Marnie Surfaceblow: Don't Pick Up Bad Vibrations

Long-time POWER readers may remember Marmaduke Surfaceblow, a fictional character whose engineering escapades were brilliantly portrayed in hundreds of stories published within POWER magazine’s pages over more than 30 years beginning in 1948. Today, the fictional series continues through Marmy’s granddaughter, Marnie, who is an engineering wiz in her own right.

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Cutting maintenance costs can make you penny-wise and pound-foolish, unless you evolve your maintenance practices with the times.

A lone car traveled an empty road through a bleak snow-scattered field. The driver was a young Indian woman, barely looking old enough to rent a car but sitting with a quiet and stoic bearing implying much greater age. The passenger was a woman in her mid-50s of Scots ancestry, who despite her smile wrinkles and a touch of white mixed in her brown hair carried the bearing of a much younger age.

The younger woman tried to maintain her composure while shivering intensely—the rental car’s heater had died soon after departing the Oulu, Finland, airport. The older one, however, was staying warm by playing Crimson Day’s “Raising the Fury” on the radio and accompanying the music with feverish head-banging and drumming the dashboard with a pair of knitting needles.

Born and raised in Maharashtra, India, lead field engineer Maya Sharma had never encountered weather below freezing until she was hired by her passenger. Marnie Surfaceblow, vice president of Surfaceblow & Associates International, hated the cold like William Wallace hated the English, but unlike Wallace, she was prepared for her enemy.

“I told you Maya—you need heated socks, heated gloves, heated everything. I’ve got 200 watts degrading to heat, I’m drumming to this awesome beat, keeping warm from my head to my feet, and this coffee is so hot and sweet!” On cue, Marnie paused for a swig from her thermos.

“Ye-es, ma-am, next t-t-time I will take your advice and b-b-become Mistress Electricity. I n-note your n-newest p-personality quirk is lyricism.” Maya’s contralto voice expressed exasperation toward the cold and the loud music.

“It won’t be much warmer at the plant—they’ve been in an outage since they detected that combustion turbine vibration. I guess you could say it’s shivering too,” Marnie said with a little giggle. “Oh, I know you said you didn’t need them, that you weren’t afraid of the cold and all—but I packed a pair of heated socks and gloves for you in the bag behind your seat.”

Maya’s smile couldn’t be suppressed—“Best boss in the world!”

Delivery Delays Allow Discretionary Work

Sited on a hill overlooking the frigid dark blue Gulf of Bothnia, the Vellamo power station at first seemed abandoned—even the guard shack was empty. As they parked their car next to the engineering building, Marnie and Maya were warmly greeted by a surprisingly small Finnish engineering crew. Plant manager Tarja Parviainen, a small wizened woman, introduced her key staff members—lead engineer Marko Kakko, maintenance leader Alexi Virkkunen, and operations superintendent Kaarina Korhonen. They were ushered not into the expected conference room, but directly into the spacious but vacant control room. Both Marnie and Maya welcomed its tropical temperature and a variety of hot drinks to complete their personal defrosting process.

After an exchange of business cards and pleasantries, during which most of the site staff wandered in, Tarja began the customary briefing meeting. “Our existence is providing baseload power supporting an offshore wind farm. We generate 380 MW from the combustion turbine and 190 MW from the steam turbine, with flawless operation for three years. Last month, we come down from switchgear failure. Spares are at the corporate depot, but storms closed the road and two weeks until the parts arrive. Being practical people, we performed routine maintenance during the outage.”

“Very wise,” Marnie noted. “What activities did you perform during the outage?”

Tarja thought for a moment, then responded, “There was a leaking seal on the steam turbine that was making the floor a mess. We changed lube oil for the steam and combustion turbine. We did some air filter changeouts, repaired a baffle at the heat recovery steam generator outlet, and did compressor washing.”

Alexi chimed in, “My team washed the compressor blades and cleaned the inlet duct for the combustion turbine. We tuned a faulty combustor can and replaced a bad thermocouple on the turbine exit duct too.”

Maya raised a hand. “Ma’am, it appears few personnel are employed here. I would expect 30 for a combined cycle plant such as yours, but I noticed as we passed the locker room there are only 13 lockers with names. Does that cause problems with operations and maintenance?”

