Bad Steel in the Rolls-Royce Merlin?

pbehn · Sep 18, 2017

swampyankee said:
My point is that changes in processing can make a material (not just steel) suitable or not. .

Very true SY, this is a process that has been going on since metals were first melted. In my last years at work people discussed the effects of dissolved nitrogen in steel, in my early years there was no way of testing for it in a steel plant.

An engine goes through various phases of development. Sometimes huge power outputs are quoted for an engine on a test bed. However these are engines run for a short time and assembled under perfect conditions using specially selected and machined parts. To get this engine to a mass produced engine that will hold together in service for hundreds of hours is what takes the time and explains why the maximum produced on a bench is much more than that produced in service. Engineers design around what they have, they may request manufacturers to improve some aspect of what they supply but that is research for the future. In practice, from my experience the manufacturers write the specification which is approved by major clients. This is how a company called Kayser Ellison produce a material standard for high performance exhaust valve steel used only by companies like Rolls Royce.

MycroftHolmes · Oct 1, 2017

R A Gould's work suggested the opposite: that the steel used in RR Merlins was of better quality than that in Packard-made engines. He noted that when crashed aircraft powered by RR engines were excavated the engines were in much better shape than similarly-recovered Packards, due to impurities in the steel used in the American-built engines. I imagine though that aircraft in WWII had such short lives that this made little practical difference.

Shortround6 · Oct 1, 2017

A strange way to judge steel. What was important at the time was strength and resistance to fatigue. Which might very well call for a different alloy than resistance to corrosion. Steel parts that corroded in service were probably not getting enough oil.

pbehn · Oct 1, 2017

Shortround6 said:
A strange way to judge steel. What was important at the time was strength and resistance to fatigue. Which might very well call for a different alloy than resistance to corrosion. Steel parts that corroded in service were probably not getting enough oil.

It is no reason at all to make a judgement. Pure normalised iron corrodes quite slowly. In a welded pipe the weld will corrode more quickly than the pipe despite being much cleaner as regards impurities. The weld is a coarse grained structure. However the place that corrodes most is the toe of the weld because the weld and parent metal are different and set up a small galvanic cell.

swampyankee · Oct 1, 2017

When I took my metals class in college, the textbook mentioned that if one took a rubber band, wrapped it around a stainless steel tube, dropped it into tap water, and waited a couple of weeks, the rubber band would cut through the steel.

pbehn · Oct 1, 2017

swampyankee said:
When I took my metals class in college, the textbook mentioned that if one took a rubber band, wrapped it around a stainless steel tube, dropped it into tap water, and waited a couple of weeks, the rubber band would cut through the steel.

I dont know if that is true or not swampyankee, what is true is that there are a huge number of different types of steel especially stainless steels many of which will rust. All sorts of things can happen, I have seen a hole burrowed into a 2 inch thick carbon steel flange in three months purely by turbulence in the oil and galvanic action.

swampyankee · Oct 1, 2017

pbehn said:
I dont know if that is true or not swampyankee, what is true is that there are a huge number of different types of steel especially stainless steels many of which will rust. All sorts of things can happen, I have seen a hole burrowed into a 2 inch thick carbon steel flange in three months purely by turbulence in the oil and galvanic action.

Even if the book mentioned the variety of CRES, I got rid of the book years ago and couldn't tell you the alloy to save my life.The book did say to try it.

pbehn · Oct 1, 2017

swampyankee said:
Even if the book mentioned the variety of CRES, I got rid of the book years ago and couldn't tell you the alloy to save my life.The book did say to try it.

I wasn't doubting it SY I just havnt heard that specific example. Having worked in a stainless steel pipe factory for years, the most dangerous things to most stainless steels are plain carbon steel and salt water. The most expensive pipes I ever inspected were SS625 on the inside, X65 carbon steel as the "pipe" (for engineering strength) and a Monel coating. The splash zone on an oil rig is one of the most corrosive environments found anywhere and stainless steel just isn't good enough. Monel is an alloy of Nickel and Copper but that isn't a cure all for corrosion, a guy once built a boat with a Monel hull and it fell apart in six weeks, galvanic action ate the rest of the boat.

SKR_01 · Oct 3, 2017

pbehn said:
The original post was from a guy in Russia, the Merlin may have a different reputation there, but that may be due to operating conditions or different fuels and lubricants.

in general, I read about the use of Merlin in the Hurricane in the USSR and most of the claiming boiled down to a carburetor that was not suitable for frosts at -25 ° C

pbehn · Oct 3, 2017

SKR_01 said:
in general, I read about the use of Merlin in the Hurricane in the USSR and most of the claiming boiled down to a carburetor that was not suitable for frosts at -25 ° C

That is colder than any temperature I have experienced in UK.

SKR_01 · Oct 3, 2017

pbehn said:
That is colder than any temperature I have experienced in UK.

In the winter of 1942 near Stalingrad it was even colder) The water left in the carburettors froze and made the carburetors crack. By the way, I also learned that in the USSR the hurricane was reworked for flights on ordinary water, rather than ethylene glycol

pbehn · Oct 3, 2017

SKR_01 said:
In the winter of 1942 near Stalingrad it was even colder) The water left in the carburettors froze and made the carburetors crack. By the way, I also learned that in the USSR the hurricane was reworked for flights on ordinary water, rather than ethylene glycol

I worked in Russia (Vyksa) for a while, it is much colder than UK. However water entrapment isn't issue of bad steel. I believe the RAF used a water/glycol mix later in the war on safety grounds.

