we could weld with minimal gouging or grinding," said Klaar. "It was easy to use, and didn't require much operator training. We were getting high quality welds without the spatter and smoke that is characteristic of other processes. The rejection rate for our Submerged arc welding was less than 1.5 percent."
Klaar also commented on the new power sources and wire employed for this project. "Our operators were impressed with the DC-1500 machines and the potential for using larger diameter wire (such as 3/16) for greater deposition rates."
To fabricate the table, Jered Industries first joined plates together as described above using the Submerged arc process. Flux-cored processes, for the all-position welds, were then used to join the remainder of the project which included using an egg crating technique to join stiffeners, adding the stiffeners to the plate with fillet welds, and then erecting the subassemblies together.
To minimize the distortion discussed earlier, Jered Industries used proper welding sequences from the center out with a backstepping technique. In addition, the company pre-heated every piece of metal to reduce the amount of residual stresses in the weld and adjacent base metal. Usually, the metal will cool off quickly and pull in toward the center, but by preheating, Jered was able to slow the cooling rate so as not to put too much strain on the weld.
Creating full penetration welds at the launch table's intricate peaks and corners meant having to carefully cut the plate to get the proper welding angle. Jered also used a 60° double bevel from both sides so that the amount of filler metal put into joints was decreased.
Flux-cored welding for the stiffeners and subassemblies was accomplished by using Lincoln DC-600 power sources in combination with LN-9 boom-mounted wire feeders and LN-25 portable units. Stick welding was limited to where inaccessibility of a gun necessitated it.
Klaar credits Lincoln with working hand-in-hand to help develop some of the welding procedures for the project and also for training the operators on how to operate the new submerged arc equipment. "With Lincoln, I had help in the planning," stated Klaar. "The company's representatives are knowledgeable and can answer questions
To move the launch table when it was completed, a number of trailers (with more than 282 wheels) were needed and a special roadway built from Jered's building to the waterfront. A barge carried the launch table to its final resting spot in Florida.
You can bet that when the employees of Jered Industries hear the countdown to launch the Delta IV, it won't be the rocket they are looking at like everyone else…it will be the launch table!
Originally Written 6/19/01