To make a pipe bomb you need only a few ingredients, most of which are commercially available and cheap. The following are instructions.

1. Acquire a metal pipe in, the pipe should be threaded at both ends if you wish to avoid using welding equipment on an explosive. If it is not threaded, thread it yourself. If you cannot thread metal pipe then stick to PVC tubing, less fragmentation and lower blast wave but a decent alternative.

2. Acquire 2 end caps that can be threaded onto the pipe, put teflon tape onto the threading to increase effectiveness.

3. To absolutely maximise the results weld the caps shut after fitting the caps on, since it's teflon sealed the explosive shouldn’t be detonated by a stray spark from the welding. This should be done as late as possible to allow for repairs, maintenance, bug fixing, etc.

4. Decide on the detonation mechanism

4.a. The two simplest designs are a light sensor and a timed detonation, the former can be done easily if you put a light sensor on the body of the bomb and squeeze a wire through the threading leading to the explosive, then attaching a battery and adding a simple logic condition that makes it detonate only the second time it sees light, that way you have time to hide it and not detonate.
4.b. The second method is entirely sealed and is unfortunately the simplest to defuse, to use this method you only need a battery powered stopwatch and several diodes to create a higher amperage with the same output of energy, this is so that you can actually electrically detonate the explosive. This method is dangerous because any mistake in the wiring can and will cause detonation.
4.c. The more complicated method is a remote detonation, this can be achieved via a cheap old cell phone. Old Nokias and the like have a wire that leads to the speaker, and the speaker is triggered when receiving a phone call, thus triggering the explosive
4.d. Alternatively, you can combine this into a 2-in-1 combo by making it either remote detonated or timed and then adding a light sensor on the inside such that any attempt to remove the caps end in detonation
4.e. Footnote: all of these methods rely on electric detonation, something that not all explosives are capable of. Test your explosive’s electric responsiveness before using these designs, or if the explosive is susceptible to thermal detonations then you can simply add a heating element to replace the electric detonation with a thermal one.

5. Manufacture the explosive, this can be either the simplest or the hardest parts of the process depending on the explosive used, things such as NCl3 are incredibly dangerous and time consuming to make, whereas PETN is simpler in terms of safety but more material, equipment, and experience intensive intensive.

6. Screw one of the end caps onto the pipe and weld it to the main body; welding is not necessary but recommended. Pour/place the explosive into the pipe, making sure to leave enough space for the detonation mechanism.

7. Insert the detonator of choice and make sure to activate it then screw the second end cap shut. Once again, make sure to weld for maximum results.

8. Decide on where to place the pipebomb, if it is meant to kill a human then the best place to put it is in a place that is close to the target, i.e., mailbox, desk, or any kind of box that needs to be picked up and opened. If the pipe bomb is meant to destroy foundations and supports then changing the pipe bomb into a shaped charge warhead, the best method would require a cone of copper, but wine bottles work just as well, even without an end cap. Alternatively, you could make several duds, and sprinkle them mixed with real ones around an area. However, make sure not to get caught whilst doing any of this.

9. I am a legal citizen, I have not committed a single crime worse than jaywalking in my life; this is all an advanced thought experiment on my behalf.