the constant effect spring hanger need adjust at site douring cold or instlation stage because of difference of actual load and claculated load. in Chinese code GB10181, the alowable is +-10%, but Mss-SP 58 is +-6% . So for me, it need re-claclualion the system if difference large than those allowance. What is your idea about this issue? what are the percentage in your practice?

Hello,

In North America, our Codes and Standards require spring hangers/supports to be manufactured such that they are limited to 25 percent variation for "variable supports" and 6 percent variation for "constant supports".

Although most "constant supports" are set for their specified support force at the time of manufacture, they all include a facility for making "adjustments" (plus or minus) to that supporting force in the field. Some American and European manufacturers will include a facility for making adjustment of 10 percent in the field. For other manufacturers, the adjustability may be as much as 300 percent!!

If your company is a member of EPRI, you can get a copy of the training notes for the "webcast" of my training session on "maintenance of power plant pipe support systems". Those notes address making field changes to the supporting forces for constant supports.

Good luck and regards, John.