PCC-1 Guidelines/ Clarifications This internal note is issued with the purpose to provide criteria for the application of PCC1 Guideline to avoid any misunderstanding regarding various considerations stated in the guideline. ASME VIII Div. 1 – App. S provides explanation on reasons in which PCC-1 was published. Moreover, App. S should be the main reference for all issues related to flanged joint assembly. The main difference between ASME VIII Div.1 - Appendix 2 and PCC-1 is that Appendix 2 gives the method for calculation of flange thickness without any consideration on the whole joint assembly (flange – gasket – bolts), vice versa PCC-1 starts from the calculated flanged joint as per ASME VIII Div.1-Appendix 2 defining a criteria for tightening, considering all aspects related to the components and the mutual effect on each component. This means that the flange calculation must be carried out in accordance with ASME VIII Div. 1, while PCC1 defines the loads to be applied on the bolts, ensuring tightening of the joint. PCC-1 does not require re-designing of flange even when the load applied to the bolts is higher than the allowable design stress (as per ASME II - Part D), see also ASME VIII Div. 1 App. S regarding this matter. Indeed, PCC-1 main objective is to provide actual bolt load required to guarantee bolt tightening, since once the designer defined the load to be applied on the bolts according to ASME VIII Div.1_Appendix 2, due to several reasons (e.g. bolts relaxation, flange rotation, friction of nuts on flange etc.), there is no guarantee about the real load value which is effectively applied to the bolts. Here below some recommendations regarding the parameters to be used for defining the assembly bolt stress according to ASME PCC-1 Appendix O: a) Maximum permissible flange rotation Maximum permissible flange rotation to be selected considering the type of gasket used in the joint. See O-4.1 for reference, however a max. value of 0.8 deg. should be considered. b) Maximum permissible bolt stress See O-4.1 for reference; Saipem criteria is to use a value of 40% YS approx., to avoid damaging of gasket, higher values may be used for Camprofile metallic type gasket. c) Minimum permissible bolt stress See O-4.1 for reference; Saipem criteria is to use a value of 30% YS approx. to maintain gasket compression during operation d) Target assembly gasket stress See O-4.1 for reference; e) Maximum assembly gasket stress See O-4.1 for reference; typical values are 15000 psi for PTFE, or 30000 psi for Camprofile or Spiral Wound; the values are from gasket manufacturer data. f) Minimum gasket seating stress See O-4.1 for reference; typical values are 3600 psi for PTFE, or 4000 psi for Camprofile and 10000 for Spiral Wound; the values are from gasket manufacturer data. h) Minimum gasket operating stress See O-4.1 i) Gasket relaxation fraction See O-4.1 for reference; the data hall be established based on gasket manufacturer data. Without indications default value of 0.7 is acceptable. The above indications need to be checked with equipment vendors and fine-tuned as per gasket manufacturers’ experience, since values provided in API 660 Std._2015 are much higher than proposed values by gasket manufacturers. Regarding JAZAN Pkg. 1 and Pkg. 2 projects, it is necessary to point out that PCC1 Guideline shall be followed as already mentioned in below documents: - Listed in Material Requisition as project requirement - Stated in ASME VIII Div. 1 App. S - Stated in API 660 Std. However, Vendor may decide to ask a waiver and follow a different criteria for bolt tightening. Such criteria shall have the same validity with demonstration that it is internationally recognized as PCC-1. Vendor’s internal criteria will not be acceptable.