Tarja smiled and nodded toward Marnie. “Clever, your assistant. Would I had twice the staff. Headquarters says, ‘You have new combined cycle, it runs by itself!’ But somehow always we are busy, and they say our four managers and 13 staff are sufficient. During any major outage, headquarters sends a floating crew augmenting our workforce.”

Startup Marred by Vibration Issues

Marnie nodded again. “What happened when you started the unit up?”

Kaarina answered, “I lead the startup sequence, and we bring the combustion turbine up through its first and second critical speeds quickly. The peak second critical speed is 72% of operating speed, then it reaches normal vibration at 90% operating speed. But when we start, instead of decreased vibration after 72% speed, the vibration increases. Finally, at 94% operating speed we trip on relative motion to the bearing housing.”

“What about seismic vibration of the bearing housing relative to the foundation?” asked Maya.

“That was not so bad, but it was greater than ordinary. We tried re-starting and the result was the same. Then, we tried letting the combustion turbine sit between critical speeds one and two for it to warm up greater, and then move quickly through critical speed two—as that is a thermal transient vibration. But matters were unchanged. Marko investigated some items for us?” Kaarina said, looking at her compatriot.

Marko, a young man with a scraggly look, scratched at his beard before responding. “I examined the vibration monitors, and they appear to work to specifications. I replaced one probe with transient problems, but the problem did not change. I examined the lubricating oil and saw nothing unusual,” he said.

“You will notice from the vibration readouts …” Tarja passed printouts around, while Maya looked at them on her tablet, “the vibration appears to be strongest on the compressor side, although it is difficult to determine.”

“And the vibration during the first critical speed is almost normal,” Marnie said after looking over Maya’s shoulder. “It’s the second, thermal transient that never seems to end. What are the trends of compressor inlet and outlet temperatures compared to historical operation?”

Marko nodded. “Good that you should ask. The average compressor outlet temperature is normal, but there is much variation in value. See—compressor outlet temperature normally varies 10 to 15 degrees Celsius in normal operation at full load. But here we are static at 50% full load and the temperature varies 25 to 30 degrees C. At 90% speed, temperature variation is becoming widely variant, up to 40 degrees C from the mean.”

“When you increase or decrease loading or speed, does the vibration change?” Maya asked while frowning at the data, trying to determine what went afoul. Before the plant staff could answer, Marnie injected, “Has anyone looked at the compressor to see if you had a catastrophic failure, say a piece of compressor blade breaking off and doing 3,000 bank-shots per minute off the compressor housing?”

Two questions warranted two replies, with Kaarina answering first, “We could not change load much as we were not synchronized. Speed is the principal variable in the vibration.” Then, Alexi chimed in, “Me and two staff opened inspection ports and finally took the shell off. There was no visible damage. In fact, the blades looked the same as when we finished washing them.”

A distant memory of something that seemed familiar troubled Marnie. She cleared her head and raised her coffee cup, asking Tarja, “Do you have anything stronger than this?”

Tarja gave Marnie a cold look, replying through gritted teeth, “You of all people must know we have a strict alcohol ban on all our corporate sites, especially power facilities.”

Marnie made a sardonic face. “Saint Drogo preserve me … I mean stronger coffee. Let’s go to your break room and I’ll concentrate on concentrating the coffee, while I think about what could be happening. Maya, continue please.”

Unusual Thrust Readings

As Marnie departed, Maya asked further questions, and received answers. The compressor was typically washed every year, and the outage occurred such that it had been nine months since its last cleaning. No cracks were detected in the turbine foundations. The firing from each of the combustor cans was balanced to well within the original equipment manufacturer’s specifications. The air filters that were replaced were the same as had always been used. Lastly, no inlet air cooling nor heating system was used at the plant.

After an hour of questions, Maya graciously thanked the plant staff for sharing information, and as everyone had chores to work on, she was soon left in the control room with the youngest plant operator, Eino Heikkinen. Maya examined trend after trend of data, and then sighed, closed her eyes and pinched the bridge of her nose. She dozed for a few minutes, waking up as Eino gently set a cup of hot tea in front of her.

Thanking the operator for the drink, Maya started reviewing the data when Eino asked, “Excuse me miss, but could it just be bad bearings along the shaft?”

