Pay attention to stress corrosion cracking of the small floating head bolts in the heat exchanger
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Be aware of stress corrosion cracking in the small floating head bolts of heat exchangers. Equipment in petrochemical plants is prone to stress corrosion cracking due to the corrosive nature of the process fluids, combined with the stresses generated when the bolts are tightened. The figure below shows the rich gas water cooler in a petrochemical plant, where stress corrosion fracture of the bolts occurred on the process side. Stress corrosion is highly insidious in petrochemical equipment and causes severe damage; therefore, special care must be taken when selecting bolts for design purposes.
In the compression rich gas cooler and liquefied gas cooler of our catalytic unit’s absorption and stabilization system, bolt failure often occurs. In addition to stress corrosion caused by the medium itself, bolt failure is most likely to result from thermal expansion and contraction during the purging operations when the unit is started up or shut down. In addition to using bolts made of suitable materials, special attention must be paid to the purging of heat exchangers.
What material is the bolt made of, and what are the elements sensitive to stress corrosion? Thank you!
The bolt material originally used was 40Cr, with an HB hardness of 317; this hardness is too high and not suitable. The bolt material chosen this time is 30CrMoA, in order to reduce the carbon content and enhance toughness. The HB hardness is 229, a decrease of 88; the processing requirement is that the HB hardness should not exceed 200. As the hardness of the material decreases, its toughness increases, which enhances its resistance to stress corrosion. The actual performance is good.