by John Parker
As he made his way into the turbine hall, he was conscious that this might be his last visit, at least in connection with this dying project. After opening the test vessel, he removed the specimens and wrapped each separately for the journey back to the lab. The test had been running for 3,000 hours, which was about one tenth of the time the failed LP disc had been operating, before the incident.
He had plenty of time for a run. This was a wonderful area to run across, mainly heathland with few restrictions to the public. After a shower and a sandwich, he drove back to the lab and delivered his specimens to the non-destructive testing engineers, for them to make their first inspection. He stressed the importance of avoiding contamination of the surfaces of the test pieces. They confirmed that this would be no problem with the pre-cracked specimens which they would x-ray, but they could not effectively check the plain specimens loaded in the test frame. The best that they could promise, as far as an in-situ test was concerned, was the careful use of dye-penetrant solution on a couple of the specimens on the outer edge of the group. Although this would contaminate the tested surfaces, they could protect the other specimens. Dave settled for this as he could discard these two specimens if he decided to return the others for further exposure at Winford.
*
Sue received a surprising phone call. She had just made a start on her new book, Mrs Dalloway. The man’s voice clearly betrayed a Midlands background. Having confirmed that it was Sue Harrison, formerly Turner, with whom he was speaking, he explained that he was her cousin Eric, Auntie Clara’s son. He went on to say that his mother had passed on to him some family papers before her death and, having heard from their Uncle Stan, about her research into their family’s history, he was interested in learning how she was progressing. He lived in Fordingbridge, which wasn’t far and he wondered if they could meet. He realised that it was short notice but he would be passing through Chippenham the following day, on his way to visit an old RAF pal, and wondered if she might be free for an hour, late morning. Although a little wary, Sue welcomed any opportunity of talking to anyone who had an interest in, better still might be in a position to make a contribution to, her research. She agreed and suggested the local pub.
The Marden Arms was quiet when Sue arrived, having enjoyed the walk through the Highwood Estate. She would have no trouble spotting Eric. She had a recollection of seeing him at a family wedding when she was about ten and he would have been in his early twenties. When Eric arrived Sue waved rather unnecessarily, considering there was only Sam and his local wag in the bar. He joined her and placed a carrier bag on the floor by the table, before collecting drinks.
After a trip down memory lane, Eric steered Sue into her well-practised spiel. Eric expressed surprise with the progress she had made. He was able to add some colour to her recent findings with a few anecdotes. She was amused, as he related a variety of incidents relating to the Turner side of the family. Being about ten years older, he could recall some events unknown to Sue. On several occasions she had cause to laugh out loud as Eric dug deeper into his store of gossip. She found him a joy.
“Anyway, enough of these preliminaries.” Eric reached down into his carrier bag and brought out a tattered bible. “Thought you might like this. As I’m on my own now, it’s likely to be of more use to you than to me.” Sue was delighted though embarrassed and suggested that she would be happy just to borrow it. Eric insisted. He was content for it to have a good home. He handed it to Sue, who carefully opened it.
“Oh my goodness! How absolutely wonderful,” she cried, when she saw that inside the front cover was a list of hand written notes with names and dates of various family occasions. At the top there was the name ‘Caroline Potten, Brighton 1863’ in copperplate. This was the great grandmother whom she was attempting to identify from the two candidates. At Eric’s prompting, Sue found more entries on the back sheets.
“I can’t believe it,” laughed Sue, her enthusiasm drawing attention from Sam behind the bar. Eric explained that his mother, Sue’s Auntie Clara, had been keen to keep family business private. He would have contacted her earlier had he realised its significance. He allowed Sue to buy him another half of bitter before leaving.
*
“We’ve been trying to contact you,” said the voice on the phone. “George here, Non Destructive Testing. We’ve been having a look at your specimens and you may be surprised to know that we’ve detected significant cracking. Thought you’d want to know straight away.”
Dave said that he’d be over shortly. He didn’t think that it was surprising that crack growth had occurred in the pre-cracked specimens. After all, he had noted the suggestion of crack growth during his earlier inspection at Winford. The tests had been running for some weeks since then and the use of x-ray techniques was much more sensitive. This result would not be a surprise to the other sub-committee members, as Joe had already reported crack growth in his laboratory steam rig. It would, however, be interesting to compare the rates of growth between the two tests.
George, after lighting his pipe, took Dave through the results. All the pre-cracked specimens showed an increase in crack length, in other words the pre-existing crack had penetrated more deeply during exposure to the Winford turbine steam. “Well, that’s great. Thanks George. Everyone should now be convinced that a defect in a disc could extend in normal service in an LP turbine without any contamination present and so, all similar turbines are at a slight risk. It may be just good luck or good pre-assembly inspection, that has prevented other failures. I suppose it might be argued that only defects that are sharp and ‘crack like’ in shape could cause this growth and the presence of these is unlikely. I’ll go and knock out a brief report for the sub-committee.”
