Combine Hydrotesting of LTCS and Stainless Steel Piping

[artz023]

Hello! Sirs, newbie here..hoping to get advice from the professionals..is it possible to hydrotest different piping materials (LTCS, SS and Alloy 625 piping) at the same time using water with chloride content of less than 50ppm and with corrosion inhibitor? i am aware that it must be separate test due to corrosion but if there are no other way to separate it like no space to put the blind flanges due to large diameter of the pipe and too congested space.

 

[DSB123]

So you mean the "Design" has not incorporated the need to hydrotest!!!!

 

[LittleInch]

Why must there be a separate test? Are all these materials welded one after the other?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

The materials don't care if they are tested together, but can you meet the pressure criteria?
High enough for all and not too high for any?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[artz023]

Thanks for all your reply, the lines were separated with flanges but moving the pipe spools for placing the blind flange is not possible because of large diameter of pipe 36" and limited space as well. The test pressure difference for both materials is 7-bar so i assume no much issue on testing both materials with higher pressure.

 

[artz023]

Sir EdStainless has a point, i review the client specs and found that the test pressure is calculated from flange pressure rating as per Table 2 of Asme B16.5 multiply by 1.5. In this case, the lowest component might be the Stainless steel flange. Now another question is, is it possible to exceed the MAWP of flanges given in Table-2 of Asme B16.5? I also read about the Ceiling Pressure in Annex-B para. B3 of Asme B16.5 i am wondering if the rating of Table-B1 is really the Maximum Allowable Pressure of the flanges and if it is applicable to different materials (CS, SS).

 

[MickMc]

If all the spools are connected together how can the design pressure differ for each material, and 3 different materials which sounds strange to me and I assume they are all in the same service.

All that notwithstanding and it is the same service get your process engineer to define the actual design pressure which may be far below the flange rating of the various materials and with client consent test to 1.5 DP. Otherwise you may have to dismantle the spools and individually 'strength test' them to 1.5 then 'leak test' to 1.1 when reinstalled.

Also I commonly see SS maximum 1 ppm chloride content in client specs.

 

[MickMc]

Sorry typo in previous post it should be 10 ppm.

 

[artz023]

Appreciate your reply Sir MickMc, i will follow your advise to check with process engineer, this is also the first time i encounter this situation. With regards to water ppm, it is specify in client specs that it must be less than 50ppm for 300 series stainless steel piping.

 

[DSB123]

No matter what pressure you decide on make sure you do not exceed the allowable hoop stress allowed by the Code for the material!

 

[weldstan]

Hydrostatic testing of mixed materials piping systems with one test is often done. You must consider the above recommendations in your test.

 

[curtis2004]

artz023,

I think, for 36" pipe limiting item in determining hydro test pressure is pipe wall thickness, not MAWP of flanges.

Curtis

 

[BigInch]

Due to economic concerns, it would be unusual to have a flange limit hydrotest pressure of a long pipeline, but without knowing wall thickness and material details, or the economics, that may or may not be. In a short pipeline, or plant piping of almost any kind, it could just as easily be a flange that limits test pressure. The important thing is that artz023 looks at all components and identifies which one(s) causes any test pressure limitation.

 

[MessyJessy]

The issue is typically with standing water. Low chloride content and corrosion inhibitor help but are not the solution.

Once the test is finished, immediately drain that water and purge/sweep the pipe with Nitrogen.

Get as much of the free-standing water out as possible and get it dry with nitrogen. Check all the low point drains for moisture content. Also if you can, see if you can get a thermal imaging gun and check the pipe to see if it has 'cool spots'. If it does it means there still water there. Occasionally you might get an 'false' reading from moisture that says it is dry when it is really not.

 

[DekDee]

This is an excerpt from the Hydrostatic Testing specification of the largest LNG project in the world. (CS / LTCS / SS / DSS / SDSS)
The EPCM (a USA company) is also one of the biggest players in the world so you can presume their engineers know what they are doing.

3.4 Hydrostatic Test Fluid
3.4.1 The hydrostatic test fluid shall be potable water with a maximum of 30 ppm chlorides
for carbon steel systems and a maximum of 5ppm chlorides for stainless steel systems
(including duplex and super duplex materials) unless a substitute liquid is deemed
necessary.

Obviously combining different systems for this project would require a max of 5ppm chlorides for all piping.
Seems a bit strange artz023 has 50 ppm for all materials ?
Cheers,
Shane

 

[artz023]

Sorry for the late reply, been away for vacation. Thanks for all your reply and inputs. I will consider all your advice, need to reconfirm also the chloride content for SS materials, 50ppm is a bit high. The Designer also having a check for the test pressure of the systems, might be consider the system design and not the flange MAWP.

 

[XL83NL]

Obviously combining different systems for this project would require a max of 5ppm chlorides for all piping.
Seems a bit strange artz023 has 50 ppm for all materials ?

Nah it doesnt. Referring ASME PPC-2 part 5 article 5.1, chapter 6.1, (t)(7):

Test water used for austenitic steel vessels or
piping systems, or for components clad or overlaid with
austenitic stainless steel, should be condensate, demineralized,
or potable quality water with a verified chloride
content of less than 50 ppm.

This contractor for the 'largest LNG project in the world' has perhaps decided to use his super stringent specs like all the major O&G guys do. Often these specs dont make sense anymore on a lot of subjects, incl this one it seems. Max 50 ppm is good enough for SS, so surely for CS. No reason to go to 5 ppm as I see it.