Function of the alarm hole for the boiler tie rod φ5

I encountered this before; the alarm hole was positioned incorrectly at that time, and it wasn’t detected after welding it to the tube sheet. Water started seeping out from there during the hydrostatic test. I think the pull rod is subjected to alternating stresses during operation, which can easily cause cracks at the welding points; this serves as an alarm mechanism.

It seems that according to the strength calculations, the depth of the alarm hole must be at least 15 mm into the tube sheet; this is probably related to the fact that the tube sheet itself cannot provide sufficient support. I’m upvoting this post; I hope someone with more experience can give some advice, as I’m curious too.

I guess that, while the boiler is in operation, the tube sheet is subjected to alternating stresses. The tie rod with a φ5 warning hole, relative to its weld seam, is prone to developing cracks in the section of the tie rod located within the tube sheet. When water seeps out from there, it indicates that the tube sheet has lost much of its strength, and the weld seams have also developed extensive cracks! By this point, this furnace has already reached the end of its useful life! The following is just my personal speculation!

A beer factory in our district purchased 3 KZL4-13-AII steam boilers from another province to meet its production needs. After the boilers were installed, a hydrostatic test was conducted in accordance with relevant requirements; during this test, it was found that water was spraying out from the warning holes of the strut rods connecting the front and rear tube sheets of 2 of the boilers. As a result, the hydrostatic test failed. Upon opening the boiler drum for inspection, it was discovered that the strut rods had completely broken, with the break occurring at the root of the weld where the strut rod connected to the tube sheet. Macroscopic and electron microscope analysis of the fracture surface of the tie rod revealed distinct fatigue fracture characteristics, with the crack origin located at the lower part of the fracture surface ； Furthermore, inspections revealed that the welding quality of the tie rod was poor; a large amount of slag inclusions, lack of penetration, and undercutting were found at the root of the welds. Metallographic examination of the structure near the fracture surface of the tie rod showed severe non-metallic inclusions. Based on the above inspection results, the analysis of the causes of the rod fractures reveals that the base material of the support rods in these two boilers contained severe inclusion defects. The welding quality between the rod heads and the tube sheets was poor, and circumferential undercutting, incomplete welding, and slag inclusions at the root of the welds were the underlying factors that led to the formation and propagation of fatigue cracks.