Richard Hed
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So what was in the water in Lybia?
Seeking info
- Thread starter sutty
- Start date
Help Support Home Model Engine Machinist Forum:
Hi Richard,
"What exactly is your definition of a "disposable tab"?, por favor."
I am not a welding engineer, so maybe my terminology is wrong:
Pressure vessel welds (as I recall from my factory days 40 years ago - in a factory where they made their own air receivers and everything else) they started the weld on a small piece of steel and ran it onto the job, then off at the end of the weld onto another tab. This was to avoid a small hole in the weld at start and end, or lack of penetration at that point. Any joint in the weld was drilled/ground-out so there was a clean "re-start" of the weld. They also used "powder" submerged arc welding along longitudinal seam welds of the air receivers - The 1/2in plate was welded in a single pass under the flux powder and in the machine stopped part way along a weld the whole job was scrapped as cheaper to scrap than repair! That was where I saw the "tabs" at start and finish of the welds. They were 2 or 3 inches long to start and finish the weld OFF the actual cylinder being welded. It maybe that length was necessary for the powder feed and wire feed separation distance. (The powder formed a normal slag - like stick welding).
I'll see what I can find about other questions.
K2
"What exactly is your definition of a "disposable tab"?, por favor."
I am not a welding engineer, so maybe my terminology is wrong:
Pressure vessel welds (as I recall from my factory days 40 years ago - in a factory where they made their own air receivers and everything else) they started the weld on a small piece of steel and ran it onto the job, then off at the end of the weld onto another tab. This was to avoid a small hole in the weld at start and end, or lack of penetration at that point. Any joint in the weld was drilled/ground-out so there was a clean "re-start" of the weld. They also used "powder" submerged arc welding along longitudinal seam welds of the air receivers - The 1/2in plate was welded in a single pass under the flux powder and in the machine stopped part way along a weld the whole job was scrapped as cheaper to scrap than repair! That was where I saw the "tabs" at start and finish of the welds. They were 2 or 3 inches long to start and finish the weld OFF the actual cylinder being welded. It maybe that length was necessary for the powder feed and wire feed separation distance. (The powder formed a normal slag - like stick welding).
I'll see what I can find about other questions.
K2
Just a nice picture...
K2
K2
Some extracts from the UK Federation of Model Engineering Societies:
Notes on the Design and Construction of Steel Boilers:
Experience shows that it is difficult to design and build a steel boiler with a barrel diameter of less than 200mm (8”). It is equally increasingly difficult to make a copper boiler with satisfactory joints over this diameter. The economics also tend to favour the 200mm/8” divide as the high price of copper has to be offset with the costs of design approval and in build inspection for welded steel.
Steel is comparatively cheap and although the plates in steel boilers are stronger they are thicker to allow for corrosion. BS2790 specifies a minimum thickness of 6.5mm or ¼”.
The design and construction of welded steel boilers is covered by BS2790.
If you are obtaining a copy of this standard be careful to check that the revision does not exclude locomotive boilers. When referring to this standard on drawings or specifications the part and revision date must be quoted.
These notes all refer to BS2790 Part 2 1973. (Refer to LATEST version, as this has been superceded!).
The formulae in all the revisions are the same but the diagrams, formula numbers and examples change together with their number.
The Euro-norm Standard for welded steel boilers specifically excludes locomotive boilers.
BS 2790 is in metric and hence Lengths are in millimetres and Pressure, Stress and Tensile Strength are in Newtons/mm2 (N/mm2).
1 Newton = 0.225lb. 1 N/mm2 = 10 Bar = 145 lb/in2
The boiler barrel should, wherever possible, be made from ASTM A106 grade B. This is hot finished seamless refinery tube as used in the oil industry and is normally easy to obtain.
The welding must be carried out by a welder who has current approval to BS EN287:2011 for the joints used in the boiler. The welding rods must be specified on the drawings and be suitable for the materials used. Certificates of Compliance should be supplied for the rods.
Fire tube should be expanded in and made from either cold drawn seamless tube which has been bright annealed or seamless copper tubes.
