Pl. help in coming out of one confusion regarding hydrotest pressure as per UG-99(b) (MAWP basis) & UG-99 (c)(MAP basis -Hyd. Head).

why static head is only subtracted in MAP basis & not on MAWP basis as both basis calculate hydrotest pressure on top?

Consider one case in which corrosion allowance is zero & design temp. is such that the allowables at d/n temp. are same as that of room temp means design temp. is very low as 65 degreee celcius.

in that case both MAWP & MAP will be equal but hydrotest pressure coming out will be different on both basis?

pl. reply....

Dear Mr.Mayank,

UG-98(b) says determination of MAWP of a VESSEL PART, in corroded condition and in the presence of worst combination of UG-22 loadings.

when i am determining MAWP as per above definition of a cylinder (lets say of some height) , MAWP will be at the bottom most point.

Now UG-98(a) is intertested in determination of MAWP of complete VESSEL and by that definition MAWP of top most point is determined.

now lets say there is a dish at the top and lets us consider it is having a lesser MAWP than the cylinder MAWP.

even after subtracting the static head of cylinder the DISH MAWP is still less than that of pressure at cylinder top. Since we dont want to overstress the dish, in this simplest case TOP DISH MAWP may be the deciding factor for VESSEL's MAWP.


Now in your statement you are mentioning MAWP and MAP are same with some conditions.

Please refer below link for more information on why hydrotest based on MAWP and MAP will never be same.

http://www.onetb.com/forum/viewtopic.php?f=4&t=3495


Also as per Appendix-3 definition of calculated test pressure we get MAP of the each vessel part by using design formulas. the various cases for MAP determination are mentioned in above link.

Also as per definition of MAP, we get the maximum working pressure in new condition that is including corrosion allowances.

Regards
ASD23789

Also, while determining hydrotest as per UG-99 (c), the basis (MAP) is multiplied by 1.3 and then reduced by the static head on the element.

Thus the MAP pressure as mentioned earlier is the pressure allowable at the bottom most point in non-corroded condition.

Also when doing hydrotest of a vertical vessel in horizontal condition, we don't add static head of height in horizontal condition, because we already have determined thickness considering the static head.

I would like to make my stand clear.

Refer Cl. UG-99(d), it is stated that "The requirements of UG-99(b) above represent the minimum standard hydrostatic test pressure required by this
Division."

When i am designing a vessel having Corrosion allowance zero and designed at room temp., then MAP = MAWP = 50 Kgf/cm2.
static Head=2

And so the Hydrotest press. calculated based on UG-99(c) [63 Kgf/cm2] is lesser than UG-99(b) [65 Kgf/cm2], because of Static Head deduction. And now the Client spec. wants the vessel to be Hydrotested as per UG-99(c).


Now my confusion is that can i use the same value as per UG-99(c) i.e. 63 Kgf/cm2, or i need to meet minimum requirement of UG-99(b) i.e. 65 Kgf/cm2 based on UG-99(d).

Dear sir,

please refer the definitions of MAWP & MAP given in pressure vessel design manual by Dennis Moss.

Even if your c.a is zero and design stresses are at ambient values, mawp is considered at worst combination of Ug-22 loadings and map is new and cold and no loadings are considered.

Can you please post the pvelite or result file also?

Regards
asd23789