Two days ago, a customer from a power station called, and his tone was very urgent, saying that a corrugated expansion joint on their pipeline was leaking and perforated. Asked me if I could just weld it on and make do. This kind of question is too common in the industry, but the answer is really not simply "can" or "can't". What about perforated metal expansion joints? Whether it is repaired or replaced depends on the reason and location of the perforation, and which expansion joint you are using. Let's talk about the conclusion first: blind repair welding will in all likelihood happen bigger things.
The reasons for perforation vary
The most common is corrosion-chloride ions, sulfides in the medium, or high-temperature oxidation. For example, the corrugated expansion joint used in the power station industry is prone to high-temperature oxidation and thinning on the outer wall under high-temperature flue gas for a long time, and finally perforation. Where is the metal corrugated expansion joint in the cement industry, dust abrasion is the main cause. In another case, the tie rod nut is not adjusted properly during installation, which causes the bellows to bear undue torsion or lateral displacement, and fatigue cracks eventually develop into perforations. Think about it, if you weld indiscriminately, there are still media residues sandwiched in the cracks, and it will be virtual when welded.
By the way, there is another reason for perforation that many people ignore-the deflector failure. The specific function of the expansion joint guide tube is to protect the bellows from high-speed medium erosion. Once the guide tube is damaged, the medium directly impacts the bellows, and the local erosion speed can be several times faster. At this time, even if you weld the perforation, the inner wall will continue to thin, and it will leak again soon.
Is there a temporary emergency solution? Yes, but the conditions are harsh
For example, the circulating water pipeline with low pressure and normal temperature has a small perforation (the diameter does not exceed 5mm), so it can be temporarily blocked with a rubber gasket covered with a fixture, or cold solder (metal repair glue) can be used for emergency response. But only if you have to confirm that the medium temperature does not exceed the temperature resistance range of the glue, and the pressure is below 0.5MPa. Don't do this on high-temperature and high-pressure steam pipelines-steam pipelines belong to pressure pipelines, and they can be repaired and welded directly after perforation. Local stress concentration may make the bellows explode.
Many people think that the expansion joint and the compensator are two different things, so they treat them according to the ordinary pipeline repair welding process, and as a result, the elasticity of the corrugation is welded away. Actually, is the expansion joint the same as the compensator? The answer is one thing, it's just called differently. The bellows itself absorbs displacement by elastic deformation, and the welding repair area will harden and lose elasticity, so this expansion joint is basically wasted.
When do you have to change? Don't hesitate to replace it with a new one
Let's put it this way, as long as the diameter of the perforation exceeds 1/3 of the wall thickness of the bellows, or the perforation appears in fatigue sensitive areas such as peaks and troughs, don't hesitate to replace it with a new one directly. EspeciallyLarge diameter thick wall expansion joint、External pressure single axial expansion jointFor those with high pressure, the weld area will become a new weak point after repair welding, and the risk of creep fracture will double. Also, if the perforation is associated with damage to the guide tube, it must be replaced as a whole. Once the guide tube is broken, the internal erosion will be accelerated, and the welding repair is a waste of effort.
And guess what? Some customers feel that it is expensive to replace the expansion joint, so they have to repair welding to save money. As a result, it took two days. On the third day, the weld cracked, and the medium sprayed out and almost injured people. The loss of one equipment shutdown is much more than replacing the expansion joint. Safety first, don't gamble on your luck.
Prevention is more important than remedy
Corrosive medium, preferredPTFE-lined hoseOrPTFE compensator； High temperature flue gas pipe, forHigh temperature axial expansion jointInner lining with temperature-resistant coating; Dusty cement line, useMetal Corrugated Expansion Joints in Cement IndustryOrRectangular non-metallic expansion joint(the kind of fabric fiber), the latter is low replacement cost and convenient maintenance.
The direction of the arrow of the expansion joint points to the direction of the medium flow, and the tie rod (the role of the expansion joint tie rod is to limit excessive tension) can only be loosened after the pipeline pressure test. In daily inspection, check whether there are rust pits and peeling on the corrugated surface, and cooperate with the inspection cycle of non-metallic expansion joints, at least twice a year.
Metal expansion joint perforation, don't treat it as an ordinary leak. It is like a spring. Welding repair is equivalent to tying a knot on the spring. Do you think this spring can still work properly? Leave professional matters to professional people-if you are unsure of the cause of the perforation, or are unsure whether it can be repaired, contact the manufacturer directly to send the on-site photos and media parameters.