By Tony Piwowarczyk, Director of Business Development, Field System Machining
Some things in life are predictable. Every spring, the swallows return to San Juan Capistrano. Every spring, Chicago Cubs fans start out with high hopes, only to be disappointed. And each spring, maintenance crews return to power plants during scheduled shutdowns.
With annual shutdowns, every minute detail can be listed out such as: personnel, equipment, parts, materials and schedules. Unplanned outages, though, are another matter. These can crop up under circumstances such as a cracked blade root tip causing rubbing or a circulation pump failure requiring emergency attention to bring the equipment back in production immediately.
Since every day the unit is off line or producing below capacity means lost income and potential penalties, there usually isn’t time to send parts into the shop for welding or machining. Instead it is essential to bring in a field machining company for rapid repair. These firms typically have trucks and crews on standby to reach a plant within hours, but speed of arrival doesn’t necessarily equal the speed of repair. Here are five tips for getting repairs completed in the minimum amount of time while guarding against future downtime.
Fixtures First: Except for simple equipment such as a flange facing machine, there is no one-size-fits-all approach to portable machining. The equipment needs to have the proper fixtures to hold and manipulate the parts being machined. Those fixtures must be engineered and machined in a traditional machine shop before loading onto the truck for the field repair.
Thus, it is important to understand that the first portable machining company to arrive may not be the first to complete the project. Some, for instance, load a truck with boring bars, milling machines, portable machine shops and men and race to the site as quickly as 10 minutes after receiving a purchase order. But once they arrive, they have to spend time reviewing drawings and the machine, spend some hours meeting with staff and then formulating a repair procedure.
What comes after that? Fixturing. Where does that fixturing occur? On site, at a local machine shop or more likely, at the shop they just left to race to the job. Understand before calling, then, that it’s the first to complete that is the single most important factor.
Provide Complete Data: To minimize downtime and ensure a quality repair, it is essential to provide the field machining company with accurate information, ideally before they leave their shop. This includes drawings, photographs and a written work scope. Without that information, the field machining company will have to do a site inspection to prepare for the repair. This unnecessarily adds to outages.
To eliminate the need for the initial inspection, the maintenance manager, purchasing agent, outage planner or project engineer should supply (in electronic format if possible):
- Dimensional drawings showingwhat exists currently and what it needs to be after repair. If you don’t have a dimensional drawing, make a dimensional hand sketch or CAD drawing.
- Written work scope documenting existing as-found and desired as-left conditions.A written work scope ensures that the machinery is machined to the condition you want it. Take the time to write a work scope—nothing fancy, nothing long—bullet points are all that are needed.
- Distances and clearances to all obstructions near the machined area.
- Composition of material to be machined or welded.
- Bolt circle, size, thread, depth, pattern, if the field machining equipment is being bolted to a bolt circle or bolt pattern.
- The material of the frame if the fixture is to be welded to the frame. Field machining equipment usually needs to be mounted to the machine being repaired or to the floor.
- Photographs of the equipment taken when the machine is torn down for inspection and in operating condition.Photographs (with a stretched tape measure visible) should show not only the dimensions of the work piece area(s) but also show obstructions (walls, pipes, columns, beams) and clearances around the area to be machined.
- Date the outage starts, date the outage ends, how many of the outage shifts are dedicated to the repair and how many shifts of the outage the repair area will be accessible.
Prep the Site: To shorten downtime, preparation pays dividends. Don’t wait until after the machinists arrive to have the mechanics tear down the machinery. Otherwise, expect to receive a work change order increasing both the price and the length of the repair if the machining company incurs standing time. The work scope order should also spell out if millwrights are needed for tear down and reassembly. Finally, don’t expect reassembly after welding/machining, if the machining company on site didn’t disassemble it.
Know Lead Times: Lead times can vary widely. Emergency stud removal mobilization time, from the time the field machining company receives a phone call until they are driving down the road could be as little as fifteen minutes. At the other end of the spectrum, though, machining down a 15-5PH, 12-inch-diameter shaft journal area, fitting a new 155PH stainless steel split sleeve, welding that sleeve in place, and machining it back to 12.0005 inches could require a one-month lead time due to having the sleeves custom forged and heat treated prior to machining to size, all of which occurs prior to arriving on site.
