In the polyolefin anti-corrosion layer, the failure modes of different types of anti-corrosion layers are different.

      Sintered polyethylene has exposed a lot of bonding failure problems during operation. Then, although some reports indicate that the occurrence of bonding failures is very common, there are very few reports of owners on the presence of significant corrosion under the failed corrosion protection layer. A large number of laboratory tests have shown that corrosion control is still effective under the FBE anti-corrosion layer that has lost adhesion, which may benefit from FBE allowing partial protection current to flow to the surface of the steel pipe. The emergence of a large number of FBE adhesion failure problems has led to the widespread use of other types of polyethylene anti-corrosion coatings.

      For the double-layer polyethylene anti-corrosion layer, the 2PE with horseshoe fat as the primer is prone to the problem of drip of horseshoe fat under warm environmental conditions. Another report introduces that after 20-30 years, the horseshoe fat is oxidized. It becomes a loose and brittle powder, which causes water to penetrate into the corrosion protection layer and cause corrosion. This is due to the insulating properties of extruded polyethylene, which prevents the cathodic protection current from entering under the corrosion-resistant layer that has lost adhesion. Low-density polyethylene anti-corrosion layer pipelines have stress cracking of the anti-corrosion layer. Such cracks are easily caused by small damage or scratches on the anti-corrosion layer. In the most serious cases, the entire pipeline is affected by cracking, but it is reported that this extreme The reason for this is due to the lack of material specifications. 2PE using hard adhesive as the primer also has the problem of adhesive losing adhesion to the substrate and delaminating with polyethylene. The anti-corrosion layer also cracked, causing water to penetrate under the non-stick anti-corrosion layer and cause corrosion.

      The three-layer polyethylene anticorrosion pipeline has also exposed the problem of adhesion failure within a few years of commissioning. It is reported that several pipelines have been in use for less than two years. The extent of the problem is different. The lighter one is that the corrosion resistance of the coating is reduced and can be easily peeled off, but the substrate is not corroded. The most serious is that the corrosion layer is completely separated from the substrate, and corrosion products are formed on the metal surface. However, the cause of the problem is usually the quality of the paint. Active corrosion was even found under the anti-corrosion layer on the new pipeline, but these 3PE anti-corrosion layers use low-density polyethylene. The cause of corrosion can be attributed to higher oxygen permeability and water permeability; the three-layer anti-corrosion layer also Stress cracking occurred, and the cause of the cracking of the anti-corrosion layer was also a small scratch on the outer anti-corrosion layer. PE material and anti-corrosion layer aging, failure-related properties include: 1, cracking and embrittlement caused by ultraviolet aging. 2. Stress cracking. 3. The permeability of water and oxygen.

聚烯烃防腐的失效问题

      在聚烯烃防腐层中，不同种类的防腐层的失效形式是不一样的。

      熔结聚乙烯在运行使用暴露了大量黏结失效问题。然后，尽管有些报道反映黏结失效的产生很普遍，但却很少见有业主方面关于失效防腐层下存在明显腐蚀的报道。大量的实验室试验表明，失去黏结的FBE防腐层下，腐蚀控制仍然有效，这可能得益于FBE容许部分保护电流流到钢管表面。FBE大量黏结失效问题的出现导致了其他种类的聚乙烯防腐层的广泛应用。

      对双层聚乙烯防腐层而言，玛蹄脂为底胶的2PE在温暖环境条件下易出现玛蹄脂下淌的问题，另有报道介绍，经过20-30年，玛蹄脂被氧化，变成疏松而易脆的粉末，导致水渗入防腐层产生腐蚀。这是因为挤出聚乙烯的绝缘性质，导致阴极保护电流无法进入失去黏结的防腐层下得缘故。低密度聚乙烯防腐层管线出现了防腐层的应力开裂，这类开裂容易由防腐层上的小损伤或划痕引起，最严重时，整条管线都受到开裂的影响，但据悉，这种极端情况发生的原因归结于材料规范的缺失。使用硬质黏结剂作底胶的2PE也出现了黏结剂对基底失去黏结、与聚乙烯分层的问题。防腐层也出现开裂，导致水渗入失黏防腐层下，产生腐蚀。

      三层聚乙烯防腐层管线在投用几年内也暴露出黏结失效问题，报道介绍，有几条管线的投用时间还不到两年。问题表现出的程度不一，较轻的是防腐层黏结性下降，可以被轻易地剥下，但基底没有受到腐蚀，最严重的是腐蚀层和基底完全分离，金属表面有腐蚀产物形成。但是，问题的原因通常是涂装质量存在问题。在新管线上外观完好的防腐层下甚至也发现了活性腐蚀，但这些3PE防腐层采用了低密度聚乙烯，腐蚀原因可以归结为较高的氧气透过率和透水性；三层防腐层还出现了应力开裂，防腐层开裂的原因也是外防腐层上的小划伤。PE材料的和防腐层老化、失效相关性能包括：1，紫外线老化导致的开裂和脆化。2，应力开裂。3，水和氧的渗透性.