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Derrick rates
Went to a Drillers' meeting yesterday and the subject on limits/certifications of different rigs was addressed. I asked a question that couldn't truely be answered. Why is a mast rated differently from 10 lines to 8 lines?
Now, I have been running rigs for some time and have seen this before. I understand the difference in line pull and the learned about simple machines in the 4th grade but, why would a derrick that is gunna collapse at 550k on 8 lines hold up 575 on 10? Seems that the only thing changed on string up would be effecting the drawtool and anchor rates. I would think that whatever the indicator reads is what is on the rig.
Now, I have been running rigs for some time and have seen this before. I understand the difference in line pull and the learned about simple machines in the 4th grade but, why would a derrick that is gunna collapse at 550k on 8 lines hold up 575 on 10? Seems that the only thing changed on string up would be effecting the drawtool and anchor rates. I would think that whatever the indicator reads is what is on the rig.
Replies to This Discussion
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Permalink Reply by T L Strickland on -
Let's say a rig is rated at 220k on 6 lines 330k on 8 lines 440k on 10 lines.
I will let you in on the majority of the two reasons.
1rst no line of any kind should ever be subjected to more than 50- 60k single line pull.
Simple math shows you 2 x 50 is a 100k, so on and so forth. Although workover and drilling rigs are much different, k a drilling rig may be bolted or not.
Yes a workover rig has drum saddles welded to the frame of the carrier.
On a workover or mobile rig,your derrick or a derrick and sand drum combo is the majority of the weight of the rig, so the stringup shifts the pull and breaking drag to the mast, instead of the drum, if you could pull 5ook on a single line, then you would have a stright pull and your clutches and brakes would fail almost immediately.
But for every line you add you double your strength in pull or braking.
unless you are with a nice company who lets you run double fast tied back into the drum.
then your computations will come out differently.
Because 6 lines is just that 6 lines connecting blocks and crown, a single line to drawworks, and a single deadline tied to an anchor.
On a workover rig you can run 6 lines proper, like mentioned above.
Or 5 lines( which is 6 line stringup, with no deadline, and two fast lines in the drum of drawworks.)
So this is where on workover and light mobile drilling rigs u come up with some weird numbers.
6 lines 160k, 8 lines220k or 6 lines 250 and 8 lines 330k etc. Always remember that on a double fast take 50k out of your figures when running double fast line.
It has more to do with Blocks,bickets,reeling assembly(crown/ and draw works)
Secondly....is shock loads, not just hook loads. if you have a full stringup on a derrick, you have no open sheaves on the crown and the odds are your block speed is slow enough that it is easy to be smooth.
plus the stringup on the rig is also, a reminder not only that the line should not be subjected to a straight line pull exceeding 50 k, but your brakes and clutches should not either.
`I am sure you have noticed that most drawworks just sit on the sub, no pins no bolts . most drawworks weigh less than 50k. even if a drawtool is bolted/pinned in place, 5ok at the drum is going to screw some things up if you are not careful.
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Permalink Reply by Jay Brown on -
I think you missed the point, or the question. This isn't something that pulls sucker rods. I was asking why it makes a difference to real jack knife derrick what it is strung up on. This drawworks/compound/engines weight is just shy of 80k.
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Permalink Reply by T L Strickland on
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Well no offense....but you have to understand the same principles apply to both....i have built 2500 hp drilling rigs...and I have built workover rigs.
The 50 k figure I gave was with either 1 1/8 " swaged or 1" hammered drilling line.
Bigger diameters can take more.
The rating on the derrick....ok if you have an api tag. it tells you your ratings per line....the reason is this liabillity, if they just put on the tag that the derrick has a 550k static hook load rating and don't put any guidelines on what kind of string up there is needed to pull the load.....then you guessed it some dumb butt would find a way to think he could pull 55ok on 6 lines....then guess what he pulls things in 2 and kills somebody.
You have to realize that sucker rods, tubing, drill pipe and drill collars all get out of the hole the same way.....hanging off the bottom of the bicket and bales on the bottom of the blocks.
Same principles, same logic, just different rigs and materials.
FYI I have drilled and run workover rigs, I used to run a 900 Cabot mobile double drum workover rig/drill rig that had a 114' 550,000 # shl derrick on it.
I've run an 80 b national with a 1.5 million pound covco derrick on it....a rig is a rig, same principles behind all of them. SUCKER RODS have nothing to do with it, I really get irritated when people get biased like a workover rig is a water rig or post hole digger or something.
I guess if you want a better engineering answer you can send an email to cleon sheldon the design engineer for nabors who left national/cabot/franks after 30 years...he is a great friend and ex coworker of mine when we were designing the millenium rig and the new e and ec style drilling rigs when I was the district manager over there in the barnett shale and in west texas.
Second half of the example is, lets ask have you ever seen a rig that was light on the tail end especially a big box on box sub, meaning when you come off the headache to raise the derrick, or when you are laying the derrick over to rig down, it is trying to lift the drawworks and back end of top sub....so you snub the back end down to a winch truck or the pumps when you rig up or down. Thats leverage alone. the same thing applies if you are running to light a string up.
If you are strung on 10 lines pulling 500,000, the odds are you have 30-35k straight line pull at the drawworks, if you had less lines and you were pulling over the weight of the drawworks you would be breaking crap or cratering a sub and derrick.
It is all about hoisting power and breaking power...the tag and guidelines on stringup are merely an attempt to make operations idiot proff and to circumvent liability in a litiguous society.
I didn't miss your point....you just got the answer to the question on stringups and why....you just did not realize it actually has less to do with the derrick as it does have all to do with wire rope safety and braking.