A comment from "the inspector": "I have seen an 8mm fire box wrapper reduced to 2mm thick in about 15 years of occasional use on a boiler which was well looked after".
In the UK: Normal service repeat testing is an hydraulic test at 1.5 x Working Pressure followed by a Steam test to ensure safety valves, pumps, etc. all work at max FIRE, and max steam pressure. - e.g. if the safety valve works OK with full blower on the full fire, but any feed pump, injector or valve does not work, then that constitutes a failure of the steam test. The initial test (to confirm the DESIGN and Construction) shall be at 2 x the NWP.
Further info:
In the US: the Hydraulic test of a steel boiler shall be at not less than 1.5 x the Maximum pressure (safety valve limit pressure). ASME for Copper boilers states the hydraulic test shall be at an equivalent pressure to the stress value limit at the steam pressure of the safety valve limit x 1.3: I.E. 1.3 x the Max pressure multiplied by the ratio of the stress limit at the temperature of the max steam pressure divided by the stress limit at 70deg.F.: e.g. At 100psi Max steam pressure (=393deg.F.) this is 2.77 times the max steam pressure = 277psi. (Max allowable stress is 6700psi at 70deg.F. but is only 3754psi at 393deg.F.).
ASME for safety valves: they shall not permit the pressure to rise more than 6% above the NWP for the boiler.
Hope this helps?
K2
Notes on the Design and Construction of Steel Boilers:
Experience shows that it is difficult to design and build a steel boiler with a barrel diameter of less than 200mm (8”). It is equally increasingly difficult to make a copper boiler with satisfactory joints over this diameter. The economics also tend to favour the 200mm/8” divide as the high price of copper has to be offset with the costs of design approval and in build inspection for welded steel.
Steel is comparatively cheap and although the plates in steel boilers are stronger they are thicker to allow for corrosion. BS2790 specifies a minimum thickness of 6.5mm or ¼”.
The design and construction of welded steel boilers is covered by BS2790.
If you are obtaining a copy of this standard be careful to check that the revision does not exclude locomotive boilers. When referring to this standard on drawings or specifications the part and revision date must be quoted.
These notes all refer to BS2790 Part 2 1973. (Refer to LATEST version, as this has been superceded!).
The formulae in all the revisions are the same but the diagrams, formula numbers and examples change together with their number.
The Euro-norm Standard for welded steel boilers specifically excludes locomotive boilers.
BS 2790 is in metric and hence Lengths are in millimetres and Pressure, Stress and Tensile Strength are in Newtons/mm2 (N/mm2).
1 Newton = 0.225lb. 1 N/mm2 = 10 Bar = 145 lb/in2
The boiler barrel should, wherever possible, be made from ASTM A106 grade B. This is hot finished seamless refinery tube as used in the oil industry and is normally easy to obtain.
The welding must be carried out by a welder who has current approval to BS EN287:2011 for the joints used in the boiler. The welding rods must be specified on the drawings and be suitable for the materials used. Certificates of Compliance should be supplied for the rods.
Fire tube should be expanded in and made from either cold drawn seamless tube which has been bright annealed or seamless copper tubes.
A comment from "the inspector": "I have seen an 8mm fire box wrapper reduced to 2mm thick in about 15 years of occasional use on a boiler which was well looked after".
In the UK: Normal service repeat testing is an hydraulic test at 1.5 x Working Pressure followed by a Steam test to ensure safety valves, pumps, etc. all work at max FIRE, and max steam pressure. - e.g. if the safety valve works OK with full blower on the full fire, but any feed pump, injector or valve does not work, then that constitutes a failure of the steam test. The initial test (to confirm the DESIGN and Construction) shall be at 2 x the NWP.
