The Devil’s flesh light - a mineral spa feed pipe from a thermal geyser

As it's written, the sign means this:

This pipe showcases an upward-facing structure composed of an unnamed mineral. Said structure has been in place for six months, and it must be replaced twice a year.

What they meant was this:

This pipe demonstrates six months of mineral buildup. Pipes must be replaced twice a year.

"Build up" is a verb when it's two words. The same goes for any term composed of an action followed by a direction (as with "log in," "shut down," or "stand by"). The one-word versions are the nouns.

The other error – that of applying "requires" to "mineral buildup" instead of "pipe" – occurred because the writer mistakenly assumed that the the comma would delineate the two nouns. The trouble is that we already have a predicate with "demonstrates," and "requires" is thus applied to the second noun (with or without a comma).

Another (correct) way to write the sign would have been as follows:

This pipe (which requires replacement twice a year) demonstrates six months of mineral buildup.

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