Check / consider the following:

► The upper pressure range and /or the smaller pipe diameters prompts me to investigate the possibility that the gas is reaching critical flow somewhere downstream within the pipe. When a gas gets to critical flow, sonic booms (producing vibration) are expected. In fact, one of the main means by which the additional pressure in the pipe is lost.

► If the source is a compressor, look for surging.

► If the source is a tower, look for pressure cycling in the tower

► Look at critical flow through any control valve that may be in the line.

► Are there any vapors in the line, which can condense and produce two-phase flow? Two-phase flow can cause vibration.

In chemical plant design, if we suspect two-phase flow, we instruct the piping designers to provide special anchoring.