Know Your Material and Its Condition: Is the material being machined 410SS, 309SS, carbon steel, cast steel, cast iron or some other alloy? Has the material been heat treated, torched, hardened, exposed to constant high temperatures or otherwise had its properties changed? Has it been welded? How was it welded?
Recently, a hired a field machining company to machine six areas on a trunnion ring. The wear areas were stick welded prior to the field machining company’s arrival. Two of the six areas were mistakenly welded with a non-ferrous weld media resulting in massive glass slagging and excessively hard conditions. These two areas, due to the errant weld procedure, required multiple 12-hour shifts of hand grinding prior to resuming machining.
The plant thought they would save money using their welders instead of the machining company’s welders. The end result was a 40 percent increase to the estimated price, due to work scope increase.
Your Place or Mine: When looking at direct costs, field machining is more expensive than shop machining. But those direct costs are only a portion of the total costs of a repair. In many cases, the primary cost is downtime, not the repair itself. When time is not a major factor—for example if the repair is done during a month-long planned outage or in the case of a peaking turbine being worked on during the off season—removing the component and sending it to the shop for welding or machining may be the best option. Field machining, on the other hand, is the lowest cost alternative when it absolutely, positively cannot come apart and/or when the repairs absolutely, positively have to be done in the shortest amount of down time.
Budgeting a Field Repair Job
There are five main line item costs to any field machining project.
- 1) Shop prep. This cost includes all material for fixtures, labor hours for fixture design, labor hours for fixture manufacture and labor hours to prep and adjust machines.
- 2) Mob/demob of men and machines. For emergency jobs, a “hot shot” or dedicated truck driving straight through to the destination delivers the fixtures and equipment. If it is 500 miles or less from the field machining company’s shop to your plant, the field machining company will typically use its own trucks and men for mob/debmob. For emergency jobs where distances greater than 500 miles, a driving team of two professional drivers and dedicated truck are often used. In the latter instance, the machinists and welders are typically flown in. In extremely expensive per-hour-down forced outage situations often found in power plant settings, all tools, fixtures, men and machines can be flown to the job site.
- 3) Machine and tool rentals. A field machining project may require anywhere between $20,000 and $250,000 worth of field machining equipment. The field machining company typically owns all of its machines and charges a nominal daily rate. Occasionally, highly specialized but rarely used machines are necessary and the field machining company rents those machines from machine manufacturing companies specializing in renting specialized, expensive portable field machine tools.
- 4) On Site Labor. This cost runs any ware from a low of 30 percent of the cost of a job on up to 80 percent or more of the cost of a job—depending on the length of the job and the distance traveled.
- 5) Lodging/Per Diem/Rental Cars. Typically around 8 percent to 13 percent of the cost of the job is the expenses incurred by the men while on site. Several things can lead to an increase in the price estimate, including but not limited to crane/off loading delays of equipment, standing time waiting for access to the equipment, time spent on site attending mandatory safety training, incorrect specifications, incorrect dimensions, obstructions not disclosed on the drawings, or incorrect material composition being reported.
For example, inaccurately reporting in your work scope that the material is a 50 Rockwell hardness which turns out to be a 70 Rockwell hardness is going to dramatically increase both the outage duration and total price. Also, if the quote is issued as “weekday pricing,” but when the time comes the repair occurs over a Saturday and Sunday, expect a reasonable increase for the higher overtime rates.
Using Time and Material pricing, rather than fixed pricing, allows the field machining company to invoice only exactly the costs spent repairing the machinery. When asked to bid “hard money” or “not to exceed” the company is forced to consider “what if scenarios” and factor that into the hard money bid.
Quoting is half art and half science because field machining entails, literally and figuratively, many moving parts. An agreement that the budget is a good faith estimate which could go up or down, could save you money in the end.–TP
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