“Aren’t you interested in the others, that are loaded into that test frame?” asked George, indicating the assembly on the opposite bench with the stem of his pipe. Dave confirmed that he was, if only for the record. He was wondering whether it might be worth putting those back in the test vessel for further exposure. He might as well use the Winford rig until the end of the year when the job finally closed. “I thought that you’d like to know that they’re already cracked, at least the two that we checked are,” said George. Dave was shocked, he couldn’t believe it. Surely there was some mistake? Of course, the confined space within the test frame would make it difficult to examine the specimens in any detail, so it was probably a misinterpretation. George assured him that, although it had been tricky, they had been able to do the job. There was no doubt that the samples checked were cracked and well cracked at that.
Dave was shaking as he carried the test frame back to his own lab. Gritty caught Dave’s mood as soon as he heard the news. He took the frame to the do-it-yourself workshop and cautiously slackened off the load from the two specimens tested and carefully removed them. Dave examined the length of both of the specimens under a high-powered bench microscope. Some discolouration in the black surface film was evident. What did Gritty think? He was not sure.
“Bugger it, let’s sacrifice one of them,” declared Dave decisively.
They assembled one of the specimens into a tensile testing machine, which was normally used for stretching specimens to failure to assess tensile strength and other mechanical properties. They gently applied an increasing load, which gradually stretched the Winford test piece. As they began and before any appreciable load had been applied, they were amazed to see small cracks opening up along the surface. Normal steel test pieces, loaded in this way, would gradually distort and not show surface cracking until very near their failure load.
“Bloody hell, it’s cracked to buggery, I can’t believe it.” Gritty and Dave almost danced around the lab. They decided to continue loading this specimen to failure, upon which it was clear to see, on the otherwise bright fracture surfaces, a crescent shaped area of discolouration. This was the area of the stress corrosion crack and was almost identical to the appearance of the fracture surface on the failed Winford disc.
The procedure was repeated on the second specimen with a similar result. Following this, Dave asked Gritty to carefully remove one of the other specimens, which had not been exposed to the NDT dye-penetrant fluid. He was delighted to find this also cracked. The other specimens were left undisturbed so that they could be used for demonstration purposes for anyone doubting their claims.
Dave was shaking as he took in the serious implications of this discovery. He was delighted, as he believed that he had produced the most unexpected result in the field of stress corrosion for years. Stress corrosion cracking in high purity steam! No one would believe it, but he had the proof. He had his specimens and he had Bunsen’s steam analysis. The steam quality had remained high throughout. He didn’t know what to do. He called Mike Pearson and Bunsen, both of whom had been so helpful to him. Ian had already arrived having been attracted by the noise of the two of them.
A couple of hours later Dave was still in a daze of pleasure. He was brought back to earth quite suddenly, as he realised that his personal joy at the findings would not be shared by the Authority or other utilities operating turbines of the Winford type. These results would send shock waves through many organisations. All turbines of this type were at risk of sudden catastrophic failure. Many had been in operation for much longer than Number 2 turbine at Winford. It was only the fact that the Winford discs had been unusually brittle that caused failure with such small cracks present. Other LP turbine discs still in service would, almost certainly, contain cracks and possibly some deep ones. There had already been one fatality resulting from the Winford failure. Next time, things could be much worse. Though there were usually few people around turbines under normal operation, more were present when measurements were being taken, or during turbine run ups, shut downs and overspeed testing.
Time was getting on and Dave was anxious to make a start on writing his report. He had the odd irrational fear that if he didn’t claim the credit for this unexpected discovery, someone else would beat him to it – probably tomorrow. There was no point phoning Sue to tell her the news and say that he might be late home, as he knew that, as it was Friday, she would be at her blessed Peter’s group indexing.
He settled to his work. Ian helped initially by taking a selection of photographs of the specimens and their cracks. They had photographs of the specimens before testing and the Station Chemist at Winford had taken a nice shot of the test rig in operation. Gritty cut a couple of sections through one of the specimens and prepared them for examination under an optical microscope. These showed other cracks, typical of stress corrosion, which he photographed. Soon Dave had all the illustrations that he needed and his colleagues went off on their weekend.
He stayed on and wrote his draft report, outlining the object of the experiment, and the on-site equipment details, together with the specimen design and purpose. He added the steam analysis record, quoting maximum and minimum values for impurities, which were miniscule. Then, finally, the results and a brief discussion, with such great pleasure, followed by his conclusions and recommendations. It was just past midnight. He spent the weekend putting the final polish to his report, which he would get typed first thing on Monday.
