When are thrust blocks not required?

Thrust blocks are structural components used to withstand the forces generated by changes in direction or diameter of a pipeline, particularly when under pressure. When pipes are welded at the joints, they form a rigid connection that can effectively resist these forces without the need for additional support like thrust blocks. The welded joints create a continuous structural unit that is capable of handling internal pressure and the resulting thrust, making thrust blocks unnecessary.

In contrast, the other scenarios outline situations where thrust blocks may still be needed. For instance, PVC pipes, though lightweight and strong, often require thrust blocks at bends or tees to prevent movement due to internal pressure. Above-ground pipes generally may not need thrust blocks if they are adequately supported, but they still could require them depending on the direction changes or elevation changes. Similarly, low water pressure may not eliminate the need for thrust blocks in cases where the pipeline configuration induces thrust, even if the overall forces are reduced.