Welding Corrugated Pipe

The problem is with helical corrugations. But the location of the edge can be matched if both the longest and shortest points of the cuts (along the length of the pipe) are at peaks or troughs of the corrugation.

So, you need to stretch or compress the pipe until the peaks and troughs of the corrugations are at the correct locations for your cut angle, and then cut between peaks and/or troughs of the pipe diameter. There are practical difficulties in getting the helix uniform, but it can be done.

Whoops - that's not right, you would still get a mismatch between the number of corrugations on the two sides. So your join needs to be with reverse threads, just as mike k suggested.

On the other hand (pun intended), you may be able to make a short section of reverse threaded pipe that would allow you to make a pair of 45-degree joins.

I can think of two ways to reverse the thread.
You might make a cut along the length of the pipe and reverse it (turn it inside out). I think this might be tricky as the inside of the corrugations is apt to become the outside.
Alternatively, following the cut you might realign the edges so that the thread is reversed. This too could be tricky - depending on the rigidity of the material.

Of course, if you have some flat sheet you could cut it to bridge the gaps - if you could tolerate the additional disruption to the flow.

Maybe Mike K's solution of beating out the corrugation is simpler. But if that is practical, mightn't it be even better to manipulate the uncut pipe so as to produce an extremely tight bend?

If practical, make and remove several very narrow pie shape wedge cuts. Then bend the remaining pipe segments together for a not perfect, but close enough fit to do a good job of welding without having to do too much filling.

If the corrugations are parallel then yes it is possible.

If the corrugation is spiral then probably not...or maybe yes if .....

Taking a hammer and dolly to it might be quicker and easier.

Actually, there is a way that needs far fewer sections (and make a sharper turn) than Kendall's proposal.
Mostly you can turn 45^O with just a single joint; but in general the number of welded sections needed to make the bend will depend on the pitch and depth of the helix and on how far you are willing to form the edge prior to welding. The finished pipe will have continuous corrugations and the join can be reasonably tidy

I'll describe the process for a pipe with a single-helix structure - apologies that the description is somewhat gazinter.

First pre-mark the two pipes just as you would a circular pipe (of course you must also ensure that the locations of the outermost edges of these marks are at corresponding positions on the corrugation; if you have freedom of location, this would ideally be at the bases of the troughs).
Next, for each pipe section in turn, starting at the points that would be innermost on the bend, mark a new line that is offset from the pre-marking by exactly the amount as the thread of the helix departs from a cross section. By the time you have reached the outermost edge of the bend the new marks will be separated by one pitch of the helix. Now join these new lines at the outside of the bend, and somewhat parallel to the axis of the tube, such that the angles between the new line and the join are obtuse. (This angle should be the same for each of the sections to be joined). Now cut along the new line and the joining line).
Place the tubes together at the desired angle and touching at the innermost point of the bend; the ends of the tubes will line up quite well perpendicular to the relevant axis, but each will be outside the other on one side of the bend. The projecting sections are essentially curved triangles held along one edge, and should be easy to knock into line with the tube that is innermost. There may be a little spare material to trim, because the new path will be slightly shorter than the original.
Now you can make the weld.

BTW, this would have made a superb "monthly challenge".

welding galvianized metal pipe? No problem with silicon bronze. just bridge the sections. Plastic? duct tape and plastic.

Another thing I would do in this situation is to take flat plate and cut an oval ring with the id the mean id, and the od the mean od of the corrugated pipe, plus a little extra to keep the welds fillets. This would make a flange.

Sometimes it's easier to weld thin pipe to a flange than to itself, especially if the flange is a little wider than the pipe, inside and outside.

The only problem with the flange solution is how it disrupts the flow (post #4); this may not be such a great idea, particularly if the pipe is being used at full flow (even a smooth bend will somewhat degrade the local n-value)

Whether this is important will depend on the application.

had to do the same thing you mentioned for floodwater mitigation using 600 mm pipe , as you say the corrugations dont match once you change the angle.

we just welded the sections that did match , dolly and hammered the ones that didnt and silicon + hessian wrapped the whole joint on completion.

not that it mattered when a 1 in 100 year flood came the following week and washed away 40 tonnes of steel rebar , concrete and pipes overnight :)

its quite surprising how fast tonnes of straight rebar can be turned into something resembling a knotted bunch of fishing line

Just immagine how much gold is sitting in the bottom of those corrugated pipes.

If possible, lift the shorter piece of pipe and turn 180 deg. Should solve the issue