Further info:
In the US: the Hydraulic test of a steel boiler shall be at not less than 1.5 x the Maximum pressure (safety valve limit pressure). ASME for Copper boilers states the hydraulic test shall be at an equivalent pressure to the stress value limit at the steam pressure of the safety valve limit x 1.3: I.E. 1.3 x the Max pressure multiplied by the ratio of the stress limit at the temperature of the max steam pressure divided by the stress limit at 70deg.F.: e.g. At 100psi Max steam pressure (=393deg.F.) this is 2.77 times the max steam pressure = 277psi. (Max allowable stress is 6700psi at 70deg.F. but is only 3754psi at 393deg.F.).
ASME for safety valves: they shall not permit the pressure to rise more than 6% above the NWP for the boiler.
Hope this helps?
K2
Hi again,
I also found this...
Richard, towards the end of this video there are welding tabs used on the submerged arc welding machine shots showing it towards the end of a longitudinal weld. Slide 4 of attachment.
K2
I also found this...
Richard, towards the end of this video there are welding tabs used on the submerged arc welding machine shots showing it towards the end of a longitudinal weld. Slide 4 of attachment.
K2
God know's there was mentioned at the time they thought there was bugs in it that eat chrome all I know nobody would drink it (perhaps that's why they called it a sour well)
paul
You are correct in using run on and run off tabs especially with submerged arc welding on plate (you cannot use them on circ, welding of pipes, so you would overlap the finish) as the welding current (depending on filler wire dia, plate thickness and travel speed and how many wires you are using) is fairly high, power sources vary from 600A up to1250A DC and if you use multiple weld heads in the same pool then you would normally use DC + on the lead head and AC for second head and for more heads you would mix DC+ DC_ and AC This to stop Arc blow caused by the magnetic effect setup in the arc.
You cannot do full penetration root runs without using some form of backing to support the molten pool which is ok for plate welds as you can get to the back of the .plate to support it, and in the case of cylinder shells these would be carried out on a seamer using a copper backing bar (some of these are even water cooled)
For circular welds root runs are put in using TIG or MIG (you would have to put in enough passes to give the thickness to enable you then go in with the subarc) on air receivers / bulk tank carriers would have dished ends and these would be formed with a stepped lip to fit inside the shell to give you a backing bar.
Finally as with all types of welding you need to know what the requirements are for the finished component to specify what process and what procedure to be used to obtain the required result
Paul
Thanks Weldsol. I appreciate your expertise.
On Sour well water... I understood this to be strongly acidic, either from organic acids (sugars fermented with air make vinegar, etc.), or inorganic compounds such as dissolved nitrates, chlorates, phosphates or sulphates making inorganic acids. The "right" rock layers through which the water drains cause this. I looked on Goggle, and it said similar plus hydrogen sulphides, which can come from vulcanism. But I don't really know the chemistry, apart from my chemistry teacher making weak sulphuric acid by chucking some rock fragments into distilled water and a week later it was acidic.
Used in boilers will dissolve steel, also the zinc from brass?
K2
On Sour well water... I understood this to be strongly acidic, either from organic acids (sugars fermented with air make vinegar, etc.), or inorganic compounds such as dissolved nitrates, chlorates, phosphates or sulphates making inorganic acids. The "right" rock layers through which the water drains cause this. I looked on Goggle, and it said similar plus hydrogen sulphides, which can come from vulcanism. But I don't really know the chemistry, apart from my chemistry teacher making weak sulphuric acid by chucking some rock fragments into distilled water and a week later it was acidic.
Used in boilers will dissolve steel, also the zinc from brass?
K2
Weldsol, re: post #227. I understand from Federation of ME socs papers that after welding one side of the joint (obverse) the weld root needs grinding back as prep for the weld on t'other side (reverse).
For the final end plate, when you can't get to the reverse, the joint has a full penetration beyond the plate.
Any crack behind the weld will trap water and encourage corrosion, which in turn will develop stress concentrations and stress cracks so no "Un-welded gaps" are permitted. This is not the same as air receivers, so air receivers must not be used as boilers.
But I am no expert, just a "reader of rules"...
K2
For the final end plate, when you can't get to the reverse, the joint has a full penetration beyond the plate.
Any crack behind the weld will trap water and encourage corrosion, which in turn will develop stress concentrations and stress cracks so no "Un-welded gaps" are permitted. This is not the same as air receivers, so air receivers must not be used as boilers.