“A bad bearing is always a possibility, but it is reported the bearing wear is within tolerances.” Maya paused, then asked, “Why do you ask?”

Eino scratched the back of his neck. “Well, I noticed whenever the vibration is worst, the thrust bearings see a lot of force on them. It’s fast and small vibration—way below our alarm point—but look at these trends, miss. The plant has never indicated so much axial movement,” he said.

Maya looked at the data plots from the last three startup attempts. The thrust bearings always showed high deflection as turbine speed increased, but the magnitude was still variable.

Marnie’s voice could be heard as she returned to the control room with Tarja, carrying a coffee mug the size of a large oil can, “… and that is how you squeeze the last few molecules of caffeine from the bean. Maya, my protégé, how goes the hunt?”

“Mr. Heikkinen pointed out curious data regarding the thrust bearing, which I think may be another clue,” Maya said, passing her tablet to Marnie.

Marnie reviewed the notes and the thrust bearing data, and pursed her lips. “Ah. Hm. I think my nagging suspicion has become a reality. Anyhow, make sure your new electric togs are charging, and fill yourself up with something warm. Tarja says they’re going to try another startup in half an hour, and the windchill is –50C.”

The look of horror in Maya’s eyes could not be faked. “It may be best for me to remain here and continue data analysis,” she said.

Marnie paused, then placed a reassuring hand on Maya’s shoulder. “Thank you for taking care of yourself. On a job site everyone needs to be aware of when environmental conditions are beyond the pale, and speak up. Don’t worry my friend, I hate the cold like Garfield hates Mondays, but my fiery Scots blood always gets me through it. I’ll go inspect the turbine during startup, and record what I find.”

Maya looked at Tarja, who mouthed along with her, “Who’s Garfield?”

A Really ‘Cold’ Start

The wind was steadily blasting from the sea as Marnie tried to keep warm. Pacing next to the combustion turbine intake housing, she took out her new extendable audio probe and practiced some sabre fencing drills with it to warm up (Figure 1). Marko and Alexi gave the crazy Scots engineer plenty of room, and finally Alexi had to ask, “So, I fenced at university, but do not know that style. What is it called?”

1. In an effort to stay warm, Marnie practiced her fencing technique while standing by to test the combustion turbine. Source: POWER

“Bronze triangle,” Marnie replied while catching her breath. “It’s never used because it cuts and protects low to the ground, just as you would if you were really on horseback. It catches many opponents off guard, as they get so into the routine of fighting only on foot, forgetting other possibilities.”

Further conversation was cut short by a klaxon, warning startup was impending. Mechanical clangs and whines signaled startup had begun, and the turbine came to life. Touching the intake structure with gloved hand, Marnie felt the turbine pass through the first critical resonance point, then as the speed increased, she donned wireless headphones and placed her audio probe against the compressor inlet housing.

Minutes passed. The structure shuddered briefly as the turbine passed through the second critical point. Hearing something that she should not be hearing, Marnie closed her eyes and focused, then opened them and moved to another location, then another, testing each with her audio probe. A different klaxon announced the turbine was shutting down, Marnie nodded toward the engineering building, and the three returned to warmth.

It took two cups of coffee and almost 30 minutes for Marnie’s hypothermia shivers to dampen to where she could talk. “Open t-t-t-urbine inlet d-d-d-uctwork. B-b-b-ring space heaters,” she said.

“No, let us not waste time,” a clearly irritated Alexi said. “My team cleaned everything possible in there. There will be no dirt, you will see.”

Tarja overruled the maintenance leader. “We can open the side hatch. It will not take long. Do it quickly before it grows colder,” she said.

The inspection hatch lay propped against the compressor intake housing. Marnie, having carefully watched a video on site-specific training for confined space entry procedures, shone her high-powered green laser through the hole to check for obvious obstructions, tested the air with her combustible gas and CO monitors, then deftly crawled inside. Maya, Tarja, Alexi, and Marko shone their own lights through the hatch, looking for anything amiss. A wild ululation of joy, amplified by the metal structure, made them jump. Suddenly, Marnie was at the hatch and holding something wrapped in a large shop towel.

After fully exiting the intake structure, Marnie removed her full-face dust mask and smiled broadly. “Back to the control room, so I can show you the gremlin I caught,” she exclaimed.

