Confined spaces are one of the most common challenges boilermakers face during tube installation and maintenance. From squeezing into drums to working in tight utility rooms, space constraints are present in all aspects of the job. In order to get a job done quickly and effectively, it’s important operators have the proper tooling on hand. Using the wrong tooling can make the job harder and pose safety concerns.
Watertube Boiler Drums
Watertube boilers are a vertical design consisting of a steam drum at the top of the bundle and a mud drum(s) at the base. There are several types of vessel designs, each with its own set of space limitations.
During tube installation or maintenance, operators are often required to lay down and hold tooling over their heads. This can pose both ergonomic and safety challenges for the operator. The most common motor used in boiler tube installation is a right-angle rolling motor. While these high-torque motors are designed to roll tubes in confined spaces, they can be heavy and bulky. Working inside drums, operators are often in a position that makes it difficult to brace or react to torque, increasing the risk of injury.
One of the best ways to reduce fatigue and improve safety is to use a motor suited for the job. In smaller, package-style boilers, tubes are generally smaller and have thinner tube sheets and drums, meaning less torque is required to get the job done. In these applications, a smaller motor with approximately two-thirds the torque can give the operator more freedom of motion and eliminate injury caused by overpowered, 90-RPM motors. Additionally, in applications where operators are rolling to feel instead of to a specific torque, a stall torque motor can be a great way to reduce weight and size.
In cases where more torque is required, having the ability to react to torque can reduce some of the strain on the operator. If space allows, a torque reaction bar is highly recommended for operator safety. In tight spaces, operators will often place a smaller tube inside of an adjacent tube, allowing the tube sheet to absorb excess torque, reducing the force on the operator. Additionally, some prefer to use a roll or twist throttle motor when working in drums in the case an operator gets stuck and cannot release the lever throttle.
Benefits of Short Mandrels
While most tubes in watertube boilers are straight, there are curves where the tubes connect into the drum. The location and bend radius of the curve is important, as it can limit the expander and mandrel that can be used in that application. In some cases, a standard drum mandrel will be too long to be used within the tight bend. As a result, many operators will modify their existing mandrel by removing some of the length to get them to fit. However, this practice is not recommended, as it’s easy to remove too much material and change the expansion range or function of the tool. Instead, a series of short mandrels should be used to accommodate the tube bend and achieve the necessary expansion. Depending on the tube size, short mandrels kits can consist of two to four different mandrels with varying diameters and tapers. When used in sequence, these mandrels will achieve the proper wall reduction.
In situations where someone cannot fit inside the drum and rolling is required, operators will work through a hand hole. Hand holes are generally used to conduct visual inspections or maintenance and are sealed when the vessel is in operation. In these situations, it can be difficult to see, so U-joints, parallel gear drives, and right-angle drives can be used to help position the tool inside of the drum.
Compared to watertube boilers, the configuration of a firetube boiler makes it a lot easier for operators to access the tubes and tube sheets. Typically horizontal in design, firetube boilers consist of straight tubes rolled into tubesheets at either end of the vessel and a furnace.
In field maintenance, boilers are often located in small or confined rooms with limited access to the vessel. In some instances, the operator can’t get direct access to the tube sheet, making it difficult to position tools and rolling motors. A reverse mandrel is highly recommended to allow the operator to roll tubes from the opposite end of the vessel. This can be done using a series of extensions to connect the motor to the tool and complete the rolling operation from the opposite side.
Combustion Return Areas and Wetback Boilers
The design of the wetback boiler can be frustrating due to the limited access to tubes in the combustion return area. Like rolling tubes in a watertube drum, the combustion area is very small and requires someone to crawl inside to perform any tube work. One way to avoid working directly inside the combustion area is to use a reverse mandrel and expand the tubes from the opposite end of the boiler. This process uses an extension and a socket to connect to the expander’s reverse mandrel. The type of mandrel used will vary depending upon the style of the expander. Reverse-type mandrels can be used for flaring and straight rolling tube expanders, whereas forward square mandrels can be used with combination roller beading expanders.
Another method is for boilermakers of smaller statures to roll from within the combustion return area. This process requires a right-angle pneumatic motor with a series of short mandrels that can work in the limited space.
Overall, working in confined spaces can be a challenge for operators in both watertube and firetube boilers. In order to get the job done quickly and effectively, it’s important that operators have the proper tooling on hand. Using these tips and tricks can help make a difficult job easier and improve operator safety.