Brewing Up Copper

Brewing up copper: one brewery, two projects, no rework


The copper steam coils of a brewery’s mash cooker periodically need to be replaced. This type of project presents some unique challenges. Space inside the cooker unit is limited, welding copper requires significant amperage, and finally, like all repair work in an operating facility, the outage time must be as short as possible – little if any time is allotted for rework.

The traditional method for replacing steam coils in a mash cooker is to weld them in place using manual gas tungsten arc welding (GTAW) and copper backing rings. However, two recent projects showed that the traditional process isn’t the only process for replacing steam coils.

Project One

In the fall of 2001 the R.L. Bunch Company, Torrance, Calif., was contracted to perform the welding portion of a coil replacement project. The copper pipe, pipe preparation, and even the backing rings were supplied by another contractor. Conventional processes and equipment were to be used for the entire project.

BREWING UP COPPER
Figure 1: Replacing the copper steam coils in a brewery’s mash cooker unit is a complex project that requires precision bending, end prep, handling, and welding of various tube sizes.

Project Parameters. Each mash cooker has 12-foot, 10-ft.-, and 8-ft.-diameter steam coils. The steam coils are made of 8-inch or 6-inch diameter, 1/4 in. wall, SB-42/GR-122 copper pipe (see Figure 1). The pipe is bent to the proper radius and the ends are hand-ground to a standard 37-1/2 degree, 1/16-in. land preparation. The final coil configuration is installed at the bottom of the mash cooker tank that measures 14-1/2 ft. by 20 ft. All personnel and equipment enter and exit the tank through a single 24-in.-dia. Access way on the top of the cooker tank (see introductory photo).

All the work was to be performed in an operating brewery with a minimum outage time and no disruption to the other mash units’ operations or overall brewery activity.

Decision to Automate. The R.L. Bunch Company has used automated orbital welding systems for many of its welding projects. Because the company already was familiar with automated welding equipment and the project time frame was to be minimal, the contractor and the brewery agreed to use mechanized orbital pipe welding, instead of manual welding, for as many of the welds as possible.

Selection Criteria. Selecting the right orbital pipe welder for this job was critical. The weld head would have to handle the high-temperature preheats (up to 600 degrees F) and would have to be mounted and rotated on a curved pipe with a 4- to 6-ft. radius. The short distance between some of the coils and the tank walls posed clearance and access challenges.

R.L. Bunch chose an Arc Machines, Inc. (AMI) Model 15 weld head and an AMI Model 415 power supply to perform the welds.

The weld head was chosen because it met the preheat and mounting restrictions. The head has an axial length of 10.5 in. and can accommodate a radial clearance as small as 3.875 in. With the proper guide ring, it can weld any size pipe down to 2 in. It also can be used to weld flat plate and handles standard V joints, U grooves, J preps, compound preps, fillet welds, and seam welds. In addition, the guide rings for this model are the only commercially available rings that mount on curved pipe without special tooling, which eliminates an additional cost.

The power supply was chosen because of the high current required to weld copper pipe. It delivers up to 400 amps at 00 percent duty cycle.

Results. Not having to manually access the back sides of the coils, a cumbersome procedure in which a mirror is needed to view the process, reduced the welding time. The use of automated welding resulted in a twofold increase in productivity compared to manual welding. Furthermore, using automated equipment was safer than trying to get into position for manual welding with a 600-degree preheat.

copper
Figure 2: Some of the tubes were prepped and capped at the fabricator’s shop before being transported to the brewery. The rest of the work was performed on-site.

Interim

The first project did have several challenges, most of which involved backing rings. They were difficult to fit to angular pipe and were known to cause some maintenance problems during tank operation. In addition, because the pipe and rings were already cut, prepped, and supplied for the project, everything had to be fitted in place inside the tank. Welding within the confines of the tank presented another set of challenges, including the need for scaffolding and ventilation and limited weld access.

After the project was completed, but before any subsequent projects were put out for bids, Steven Bunch, vice president of R.L. Bunch, sought a better way of prepping and fitting the pipe. He consulted with AMI and R&B Welding Applications, Chatsworth, Calif., to discuss ways to eliminate the backing rings. They decided to switch to a J bevel preparation with a butt-to-butt fit-up.

R&B worked with Bunch to get the right prepping equipment and to assist in developing a welding procedure. Weld samples performed according to American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Section 9 met quality and repeatability criteria.

One trade-off was that the J preparation requires an ID purge, whereas the use of backing rings eliminates ID purge. However, the J bevel approach cut the weld time by 50 percent.

The samples and test results were shown to the customer, and even though this type of weld had never been attempted on the coils before, the customer approved the procedure and asked all bidders to perform the welds in a similar manner.

Project Two

In the fall of 2002 the R.L. Bunch Company was again contracted to perform the coil replacement on two mash cooker units. For this project, R.L. Bunch supplied the pipe, prepped it, and welded it.

Of the 24 automated welds per tank to be performed, eight were made at R.L. Bunch’s fabrication shop. The remaining 16 welds had to be done inside the tank after the pieces were taken through the access way. This notwithstanding, all joints were prepped at the fab shop and prefitted before being taken to the site and installed in the cooker.

Because of the pipe’s curve it was determined that the best choice to cut and prep was a model 200 split-frame, OD-mounted, portable pipe lathe for elbows made by Machine Technologies Inc., Marseilles, Ill. A cutting template was made to ensure the angular pipe would fit up square and allow the prepping equipment, which also was supplied by Machine Technologies, to mount properly and cut the J prep on the pipe. After prepping and a fit-up check at the fabrication shop, each pipe end was cleaned and capped and not touched again until it was inside the tank (see Figure 2).

Because the pipe was prefitted at the fabrication shop, on-site placement and fit-up went much smoother and faster than in the first project. The 24-hour workday that was required for the first replacement was reduced to one shift of 12 hours.

According to Bunch, “The planning, J prep, and reliability of the equipment resulted in a twofold increase in productivity on-site and in the prefab work at the shop.” The J prep also reduced the preheat time required to bring the joint up to temperature. The welds in the second project also were performed without rejects or rework, the time frame allotted for the outage was achieved, and the tanks successfully returned to operation.


Reprinted from the Fabricator
August, 2003