Leftovers

Plant staff gathered and waited good-humoredly as Marnie went through another defrost cycle. Maya helped bring her boss back to functioning by rubbing her hands for her. “I am sorry I did not assist, ma’am,” she said, almost hanging her head.

“Don’t be. I’d rather have a safe and healthy protégé than one who is shipped back in a coffin. I mean, do you know what a nightmare Customs would be like? ‘Anything to declare?’ ‘Oh, just a dead Indian woman, and some chocolates.’ ” Maya couldn’t help but snort with laughter.

Once enough ice had retreated from her skin, Marnie stood and addressed the group. “I’ll be brief. There are several phenomena that can lead to combustion turbine compressor vibrations—poor combustion control, manufacturing or installation defects, damage to the rotor and compressor blades, bad bearings, poor foundations, and problems with the air intake system including the silencer, the coarse and fine particulate filters, and the air pre-heating or chilling systems. In this case, however, the culprit was forgetfulness.”

2. Marnie presents her findings from the combustion turbine compressor intake inspection. Source: POWER

Unwrapping her shop towel, Marnie produced a frayed and flattened roll of brown plant paper towels (Figure 2). Silence reigned, and a couple of expletives were voiced.

“Yes, folks, another way you can unbalance a combustion turbine compressor is inlet air flow disturbance. Modern combustion turbines gulp down enormous amounts of air, and thus you need clean airflow to prevent vibration or oscillation. And if you are, oh, washing the compressor and intake structure, and you’re in a hurry due to a staff shortage, then it’s possible for someone to leave something potentially destructive behind. I found this caught against the final grating leading into the compressor, and the airflow disturbance it caused led to the cycling oscillation that shook the entire turbine.”

Tarja, staring at the paper towels with mute horror, finally asked, “How did you know?”

“By a high-tech version of the mechanics’ stethoscope.” Marnie flourished her audio probe like a magician and her wand. “When I touched the side of the intake structure, I started hearing a low moaning sound that became a banshee’s wail by the time you hit 90% load. Either it really was a banshee, in which case you were out of luck, as I left my exorcism kit at home, or something was left behind after the compressor cleaning,” she said.

All eyes turned to Alexi, whose face burned with anger. “OK! Maybe one of my team was rushed and left it behind. It is your fault, Tarja, for not giving me enough staff to maintain the plant!”

Maya raised a hand. “Forgiveness please, but no, sir. It is also your fault as maintenance leader to inspect the work of your subordinates. If you cannot complete the task with your resources at hand, then respectfully, do not take on the task.”

Alexi swore and stomped out of the control room. Tarja shook her head, and said, “He is a good maintenance leader, and a good man. I will speak to him, and we will use this as, how you say, a learning moment?”

Kaarina and Marko examined the paper towel roll. “Is it possible the compressor was damaged?” asked Kaarina. Marko quickly inquired, “Is there any way to prevent this in the future?”

Maya replied first. “I would recommend you engage experts in non-destructive testing of the compressor. No overt damage has been witnessed, but stress fractures could have formed and may cause problems in the future.”

Marnie nodded. “I remember a similar incident, except the turbine was loaded up to full power, and the vibrations broke several pieces of blade, destroying the compressor. Now that was a dreadful way to begin the month.”

Maya continued, “You must also be certain all work areas are inspected and signed-off as such, and consider taking detailed photographs or video each outage before sealing equipment, so others may view them and see something left behind.”

The meeting concluded and everyone at the plant lined up to shake Marnie and Maya’s hands, with several taking selfies with them. Tarja hugged each of them quickly, then said, “It’s too late and too cold for you to be heading back. Come stay at my family’s house tonight. Our children are gone, so me and the husband have spare rooms, and I think sautéed reindeer, fresh bread, cheese, and lingonberry porridge are on the menu.”

Blanching at the prospect of eating reindeer, Maya said, “Thank you, ma’am, but I do not wish to make Santa Claus angry by eating reindeer.”

Laughing, Marnie turned to Maya, saying, “Well, shoot, what do you think Santa Claus eats? I assure you it isn’t his elves. At least, not since they unionized!”

—Una Nowling, PE is an adjunct professor of mechanical engineering at the University of Missouri-Kansas City.