Requirements for low-temperature impact testing of long-distance pipelines

Toughness should refer to impact testing. The impact test temperature can be determined based on specific application conditions and the standards for selecting steel pipes. For example, the common impact test temperatures for carbon steel and low-alloy steel in China are 0°C, -20°C, and -40°C; for A333 GR6 as specified in ASME, the low-temperature impact test temperature is -46°C... The requirements regarding the impact energy value can also be found in relevant standards, such as those outlined in GB6479.

The impact temperature is based on the design temperature; if the material standards specify temperature limits that meet your requirements, things will be simpler for you.

This standard primarily requires that impact tests be conducted when the ambient temperature or operating temperature during storage, transportation, or construction is below 0°C. If a temperature of -20°C is reached during this process, should the test be carried out at -20°C? Usually, when designing pressure pipelines, we do not take the ambient temperature into account, as these are all conditions of low temperature and low stress. Generally, only the temperature of the medium is considered; I’m not very familiar with the standards for long-distance transmission

I really don’t know this. You can take a look at the answers from above to see what they say; I’m also learning it*

Since the standards require it, it has to be done – are they national standards?

This post was last edited by Liu Jiajia on 2017-2-9 at 17:15. Clause 5.3.4 of GB 50253-2014, the \"Code for Design of Oil Pipeline Engineering\", stipulates that when the ambient temperature or operating temperature during the storage, transportation, and construction of steel pipes is below 0°C, toughness requirements must be imposed on the steel pipes as well as the materials used for pipeline accessories. Is this requirement for toughness the same as the requirement for low-temperature impact testing? So what temperature range is generally used for impact tests? How should the impact energy be determined? 1. Is this toughness requirement the same as that for the low-temperature impact test? First, clarify the concept of resilience. Toughness refers to a material’s ability to absorb plastic deformation work and fracture work before breaking (impact toughness), or it denotes the material’s capacity to resist crack propagation (fracture toughness). The better the toughness, the lower the likelihood of brittle fracture. Impact toughness is commonly expressed by the absorbed impact energy Ak of a standard specimen, which is the value obtained from the impact test. Although the impact absorption energy cannot truly represent the toughness or brittleness of a material (since the energy absorbed in impact tests with notches is not entirely used for the deformation and fracture of the specimen; part of it is consumed in aspects such as the ejection of the specimen, body vibration, air resistance, and friction in the bearings and measuring mechanisms), it is widely used because it is highly sensitive to changes in the internal structure of the material, and the test is simple and easy to conduct. Impact tests are divided into three types based on the test temperature: room temperature, low temperature, and high temperature impact tests. Materials tend to become brittle at low temperatures, a phenomenon known as low-temperature brittleness (the tough-brittle transition temperature tk). Therefore, low-temperature impact tests must be conducted at low temperatures. Therefore, the toughness requirement mentioned in the standards can be fully understood as a requirement for low-temperature impact testing. 2. So what temperature range is generally used for impact tests? As mentioned above regarding the tough-to-brittle transition temperature, there is currently no simple method for determining it; it is usually defined based on changes in energy, plastic deformation, or fracture morphology over time. To this end, impact tests need to be conducted at different temperatures, and curves (such as the impact absorption energy-temperature curve, the curve showing the relationship between the area occupied by various regions in the fracture surface and temperature, and the curve showing the relationship between the amount of plastic deformation after specimen fracture and temperature) are generated based on the test results in order to determine tk. In practical engineering, the design temperature is generally taken as the temperature for low-temperature impact testing. At the same time, factors such as material thickness (note that curve) and the welding process of the welded joint are also taken into account. This is specified in standards such as HG/T 20585-2011 \"Technical Specifications for Steel Low-Temperature Pressure Vessels\" and GB/T 20801-2006 \"Code for Pressure Piping – Industrial Piping – Implementation Guidelines\", among others. HG/T 20585-2011: GB/T 20801-2006: Similar requirements apply to long-distance pipelines as well; for oil pipelines, refer to the explanatory notes in Section 5.3 of the standard GB 50253-2014 \"Code for Design of Oil Pipeline Projects\", which are excerpted as follows: 3. How should the impact energy value be determined? The requirements for impact energy are specified in various standards; for oil pipelines, refer to Appendix G of GB/T 9711-2011 \"Steel pipes for pipeline transportation systems in the petroleum and natural gas industry\" (note that when impact testing is required, the pipeline should be of PSL2 grade). I won’t quote it here.

Thank you for the reply; it’s very comprehensive. May I ask whether, in accordance with the explanatory provisions of Section 5.3.4 of the standard GB 50253-2014 \"Code for Design of Oil Pipeline Engineering\", it can be understood that the low-temperature impact test should be conducted at the lowest temperature encountered during transportation or construction?