Document: NRC Regulatory Guide
Document ID: 0b9a3243-ab39-402c-9f4b-215c6e4f79ab
Document Type: regulatory_guide
Title: Inservice Inspection of Ungrouted Tendons in Prestressed Concrete Containments (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740007.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.35
CFR Part: 
CFR Title: 

Content:
tendon forces in two or more surveillances of the same tendon or tendons in a group. By extending the trend line, one can determine when the effective tendon force will be below the minimum required. Regulatory Position 7.2 provides a means of tracking elongations during lift-off testing. The 10% tolerance in elongations at specific loads of reten sioned tendons should include the effect of differen tial friction (from fully greased vs. coated tendons) and errors attributed to calibration, measurement procedures, and equipment. Regulatory Position 7.4 provides detailed guid ance on the results of the grease examination. The incident of tendon anchor head failures at Farley demonstrated that the free water in grease was the main source of hydrogen for hydrogen stress cracking of high-hardness anchor heads. High hardness anchor heads are used in large-size tendon systems (i.e., _Ž750 tons). Since the small-size (<_750 tons) tendons have not exhibited such characteristics, two limits for water are provided. It should be recog nized that these limits are not the threshold limits for distress in anchor heads. When these limits are ex ceeded, it is advisable to detension the tendon and look for cracks on the shim side of the anchor heads. An assessment of a base number for filler grease has been proposed for new grease in ASME Sec tion III, Division 2, and for new and old grease in ASME Section XI. The grease used in many operat ing plants tends to have a low base number (_55). The newer grease formulations tend to have base numbers in excess of 20. Hence, two acceptance limits have been provided. At least two plants that implemented the detailed grease examination criteria experienced problems with the void limit of 5%. Further inquiry into the matter revealed that when the injection pressure was very high (twice the pressure used during installation of grease), the amount of grease replaced was 10 to 15% higher than that removed. The staff discourages this practice,