Originally installed in the late 1950s, a national electric power generation plant’s pulverized coal-fired boiler system was in need of a retrofit. The task at hand was the replacement of the steel piping system used to convey pulverized coal from the pulverizers to the burners. Eight of the 16 discharge pipes were taking a beating and needed to be replaced as a result of the extremely abrasive nature of the pulverized coal pneumatically conveyed through the system.
Although the current retrofit only called for replacement of half the piping, this was the third replacement project in the boiler’s 50+ years of operation. A complete replacement of the piping system occurred in the 1970s, and again in 1998. During the last retrofit, the system was upgraded to one of the toughest abrasion resistant pipes on the market.
The plant’s experience with its piping system is anything but unique. Instead, it speaks directly to the extremely abrasive nature of the fine, pulverized coal and its devastating effect on the inner wall of the pipe as it
For a highly abrasive application such as pulverized coal, mild steel pipe was not tough enough to stand up to the abuse for more than a year or two.
“Mild steel is inexpensive, but it’s not going to hold up over time,” said Greg Fynan, the engineer that handled the retrofit in 1998 and again for the current project in 2011. “It isn’t less expensive in the long run because the labor costs to change a piping system are astronomical.”
Fynan estimated it would take two weeks, two shifts a day, with 15-20 workers per shift during scheduled downtime to replace the piping.
Fortunately, a number of “abrasion resistant” options are on the market. Based on the principle that the harder the inner wall, the better it resists the gouging or plowing action of abrasive particles, available abrasion resistant pipe is often rated on the Brinell scale of hardness (BHN). Whereas standard steel pipe rates a relatively “soft” 120 BHN, A-R (abrasion resistant) steel pipe measures 200 BHN. Options of more than 600 BHN include cast iron or basalt-lined pipe.
As the engineer assigned to the project, Fynan, who has more than 30 years of experience in the power industry, also oversaw the replacement of the entire piping system in 1998. Complicating matters at the time, most of the existing pipe segments were constructed with some kind of bend, even multiple bends, in a relatively small area. This precluded the possibility of rotating the pipe to compensate for wear, a common practice.
As a result, he was looking for an abrasion resistant pipe that could be bent to match the existing layout. Ultimately, he made the decision to utilize a unique abrasion resistant pipe from Ultra Tech, in Port Washington, Wis.
“When we looked at it in 1998, the Ultra Tech product was not only extremely abrasion resistant, but it could be delivered with bends that matched the original piping systems,” Fynan said. “There aren’t many companies bending 12” abrasion resistant pipe.”
For its Ultra 600 brand pipe, Ultra Tech begins with a steel pipe manufactured to a proprietary chemistry, followed by induction heating, and finally water-quenching the inner surface to create the required hardness of the pipe ID. At a very hard 600 BHN, the inner surface of this pipe is extremely abrasion resistant, and tapers to a 250 BHN outer surface that is ductile enough to be cut and welded and can accept a variety of end options (flanges, weld rings, couplings, etc.).
Tensile strength is increased as well with this secondary processing of the steel. Induction hardened pipe can last up to 3-8x longer than mild steel, with only a moderate price increase.