This is the inside of one of my headers:

[c_dug]

https://i235.photobucket.com/albums/ee81/paddy2007dug/pipe%20scratches._zps10jed0hx.jpg

Those lines at the back are grooves in the metal, I happened to spot them when I was refitting the exhaust today. They're mostly along the outer edge of the first bend in the pipe from the header, and to a lesser extent the inner edge too.

Just curious what's caused them? Is it just the bending of the pipe in manufacturing or has it been blasted to buggery by something coming out of the combustion chamber?
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Howling Terror]

Don't know. Great photo.
____________________
Diabolical homemade music Bandcamp and Soundcloud
Singer songwriter, Artist and allround good bloke Listen to Andrew Susan Johnston here
The Harry Turner Project

[Gazza M]

From bending I reckon. Is that bend the tightest one? I think when they are made they come out slightly elliptical - the tighter the bend the more so they are. So the metal is creasing up around the tightest radius part of this - outside of the bend on the ID.

At least his makes sense in my head
____________________
Past: '07 YBR125, '00 GPZ500S, '99 ZRX1100, '98 CBR600 track bike, '97 ZX9R
Present: '05 R6 track bike, 140 pit bike

[Matt B]

It's like one of those photos where you have to guess what it is.

I would never have said inside an exhaust header.
____________________
stinkwheel: He had an animated .gif of a cat performing fellatio. It's not socially acceptable. It can have real life adverse effects on other people.

[ZRX61]

Just marks from manufacturing.
____________________
They're not one night stands, they're auditions.

[carlosvalderr...]

They're mandrel marks, nothing to worry about. The mandrel sits inside the tube like a snake and stops it collapsing as it's bent. Thin walled tubing is particularly susceptible to it.

You have amazingly clean headers BTW.

[Vincent]

I'd guess that they are extrusion marks from when the pipe was going throgh a stretched reduce mill for sizing during manufacturing.

"Stretch marks" in other words
____________________
Space Is Deep

[c_dug]

Thanks for the replies. Don't be decieved by the cleanliness, they've been on the bike for less than 2 months, ~2000 miles, they've barely had a chance to get dirty on the inside!
____________________
I am a bellend, I am a man of constant sorrow, I am a gummy bear, I am a rock.

[Vincent]

Nice photo Reminds me of "Logans Run"
____________________
Space Is Deep