Опрессовка закончилась без протечек.

Опрессовка is a technical noun. It usually refers to pressure testing of pipes, a heating system, plumbing, or some other sealed system.

It is not an everyday household word for most learners. You are much more likely to see it in:

• maintenance reports
• utility notices
• engineering or construction contexts
• housing and plumbing discussions

It comes from the verb опрессовать / опрессовывать.

Because закончилась agrees with опрессовка, and опрессовка is a feminine singular noun.

So in the past tense:

• masculine: закончился
• feminine: закончилась
• neuter: закончилось
• plural: закончились

Since опрессовка is feminine, the verb must also be feminine:

• Опрессовка закончилась.

The -сь is the reflexive ending, a short form of -ся.

In this sentence, закончиться means something like:

• to end
• to come to an end
• to be over

So:

• закончить = to finish something
• закончиться = to finish / end on its own

Compare:

• Рабочие закончили опрессовку. = The workers finished the pressure test.
• Опрессовка закончилась. = The pressure test ended.

So the reflexive form is used because опрессовка is the thing that came to an end.

Yes, Опрессовка кончилась без протечек is grammatically possible.

But закончилась often sounds a bit more neutral, standard, or formal.
Кончилась can sound slightly more conversational.

In a technical or official context, закончилась is usually the more natural choice.

The preposition без always requires the genitive case.

Also, here the meaning is without any leaks, so Russian naturally uses the genitive plural:

• nominative singular: протечка
• genitive singular: протечки
• genitive plural: протечек

So:

• без протечки would mean without a leak in a singular sense, which is not the natural phrasing here
• без протечек = without leaks / with no leaks

That is the standard expression.

The dictionary form is протечка.

Here is the relevant pattern:

• протечка = a leak
• протечки = leaks / of a leak
• протечек = of leaks

In this sentence, протечек is genitive plural because it follows без.

They are close in meaning, but not exactly the same in structure.

• Опрессовка закончилась без протечек.
  = The pressure test ended without leaks.

• Во время опрессовки не было протечек.
  = There were no leaks during the pressure test.

The first one presents the whole event and its successful outcome.
The second one focuses more directly on the absence of leaks.

Both are natural, but the original sentence sounds compact and report-like.

It sounds neutral-to-formal and somewhat technical.

A sentence like this would fit well in:

• a maintenance report
• a utility company notice
• a building management update
• technical documentation

Because of the word опрессовка, it does not sound especially casual.

Yes. Russian word order is flexible, though the original order is very natural.

Possible versions:

• Опрессовка закончилась без протечек.
• Без протечек закончилась опрессовка.

The first version is the most neutral and straightforward.
The second version puts more emphasis on без протечек.

For a learner, the original order is the best default choice.

Yes, the stress is useful to know:

• опрессо́вка
• закончи́лась
• без проте́чек

A rough pronunciation guide:

• опрессо́вка = oh-pre-sohv-ka
• закончи́лась = zuh-kahn-CHEE-lahs
• проте́чек = prah-TYE-chek

As often happens in Russian, unstressed о is pronounced closer to a.

That is understandable, but it is less natural in this context.

Опрессовка закончилась без протечек sounds like a normal summary of the result.
Опрессовка была без протечек sounds less idiomatic, because была simply means was, and Russian usually prefers a more event-based verb here, such as закончилась or a phrase like прошла без протечек.

A very natural alternative is:

• Опрессовка прошла без протечек.
  = The pressure test went without leaks / was carried out without leaks.

Both can work, but they highlight slightly different things:

• Опрессовка закончилась без протечек.
  Focus: the test ended without leaks.

• Опрессовка прошла без протечек.
  Focus: the test went / proceeded without leaks.

In practice, both are natural in reports.
Прошла без протечек can sound especially natural when describing how an operation or procedure went overall.