Hydrotest Temperature As Per UG-99(h)

Dear all,

This refers to UG-99(h),

Where in code recommends to have difference of 17 degree C in hydrotest liquid temperature & MDMT.

Here I would like to know that it is referred as rated MDMT (Calculated using UCS-66 rules) or

Equipment MDMT (which is mentioned on Process datasheet).

Que. 1

I have case wherein my Equipment MDMT is 16 deg.C

I have water in winter condition in the range of 20 to 25 deg C.

Though UG-99(h) is recommendation not mandatory but it client specification requirement.

Shall I have to increase temperature of water to 16 + 17 = 33 Deg C.

Can I consider Rated MDMT here which is in my case is -10 deg c so as per UG-99(h) hydro test liquid temperature = -10 +17= +7 deg C. so I can use water at temp.20 Deg C.

I have referred Non-mandatory appendix L - Example 9 for impact testing in which code considers RATED MDMT.

Que.2

Vendor has advice to reduce MDMT to 0 Deg. C

So Hydro test liquid temp. Will be = 0+17 = 17 Deg.C and we can use water at temp. 20 deg C.

But in this can we stamp original MDMT = 16 Deg C on the name plate or we have to stamp reduced MDMT on name plate.

Que.3

If I have ordered equipment to such country where in ambient temperature is colder than my RATED MDMT.

Does equipment fabrication will be effected like will material become brittle or fail. I know the stresses will not be generated as equipment is not in operating condition (Except shop hydro test condition)

How the ambient condition where equipment is fabricated is considered while desiciding Design temperature.

Or it like that equipment will fail only at MDMT when it is pressurises (Stresses are there).

This may be the reason we stamp MDMT on name plate as MDMT @ MAWP

Please share or views on that.

_________________________

Mitul Patel,

Static Equipment Design Engineer,

L&T Chiyoda Limited