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Frequently Asked Questions
What does an end cap protect?
The outside of the pipe end, and the bore behind it.
Most often that is a thread or a machined weld bevel.
It also closes the bore against ingress.
Those two duties can conflict.
A cap gripping a thread must not damage it.
One intended only to keep debris out can be looser and simpler.
Why are threads the priority?
Because a damaged thread will not make up.
Re-cutting needs specialist equipment on pipe of any size.
Sometimes the length is scrapped instead.
Caps that engage the thread protect it better.
The thread is then supported rather than exposed under a loose cover.
It is the most expensive small area on the whole length.
How easily are weld bevels damaged?
Very, and less obviously than threads.
A bevel knocked out of shape has to be re-prepared.
A nicked edge produces defects in the root run.
Those show up at inspection rather than at the time.
Bevel protectors are made specifically for that geometry.
Re-preparation on site is slower and less accurate than the original machining.
Why cap pipe during storage?
Because open pipe collects water, sand, grit and animals.
Cleaning a long run afterwards is far harder than capping it.
Debris left inside damages pumps, valves and seals.
Standing water causes internal corrosion.
In hydraulic, instrument, oxygen, food and pharmaceutical systems it is a documented requirement.
Cleanliness certification frequently depends on ends never having been open.
Do they survive outdoor storage?
Only if specified for it - ultraviolet exposure makes many plastics brittle.
Pipe frequently sits outdoors for months.
A brittle cap falls off or shatters.
The protection then ends silently long before anyone checks.
UV-stabilised grades are specified for extended storage.
Periodic inspection catches caps that have already failed.
Cap or plug - which do I need?
A cap goes over the end; a plug goes into the bore.
Caps protect external features like threads and bevels.
Plugs protect internal threads and bores.
Both close the bore against ingress.
Which suits depends on what is on the end.
Male threads take caps; female threads take plugs.
Must they be removed before welding?
Always, and it is worth stating because it does get missed.
Plastic near a weld melts and contaminates the joint.
It also produces fumes hazardous in confined spaces.
Bevel caps sit exactly where the weld goes.
Checking the bore is clear before closing a system is the same discipline.
Counting caps off is used on critical pipework for that reason.