SKR_01 · Oct 4, 2017

pbehn said:
I worked in Russia (Vyksa) for a while, it is much colder than UK. However water entrapment isn't issue of bad steel. I believe the RAF used a water/glycol mix later in the war on safety grounds.

I know how cold in Russia. In my opinion, winter in Russia is the most pleasant and interesting time of the year.
Water in the carburetor is a common phenomenon and all have suffered as a disease as engines, including the USSR.

pbehn · Oct 4, 2017

SKR_01 said:
I know how cold in Russia. In my opinion, winter in Russia is the most pleasant and interesting time of the year.
Water in the carburetor is a common phenomenon and all have suffered as a disease as engines, including the USSR.

There is no reason that a solution couldn't be found apart from the huge distance between the front in USSR and Rolls Royce in UK. I cant remember Winston and Uncle Joe discussing carburettors much.

A Russian winter is much more pleasant than one in UK, snow at -20C is snow, at 0C it is cold water and the wind blows it everywhere.

Bollock brain · Oct 4, 2017

pbehn said:
Very true SY, this is a process that has been going on since metals were first melted. In my last years at work people discussed the effects of dissolved nitrogen in steel, in my early years there was no way of testing for it in a steel plant.

An engine goes through various phases of development. Sometimes huge power outputs are quoted for an engine on a test bed. However these are engines run for a short time and assembled under perfect conditions using specially selected and machined parts. To get this engine to a mass produced engine that will hold together in service for hundreds of hours is what takes the time and explains why the maximum produced on a bench is much more than that produced in service. Engineers design around what they have, they may request manufacturers to improve some aspect of what they supply but that is research for the future. In practice, from my experience the manufacturers write the specification which is approved by major clients. This is how a company called Kayser Ellison produce a material standard for high performance exhaust valve steel used only by companies like Rolls Royce.

Great stuff. So nerdy but fantastic , I am learning lots of things and have a whole new aspect of WW11 to annoy my wife with, which is wonderful theraphy.

pbehn · Oct 4, 2017

Bollock brain said:
Great stuff. So nerdy but fantastic , I am learning lots of things and have a whole new aspect of WW11 to annoy my wife with, which is wonderful theraphy.

Not really nerdy, it is engineering and the same applies in the modern world. The "floor plan" of a Volkswagon car costs much more to design and develop than a Rolls Royce car. However when completed it is the base of a range for all VW Audi Skoda and Seat vehicles whose production runs to millions. I don't know how much an exhaust valve weighs, but I doubt that all the Merlin exhaust valves ever made weigh more than a few tons, this is why military equipment costs a fortune.

I worked most to API 5L specification for pipes, which is American and written in English however the revisions for clad pipe API 5LD have some Germanic phraseology because it has lifted some technical statements from a German company. Even the American Petroleum institute cannot specify something that a manufacturer cannot make.

bobbysocks · Oct 4, 2017

SKR_01 said:
In the winter of 1942 near Stalingrad it was even colder) The water left in the carburettors froze and made the carburetors crack. By the way, I also learned that in the USSR the hurricane was reworked for flights on ordinary water, rather than ethylene glycol

i would like to see some reports or documentation about that. if a carb ices up in flight it doesn't crack and they can ice up to nearly closed. i don't understand why it would that if the ac was sitting....unless there was water in the fuel...which came from contaminated fuel and not the humidity of the air. not saying it didn't happen but this is the first i have heard of it.

SKR_01 · Oct 5, 2017

bobbysocks said:
i would like to see some reports or documentation about that. if a carb ices up in flight it doesn't crack and they can ice up to nearly closed. i don't understand why it would that if the ac was sitting....unless there was water in the fuel...which came from contaminated fuel and not the humidity of the air. not saying it didn't happen but this is the first i have heard of it.

VLVMA СПРАВОЧНИК ПО АВИАЦИОННЫМ МОТОРАМ 1943.djvu

rodg · Oct 9, 2017

Re shot peening. I think that the idea was to eliminate scratches due to machining, in stressed areas. Even grinding and buffing leaves scratches which could seed fractures. As an aside, I used to work for Thornycroft lorry building division. We made the Antar, much used as a tank transporter and the largest lorry built in Britain. That , and two of the smaller lorries used by the military used the Meteor engine. And very nice it sounded too. During the War, they too, made the Merlin rocker/camshaft brackets. When I started there, there were still boxes of the brackets littering the machine shops

pbehn · Oct 9, 2017

rodg said:
Re shot peening. I think that the idea was to eliminate scratches due to machining, in stressed areas. Even grinding and buffing leaves scratches which could seed fractures.

The mechanics of shot (ball) peening are complicated, from wiki.

"Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Its main application is to avoid the propagation of microcracks from a surface. Such cracks do not propagate in a material that is under a compressive stress; shot peening can create such a stress in the surface.[3]

Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, and shot coverage, shot peening can increase fatigue life up to 1000%.[2]

Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of stress corrosion.[1] The tensile stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the in the interior."

It goes on and gets more complicated but that gives the basic idea.

Bad Steel in the Rolls-Royce Merlin?

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