It's just like comparing it to your car, take the front brakes off and see how much braking power you lose, then pull half the spark plugs and your horsepower matches your braking power. Put them back like it was designed to operate and it's great.
I guess my point is yeah it's nice to understand why they do and say to do things a certain way.. but the fact of the matter is it doesn't matter why...all that matters is there are lots of good reasons why they establish s.o.p's and give guidelines to work by.
Happy holidays
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Permalink Reply by Curtis on -
Thought this mightbe a good place to post some pics-I actually don't understand enough about the discussion to contribute.so while we are talking about derrick loads I will share these...
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Permalink Reply by Shawn Kern on -
Rod Ric Rig 10 they got stuck on the way out and pulled the derrick over. Was working for them on a different rig when this happened.
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Permalink Reply by T L Strickland on
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I have seen pictures of both rigs before, we got safety bulletins of the one rig when I was with Nabors, a truck pulled into location and caught a guy wire causing the derrick to buckle and causing a fatality on the rig.
Another interesting point that will confuse people more... is when I tell you that any derrick built to api specs with T1 or better grade steel( which is all with API Certification) are engineered and rated with a 2:1 safety factor, meaning tags are rated lower than actual engineering.
Last but not least any derrick more than ten years old per government guidelines and api standards should never be used to pull more than 80% of rated capacity.
One other crucial point worth making is when someone tells you that a derrick has been inspected and recertified to origonal capacity.
This is impossible, I have refurbished over 150 rigs, you can never recertify a derrick.
A derrick get's certified one time....when it is new.
All that this new inspection(so called certification means is a structural engineer) Visually inspected the derrick and found it to be in safe working order...with no recommendations on max capacity or minimum capacity.
Furthermore....in few very rare cases a company and engineer will do NDT testing(non destructive testing) using sonic testing,xrays, and magnetic as well as flourescent dye testing to make sure there are no cracks or crystallized sections in the derrick, allthough this thorough of testing is very very rare.
99% of testing entails a inspection of the mast in current condition, then a secondary inspection on completion of sand or media blasting, then all areas in question if any, and yes there is always areas of concern, are marked for repair on the mast and a blue print, then repairs are made, then a final inspection will be performed to approve of the repairs, including the engineer and the welders and suppliers providing a statement of origin and a statement of proff of the grade and age of the steel and welding rods used in the repair of the mast.
At this point is when two sets of blueprints are made, one which is as found( before repairs) one set is as built or as left( after repairs). These must be forwarded to the insurance carrier for the rig, and must be kept in a rig file for that rig, because any accident of any kind on a rig, especially a fatality or debillitating work comp injury, the lawyers will ask for all the maintenance files for the life of the rig, and qualifications of the people who manage and maintain the rig. This is where the importance of records and using ISO 9000 and API certified contractors or vendors is important!
Sorry I was short in my previous post!
Happy holidays everyone!
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Permalink Reply by Curtis on
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Haha...my drawworks have always had 8 BOP Bolts that I am constantly checking with a Hammer Wrench. Drillers Console sits on the same skid, and I was always worried about going North when picking up off bottom
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Permalink Reply by Jay Brown on
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As I've stated, I am aware of the basics of simple machines and understand the limits of everything down stream of the derrick. This sub is limited at 850k (RT + SB). Drilling line is 1 1/4" EPIC (somebody may correct here).
This isn't a company rateing or limit, asked nothing about line size, and I realize the diff in string ups and don't care to here a rendition on why you string up on 10 lines. This is a rate that comes from LCM. When a bare mast is sitting in the yard, no crown, no blocks, no rig, no nothing, it has a load rate. It cares nothing about the brake handle passing the A frame. It has a 8 and 10 line rate and it is for the welded up iron sitting there. I understand the number for "wires and tires" because of the multiple options. That I'm pretty sure is "rig" rates. Maybe I do need that engineer's address.
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Permalink Reply by Lynn Neighbors on -
The 1,025,000 is the Gross Nominal Capacity weight of the mast (on my rig), traveling block, hook and drill line.We do not use this rating any more. To change the GNC to static hook load, you can multiply the GNC by 12 lines .75, 10 lines .71, 8 lines .67. Many masts have been pulled in by persons that do not understand the GNC capacity.
The paragraph above came in an E-mail from Superior Derrick. Since then i have moved to another rig, but the deal was at the time that the plack on the derrick was a rating for 12 lines and we only used 10. You must know the weight of your mast, blocks, drill line and multiply by the right percentage to arive at the right number. As far as what is showing on the wieght indicator, it will only hold true if it has been pumped up and is working properly, plus the weight indicator dial is calibrated for a specific number of lines. If it is set for 8 lines and you string up on 10 it is going to be incorrect.
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Permalink Reply by Tony Ackerman on -
Nice explanation of static hook load Lynn, but I'm not sure that it answers Jay's original question "Why is a mast rated differently from 10 lines to 8 lines?" Maybe I'm misunderstanding his question, but the ability of the mast to support an amount of weight doesn't change from 8 to 10 to 12 lines; it's a static device and it's capacity remains the same.
Isn't static hook load is a rating of the whole active lifting mechanism, i.e. prime movers, draw works, crown and traveling blocks? Each of those pieces gain mechanical advantage with the increased number of strung lines, so each is capable of lifting more (though at a slower rate). However the mast itself doesn't gain any mechanical advantage with more lines. At some point the active components would be capable of pulling more weight than the mast is capable of supporting.
Jay, I may be reading your question wrong and if I am let me know; apologies in advance. If I am reading your question right, I too am stumped on why the mast would be rated differently for different line configurations. Maybe the mast rating is meant to represent the whole system rating?
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