18
Sue was delighted with the Potten family bible which, via the Loomes family, came down to the Turners. It was heirlooms such as this that family historians loved to possess – a tangible link with their past. It had been her great grandmother Caroline’s, whichever one of the two candidates she turned out to be. Caroline would have been seventeen years old when she wrote her name inside the cover in 1863. Amongst other things, she had listed the name of her husband and their children. The bible had been passed down to Sue’s grandmother, Caroline Jane, who had carried on the tradition, recording her marriage and children’s birth, including Sue’s father. This was wonderful. She could now add more detail on her Turner ‘family tree’.
Sue was overcome by her great grandmother’s foresight and she determined, despite her difficulty with the Potten line, that this was one ancestor whom she felt an obligation to pursue, and she would. That being accepted, Sue decided that she should narrow down her research, for the present, to two families – the Boughtons and the Pottens – as these appeared to be the most fruitful.
Her thoughts turned to the forthcoming summer holidays. She knew that Barry and Velma were planning to go to Hunstanton. She wondered if they would mind having Jo and Katy along for part of their stay. There was no doubt that the cousins would welcome their company. This would give her and Dave the chance to spend time together. Impulsively she phoned Velma and found that she was happy to help out, positively enthusiastic about the whole idea. Velma and Sue’s sister had intuited, from their weekly phone calls, that relations between Sue and Dave were shaky at present. So Velma’s enthusiasm was, in part, a kindness to her sister-in-law as much as a favour for the girls.
Dave’s euphoric mood lasted for days and he gladly endorsed Sue’s suggestion. He thought that he could take a few days off work, following the forthcoming sub-committee meeting. This would allow time for all his colleagues to digest his fantastic results, especially those smoothies at the Slough labs, he thought with relish.
“These are great results David.”
Tony had already scanned Dave’s report on the on-site rig experiments. He was pleased as this would be a feather in the Department’s cap. He would discuss it with Sweety. They considered the wider implications of the results. Tony was thinking of how best to present them to the general scientific community.
“Is this the first time that stress corrosion cracking of steel has been observed in high-purity water or steam?”
Dave replied that from his own knowledge, plus an extensive literature search, it was the first time in the case of medium strength, mild or low alloy steels. Tony, after pausing for a moment, demonstrated to Dave one of the qualities of a good section head.
“If your results are correct, how do you explain the pattern of cracking found in other turbine discs on the failed rotor? I understood from the conference, the Slough people were arguing that the most severe cracking occurred in the inlet region of the LP turbine, where there was the greatest concentration of steam impurities and it was this contamination which caused the cracking.” Dave was taken aback, not by the question itself but rather that Tony had been astute enough to ask it. Clearly he had been keeping up with all the developments and understood the detail of the investigation. Dave replied that the observed pattern of cracking could still be explained if no contamination had been present, by virtue of the temperature variation along the LP rotor. The main requirement was that moisture was present, which it was, albeit cycling between wet and dry, near the inlet. The operating temperature of the various discs depended upon their position on the rotor, the hottest being near the steam inlet. This was where the worst cracking would be predicted. As the steam cooled the extent of cracking would be less severe, with little or no cracking near the steam exit. So the pattern of cracking was as expected, even without steam contamination. Tony thought about what Dave had said and after a moment, he suggested that Dave should begin preparing a scientific paper as, he believed, it would take some time to get into print. He should contact the editor of, say, Corrosion Review to obtain their instructions to authors.
“This is just the kind of thing that the Strategic Supplies Authority needs to fend off their critics. Let’s get our own trumpet blown as soon as possible. Well done David.”
Dave reverted to the train for the next sub-committee meeting. He had been unable to arrange another overnight stay. His work had begun to build up again and he had agreed with Sue to take at least a week’s break, whilst the girls were away.
In addition to producing a draft paper, he had begun laboratory tests in an attempt to resolve the most difficult problem of all – just how cracks could initiate in high purity steam. He envisaged that a crack-like surface defect was a necessary precursor to the process. Resolving this was an essential part of his hy
pothesis. He hoped that Pauline would understand.
On his arrival at the meeting room, Joe congratulated Dave upon his draft report, which he had received the previous day. He was pleased to see that their separate results of crack growth rates, were in good agreement. Dave was full of pride as the others arrived. Henry thanked him for the report and was as charming as usual. Dorinda and James avoided the subject and their conversation centred on the positive feedback they had received from the conference. True to form, Henry had kind words for them too. They took their places around the table. Pauline arrived on cue. She smiled pleasantly around the group without any obvious distinction to any member. Dave marvelled at her. He still could not believe it. Pauline was back to her civil service best. If only the others knew. He immediately dismissed this thought as Henry opened the meeting.
James expanded upon the comments that the Central Research Labs had received following their conference. Amongst them were several from noted authorities on the subject of stress corrosion, who agreed with the conclusion that sodium hydroxide contamination was the cause of the cracking and that mechanical carryover of this from the boiler water during commissioning, probably at times of high boiler water levels, was responsible.