But I am no expert, just a "reader of rules"...
K2
Richard Hed
Well-Known Member
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What's an "air reciever"?
ajoeiam
Well-Known Member
Another name for an air tank
ajoeiam
Well-Known Member
When one is welding pipe (pressure welding) there is NO ability to grind the root a lot of the time.
This means that the root pass needs to be done right (as well as all the other passes!!!).
One of the reasons that pressure welding is 'sorta' challenging.
We are back to what is the final component to be used for as this controls how it must be welded.
Stothert & Pitt cranes back in the 70's took on a contract to supply a crane for an offshore platform, the trouble was a lot of their cranes were crawler types and did in fact contain joints using backing bars in some areas of there construction.
The crane in question was to be their standard design except instead of being crawler mounted it would fixed to the platform structure and that's where the issues come in as the crane was to be fixed to the platform it would have to comply to the welding specifications used for an offshore platform NO BACKING BARS ALL BUTT WELDS TO BE FULL PENETRATION.
So in their wisdom the draughtsman rubbed out all the backing bars on the drawing to get the drawing approved, but this now left two things one the weld prep angle was at 10 deg's and two the weld gap at the root was 3/8"
So we got asked to go in and assist them on how to achieve the required end result (which was not easy )
Paul
ajoeiam
Well-Known Member
I'd be quite curious as to how they got a 3/8" gap in the root weld done.
Care to share?
45 deg prep and 2~3mm root gap? That's just a guess from a hobby-tacker!
An air receiver is any vessel that receives and stores air above atmospheric pressure as an energy store. My Dad used a spare wheel n tyre (excuse the English spelling!), as he wanted a store at around 3 bar fed from a fridge compressor, for running-in his model steam engines. I used a 2L. coke bottle with a tyre-valve stem fitted in the cap. We both got steel cylinders for higher pressure later, but the temporary ones lasted until replaced.... They were all air receivers! Just not welded steel.
K2
An air receiver is any vessel that receives and stores air above atmospheric pressure as an energy store. My Dad used a spare wheel n tyre (excuse the English spelling!), as he wanted a store at around 3 bar fed from a fridge compressor, for running-in his model steam engines. I used a 2L. coke bottle with a tyre-valve stem fitted in the cap. We both got steel cylinders for higher pressure later, but the temporary ones lasted until replaced.... They were all air receivers! Just not welded steel.
K2
A Vatican weld? Lots of prayers and very holey?
K2
ajoeiam
Well-Known Member
That wouldn't pass any x-ray inspection!!
The Inspector for Vatican works can see everything.. and forgives many faults, but only within people, not welds.
You use the right electrode for the job one run each side until you reach a gap that you can root
Not when you put your mind to it and from memory this is how is was done and it passed NDT
Process was MMA
Consumable was 4.0 mm E7018 Low hydrogen I forget the exact amps but it would have been around 140-160 DC+
then it was a matter of bead placement and electrode angle.
We had to do a 3 foot test butt for them in the flat position there it went to NDT
It is not a job I would have wanted to do all day but there was only approx 12 foot of weld on the job but they were adamant that they would not re draw and re submit the drawings I suppose cost and time came into it as usual
see PDF to give you an idea of what it entailed
Paul
ajoeiam
Well-Known Member
OK - - - - I thought maybe, using stringer beads as outlined in your pdf, that might be what one would do.
Still a cow to do - - - me, your amperages - - - that would be for 3.2 mm electrodes - - - for 4.0 I would likely be in the 190 A range.
Need to have things 'hot' to keep that slag burned out. Even with cleaning between passes (likely wire brush of some kind) if you want clean welds with very very low to no porosity - - - you will be running HOT. (Keep a tight weld arc and the high heat isn't an issue!)
I hope that this was horizontal or flat welding - - - - vertical up would have been a serious gong show (IMO). (And for overhead - - - - find another turkey would have been my response!!!)
Isn't it amazing what the guys on the tools have to fix for the suits that can't get things right - - - lol
