Sele borusu tamir standında sabitlendi.

Because sele borusu is a Turkish noun compound.

In Turkish, when one noun modifies another, the second noun usually takes a 3rd-person possessive ending:

• sele = saddle/seat
• boru = tube
• boru + su = borusu

So sele borusu literally looks like saddle its-tube, but in normal English terms it is just a compound noun such as seat tube or seat post, depending on context.

This pattern is very common:

• araba kapısı = car door
• tamir standı = repair stand
• okul bahçesi = school yard

Because the full noun is tamir standı.

Just like sele borusu, tamir standı is also a noun compound:

• tamir = repair
• stand = stand
• standı = stand + compound ending

Then the locative ending -da / -de is added to that whole form. After a 3rd-person possessive ending, Turkish inserts -n- before case endings:

• tamir standı = the repair stand
• tamir standı + nda = tamir standında = on/in the repair stand

That -n- is normal after this type of ending:

• evi → evinde
• masası → masasında
• arabası → arabasında

Not exactly. Tamir is a noun meaning repair, but Turkish often uses nouns directly before other nouns to create compound expressions.

So:

• tamir standı = literally repair stand
• in natural English: repair stand

This is different from English, where we often cannot easily tell whether the first word is a noun or an adjective. In Turkish, this noun + noun pattern is extremely common.

Sabitlendi is the verb, and it is in the simple past tense.

It comes from:

• sabitlemek = to secure, fasten, fix in place
• sabitlenmek = to be secured / to become fixed

So sabitlendi means something like:

• was secured
• got secured
• became fixed in place

The ending -di marks past tense here.

It has a passive-like/intransitive meaning.

For a learner, the easiest way to understand it is:

• sabitlemek = to secure something
• sabitlenmek = to be secured

Compare:

• Usta sele borusunu sabitledi. = The mechanic secured the seat post.
• Sele borusu sabitlendi. = The seat post was secured / got secured.

So yes, it works much like a passive in English, even though Turkish learners will often meet it as a separate verb form meaning become secured or be fixed.

Because Turkish usually builds tense and voice directly into the verb instead of using a separate helping verb like English was.

English:

• was secured

Turkish:

• sabitlen-di

A lot of information is packed into one word:

• verb root
• passive/intransitive sense
• past tense

This is very normal in Turkish.

Yes. Sele borusu is the subject.

It has no special ending here because Turkish subjects are usually in the basic form (often called nominative), which has no ending.

So the structure is roughly:

• Sele borusu = subject
• tamir standında = location
• sabitlendi = verb

English learners sometimes expect an article like the or a, but Turkish does not use articles in the same way.

Because Turkish normally puts the verb at the end of the sentence.

A very common Turkish order is:

• Subject + other information + Verb

So:

• Sele borusu = subject
• tamir standında = location
• sabitlendi = verb

This is one of the most basic word-order patterns in Turkish.

Yes, Turkish word order is flexible, but changing it changes the focus or emphasis.

For example:

• Sele borusu tamir standında sabitlendi.
  Neutral order.
• Tamir standında sele borusu sabitlendi.
  Puts more focus on where it happened.

The verb usually still stays at the end in normal statements.

This is a very useful question.

• standında uses the locative ending: in/on/at the repair stand
• standına uses the dative ending: to the repair stand

So the difference is roughly:

• tamir standında sabitlendi = it was secured on/in the repair stand
• tamir standına sabitlendi = it was secured to the repair stand

In real-life technical language, these can sometimes feel close, but grammatically the cases are different:

• -da/-de = location
• -a/-e = direction/target

Because Turkish often marks noun compounds with forms that look possessive from an English-speaking point of view.

In:

• sele borusu
• tamir standı

the endings on borusu and standı do not necessarily mean real ownership like his/her in English. They are part of a standard compound-noun structure.

Then once you add a case ending, more material appears:

• tamir standı → tamir standında

So the sentence contains two very common Turkish features at once:

1. noun compounds
2. case endings added to those compounds