Location of points on the circumference of pipe/round items

Date 11-26-2006 21:45

Many times when fabricating piping, round columns for structural applications, tanks, and other round items, it requires finding points at various degrees of position to one another. Obviously the first step in doing this is to find a reference point to start the layout from. The size of the item denotes the method of doing this in most cases. On tanks, it is likely that you will have a seam that runs linear to the tank body that you can use to locate position from the centerline of the tank. On many diameters of pipe, using a length of angle iron and laying it on the pipe so that the two legs of the angle are touching the pipe the length of it will give you an edge that you can draw a line the length of the pipe for reference.
The next step in this process requires determining the circumference of the round item. Generally wrapping a flat tape around the item and coming up with a measurement is a good first step. Once you have this done, use the number that you have, convert it to inches and a decimal and then divide this number by 360 to determine the running distance for each degree increment from the reference point.
Now if I needed to locate something 35 degrees from the reference line I would multiply the single degree increment by 35, and using the product from this equation, after converting it back to feet, inches, and a fraction, as required, I could measure from the reference line at each end of the round shape to mark two points, using a chalk line I could snap a line between these two points. I would then measure from the end of the round shape to the appropriate length or elevation and mark this point to locate whatever item belonged there. There are many variables to this process, I believe I've given folks a little bit to think about here and hopefully it will help some of you when facing this sort of scenario. Regards, aevald

By MNSTRBLDR (**)

Date 11-27-2006 13:05

aevald, Good tip. I use this alot. I learned it for laying out nozzles on tanks, but I have learned you can use this for cutting down pipe fittings too. The formula I use is: diameter x pi / 360 x desired degrees. Like you said, as long as you have starting point you can measure from it around to that degree. It's hard to explain without doing it hands on huh? Henry

By aevald

Date 11-27-2006 14:40

Hello Henry, yes, it is somewhat difficult to explain this one. You're also right about using the diameter x pie portion of the equation, one of the reasons that I didn't mention that, is that many times the end of the pipe or round shape isn't very round so when a person measures the diameter that way it can have an adverse effect on the correct layout. Many thanks for bringing that up. Regards, Allan

By 357max

Date 11-27-2006 15:39

To lay out a pipe with four divisions. Wrap a tape (paper dry wall tape is very good) and determine the circumference length. Fold the length of paper in half and then fold the two ends into the middle to have four divisions with no math. To divide into three parts fold the paper's ends towards each other and overlap so both ends are overlapping each other equal length.

By aevald

Date 11-27-2006 15:46

Nice tip 357max, I definitely hadn't thought of that one. Regards, Allan

By jwright650 (*****)

Date 11-27-2006 17:13

When we lay out pipe columns, we use a centerfinder that comes with a combo square set, divide the pipe into fourths to locate the four faces. Sometimes we even use a template made from template board to help the fitter layout odd skews off of the centerline of any of the four faces.

By MNSTRBLDR (**)

Date 11-28-2006 13:16

Yeah, if we lay out saddles on pipe, we will use adding machine paper and divide it into 4ths,8ths, etc. When our sheetmetal guys lay out tank legs and floor nozzles, they lay them out on thin sheetmetal, cut them out, and roll them to sliade over the pipe and trace. I guess I was thinking more about tanks. Good tips! Henry

By monsoon12 (**)

Date 12-23-2006 14:45

Ive always found a wrap around does a really great job for laying out pipe.It has all the measurements on it .Of coarse you have to find your starting point.I use a square to find center of the pipe.Just butt it up to one side an what every the o.d is i spilt in have.So if its 4 1/2 od my center is 2 1/4.Then i use the angle method to lay the line out.It helps also to put the base plate on first if your doing colums.This gives you 4 sides to rotate equally the peice.Thus makes it easier to find the four centers of the pipe.

By monsoon12 (**)