Where we are having twin spring hangers or supports in verical run of piping and the piping is hydrotested with both springs locked, each of these springs hydrotest load should be total load in the piping - not shared, as is the case when springs are not locked.

In ASME B31.1 power piping, each spring hardwares for twin springs in vertical piping are specified with total hydrotest load as per ASME B31.1:2010 121.8.1(C).

If the above is not done, springs should not be locked and separate temporary support should be designed in the vertical piping to protect the springs casings.

Please give your opinions on the above observations.
reg,
sam

In the case of twin spring hangers in vertical run of piping, each spring hanger is designed for 50% of total load as the springs balance the loads unlike rigid supports. However, during hydro-test condition, with each spring hanger in locked position, the springs itself are not in action i.e. being locked they are not subjected to tension or compression.

Its only the spring hardware which will see the load due to piping per hanger during this condition. Regarding the design of the spring hardware, if you refer the catalog you can find the statement "Standard pipe clamps and accessories are designed to withstand an increased short term such as occurs during hydro-test, up to twice the quoted load capacity for the item"

Hence, the spring hardware is designed for twice the quoted load capacity as per vendor catalog.

During spring hanger selection stage you could also select the spring hanger size such that the Hydro-test load is within the load range of the spring hanger (Including overtravel)

You have not answered the query.

It is true that if you do not specify hydrostatic test load, twice the load capacity is considered hydro test load by default.

But, in vertical piping having twin springs, in locked condition, the sub division between two hanger casings are not equal.

We have noticed the bottom lock cutting down the spring casing due to high hydrotest load in one of these two springs which other has not taken load at all in many situations. Had each spring casing and hardwares except the spring coil been designed with total hydrotest load, this could not have happened!

You need to simulate right hydro test conditions in CII model. Also, wisdom of code B31.1:121.8.1(C) is there for your rescue.

reg,
sam

Dear sam,

I would like to highlight the following points related to Hydro-test load

1) Pipe movement expected in lateral and transverse directions are small, the load distribution on either spring hardware of the twin assembly is expected to be equal under normal circumstances unless there are load re-distributions due to weights of inline components not properly accounted for in design.
2) Hydro-test condition is considered as a short-term condition and hence, allows a larger allowable stress in design.

If you refer MSS-SP58 Section 7.7.1.3 2009 Edition, it is stated "When auxiliary stops are required for installation and hydrostatic test purposes, the unit shall be capable of supporting up to 2 times the normal operating load"

Best Regards
Benoy

Hi Sam,

I understand your concern, however you do not give the full picture on the selected support type. There are supports clamped onto vertical pipe with spring hanger on each end (vertical load is taken from the vertical pipe with shear lugs), and the clamp is almost tight, so your claim is correct. Your model shows the clamped location is and full moment connection, therefore one locked spring hanger takes the full load under the slight pipe movement.

There are similar supports with pivoting action at the vertical pipe location, and the load will be shared by two spring hangers in locked/unlocked positions. If you are using this type support you do not have any problem. The solution is in the modeling. Take the spring hanger support location on the pipe center with two spring. This will solve your problem. LISEGA riser supports may give this option. Talk to your local supplier, they may even produce a drawing for your application.

In the previous paragraph; in case the pipe clamp has sufficient clearance with pipe for the pivoting action and the shear keys allow this, use the same method given in the second paragraph. But most of the riser clamps may not give this clearance. Check it out for your case.

Hope it helps.