Minimum Temperature for Hydrotesting 1

[Ryza00]

Hello,

I have been asked by my client to look into the minimum temperature at which we can hydrotest during the winter. The local site standard states a minimum temperature of 7 deg C but we are not sure where this minimum temperature is derived from. Our company hydrotest criteria states a minimum temperature for hydrotesting as 5 deg C, I believe this is stated to avoid any issues with brittle fracture.

Can anyone shed any light on where these minimum temperatures are dervied from?

I have looked at ASME 31.3 but could not find any reference to the minimum temperature for hydrotesting.

I assume there must be some sort of industry code or practise for this since there will be plants all over the world where they will be testing pipelines in low temperatures?

 

[LittleInch]

I suspect that 7 Deg C is a conversion from 45F - in other words a nice nominal distance from freezing ( 40F is probably a bit close to freezing).

The key issue is how accurate you can predict air temperature and what do you do if temperature falls below your min temp - do you clear all lines currently full of water and how do you avoid freezing water in dead legs and small tubing connections. Hence min temps are normally a practical issue of avoiding damage by freezing of water, especially in small bore piping or connections.

Min design temp for materials is usually zero or lower so unless you have particularly brittle material that should not be a particualr issue, but only you know your system.

Don't forget that min volume/max density of water is about 4 C so as temp falls below that pressure could increase before freezing which is different to normal and can cause issues.



My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

The minimum test temperature should be high enough to avoid freezing, should the external temperature drop during the test. There is no code that addresses that particular situation.

Independent events are seldomly independent.

 

[Ryza00]

Thanks for the replies.

If the minimum temperatures is stated to avoid issues with freezing during hydrotesting, out of curiosity, do you know how they manage this in climates where the temperature rarely gets above freezing? I'm thinking of places like Alaska, do they substitute the water for an anti freeze mix for hydrotesting process pipeline?

 

[DekDee]

B31.3
345.2.2 Other Test Requirements
(a) Examination for Leaks. A leak test shall be maintained
for at least 10 min, and all joints and connections
shall be examined for leaks.
(b) Heat Treatment. Leak tests shall be conducted after
any heat treatment has been completed.
(c) Low Test Temperature. The possibility of brittle fracture
shall be considered when conducting leak tests at
metal temperatures near the ductile-brittle transition
temperature.

B31.1
137.1.2 Temperature of Test Medium.
The temperature of the test medium shall be that of the available
source unless otherwise specified by the Owner. The
test pressure shall not be applied until the system and
the pressurizing medium are approximately at the same
temperature. When conducting pressure tests at low
metal temperatures, the possibility of brittle fracture
shall be considered.

ASME VIII Div 1
UG 99 (h)
It is recommended that the metal temperature during
hydrostatic test be maintained at least 30°F (17°C)
above the minimum design metal temperature, but need
not exceed 120°F (48°C), to minimize the risk of brittle
fracture.

Not sure if that helps at all,
Cheers,
DD

 

[brimmer]

We add methanol

 

[BigInch]

Brittle fracture should not be a problem for any kind of CS pipe at 5 to 7 degrees C.

It is interesting to see the +30deg F above min steel design temp recommendation by BPV, but they obviously are not doing uncontrolled environment, outdoor pipe testing.

Independent events are seldomly independent.

 

[StressGuy]

BigInch,

It can be with thick enough steel.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[BigInch]

I'd probably not be using such a thickness.

Independent events are seldomly independent.

 

[ad911001]

If you use a non freezing test media such as a water/glycol mixture, your min test temperature should be governed by your minimum design metal temperature (MDMT) which should be listed in your LDT. This can very greatly depending on the size of pipe, type of fitting, material, schedule, etc.