You can make big productivity gains when fabricating boilers and pressure vessels, and by implication many other large engineering products, by looking at the process you use. In this article Nitin describes how his company made significant productivity advances by moving from a traditional way of fabricating vessels and heat exchangers by moving to the production line concept – made famous by Ford and then Toyota.
The Production Line Concept
A production line, also called an assembly line or factory line, refers to the organized path of assembly for a product. In most cases, the production line centres on a conveyor belt or other mechanical system that physically moves the product from one station to the next. It is a common misnomer to call this conveyor a production line. At each station in the production process, a factory worker or machine adds a piece to the finished product, performs a quality control check, or some other job that is essential to the completion of the project.
The word production line or station concept refers to a manufacturing unit which continuously manufactures a same kind of product. Our company manufactures heavy pressure vessels and reactors, and we have thought of implementing the same. Initially, whenever an order was given to the company, it was given to the specific manufacturing shop where, except the activity of rolling the shell segments, all activities are done: long seams, circular seams, shell-section manufacturing, internals-externals manufacturing and welding, and hydro testing. In this set up, we perform all activities one by one, and the skill set is limited. When the task time is minimised, it opens the possibility of multi-tasking.
Implementation of the station concept
After implementation of station concept, different areas are defined for different activities. There are stations for:
- shell rolling – all shell plates are rolled here in required diameter
- shell manufacturing- the rolled shell segments are joined together to make a shell on this station. Specialised fixtures are made to expedite the shell segment set/up process
- shell circular seams set/up (shell # shell joint) – after making the shells from shell segments, the shells are joined by doing circular seam set up on this station
- shell circular seams welding – the joined shells are welded on specific SAW (Sub-merged Arc Welding) station
- overlay welding – the shells in which the stainless steel or inconel overlay is required are sent to this station for overlay
- nozzles and internals – externals manufacturing and welding on job. After joining shells or making segments by joining, shells are sent to this station for set up and welding of nozzles, internals & externals
- hydro testing – when the equipment is ready after doing required NDT and heat treatment, it is released for hydro testing which is done on specific hydro testing bed made on that station
A simple production line for the same is as mentioned in line diagram.
As the line diagram indicates, there are different stations for different activities. There are no problem with resources as the particular station will be well equipped with everything needed for that station. Before, each manufacturing shop had to maintain and keep all resources starting from welding machines, overlay welding machines, turning rollers and even resources for hydro testing. After implementing the station concept, the resources can be kept in good condition in one particular area. There is no shortage of machines or any other resources. Likewise, a day’s production line or station concept is more useful and even beneficial not only in manufacturing small products, but even in the big projects, and thus, improving the quality and productivity.
Equipment delivery improved by 30%
In the before scenario, when all the activities except shell rolling were done in the same manufacturing floor, the resource arrangement and station arrangement was a task that needed specific manpower and time. This was more tedious because of resource engagement in other shops and transferring them to the required place. Instead of this, we implemented the station or production line concept where the resources are allocated to the specific station.
Looking at the man power part, the technician’s skill set has drastically improved in a particular activity as they keep on doing the same activity on particular station which gives better quality and productivity. That becomes completely beneficial for the company. However, they lose their touch on other skills, while skills of supervisors or engineers working on each particular station get enhanced.
The drawback of the production line in big equipment manufacturing is transportation cost of shells. However it is not that huge in comparison to the benefits of production line concept, as 90% of the transportation is done by wagons running on rails spread over in between the stations.
In beginning we faced problems like machine break down, and because of that, a specific job gets delayed. To address this, dedicated maintenance technicians were allotted to each station (2 technicians per station). This ensures the technicians’ skills set is up to par for the particular station, and the machines are also maintained in good condition. There are no big problems faced, even now. It’s now easier to trace the job progress status. By implementing the station concept, the equipment delivery has improved by up to 30%. However, it is still in its starting phase, and there is still room for improvement in each station.