What are these, and why are they on the suction head pipe?
Notice that the "shapes" are in a right angled bend where the flow changes directions.
Sometimes vanes are placed in right angled bends to reduce shock losses by reducing the turbulence of the flow as it goes through the bend.
The "shapes" the picture appear to be on the outside of the bend, in which case they have been placed there to reinforce the bend to make it stronger.
I suspect that the crescent shaped sections penetrate all the way through the pipe and are turning vanes to help direct the flow around the sharp corner.
In pipe of this size it is much easier to fabricate a mitered corner than a radiused bend and the vanes are intended to make the change in flow direction less abrupt.
In this case holes have been cut in the pipe, the vanes (probably cut from sections of pipe) pushed through and then welded on from the outside.
In this case they are pretty crude and all have the same tight radius so I'm not entirely convinced that they are doing much good.