Hydraulic Pipe Repair

[TugboatEng]

Does anybody know of a no hotwork method of attaching a fitting to a 1" pipe that operates up to 3000 psi? There are numerous products for 1" tube but I'm coming up empty handed for pipe. I have a few lines that keep cracking in the socket weld. I'm assuming they were welded with the pipe bottomed in the fitting.

 

[akkamaan]

Is it 1" (=25.4 mm) tube or 25 mm tube?

 

[TugboatEng]

1" pipe. 1.315" OD.

 

[mk3223]

Some questions:
- What's the Code requirement for the piping system?
- Do the Code and Owner's Standard allow a threaded or mechanical joint for the 3000psi system?

You may want to figure out the actual cause of the weld crack in the "existing(?)" piping, and fix it with the correct and proper action to maintain the mechanical integrity of the high pressure system.

 

[LittleInch]

#3000 screwed fittings?
Eg.

https://www.nero.co.uk/Catalogue/Fittings/High-Pressure-Fittings/3000LB-Pipe-Fittings-NPT

See asme b16.11

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

 

[hydtools]

What LI said.

Ted

 

[TugboatEng]

I could thread it. I am unsure of wall thickness. What is the pressure rating of threaded sch 80? This is for hydraulic steering on a z-drive and sees high cycles.

I believe the cracking is caused by residual stress from welding. It's not common knowledge in the marine industry that socket weld fittings must not be bottomed out prior to welding.

 

[TugboatEng]

 

[LittleInch]

SW is normally prohibited on high cycle service.

I've never liked SW. If you're going to weld it then butt weld it.

Fairly sure sch80 is good enough for 3000 psi screwed fittings.

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

 

[hydtools]

https://www.oilandgaspipingmaterials.com/article/schedule-80-seamless-pipe-pressure-rating.html

https://www.engineersedge.com/fluid_flow/steel-pipe-pressure-ratings.htm

Posted the link because I could not get a good chart copy and paste.

Ted

 

[LittleInch]

For 1" pipe sch 80 is minimum schedule for threaded joints at that size in ASME B31.3.

I stand corrected - table 7 in ASME B 16.11 is interesting. 3000 recommends sch 160 for threaded, but you might be able to use thinner pipe

Pipe Used for Rating Basis [Note (1)]

Designation
of Fitting Type of Fitting Schedule No. Wall Designation

2000 Threaded 80 XS
3000 Threaded 160 . . .
6000 Threaded . . . XXS

3000 Socket-welding 80 XS
6000 Socket-welding 160 . . .
9000 Socket-welding . . . XXS

NOTE:
(1) This Table is not intended to restrict the use of pipe of thinner or thicker wall with
fittings. Pipe actually used may be thinner or thicker in nominal wall than that shown in Table 7.
When thinner pipe is used, its strength may govern the rating. When thicker pipe is used (e.g., for
mechanical strength), the strength of the fitting governs the rating.

I believe your root cause issue is fatigue cracking of the weld. SW fitting are notorious for this when exposed to high cyclic stresses.
But again, for high cycle service threaded joints are usually avoided / not used.
Combined with bottoming out the fitting you're in high failure mode -

https://www.nrc.gov/docs/ML1006/ML100680787.pdf

Is that picture a coupling or a fitting??

This article might be of interest

https://www.researchgate.net/public...ocket_weld_repair_method_Strong_and_effective

Gets you to the next shutdown.

And this

https://link.springer.com/article/10.1007/BF02715165

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

 

[TugboatEng]

Thank you for the detailed response. We're definitely seeing the root cracking described.

The fitting in the picture is an adapter, SW to NPT

It appears the solution is to lay a whole lot of weld bead on it. There are only 6 pipes giving trouble. I believe I can remove them from the vessel to facilitate repair.

 

[LittleInch]

If you can remove them then get them butt welded. All you issues go away.

SW fittings are cheap and nasty. IMHO.

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

 

[mk3223]

For the high fatigue service, may investigate the failure of the cracked welds and to identify for any possible weld defects, piping cleaning issue, improper weld rod material or weld profile, etc., for fabrication correction.

 

[TugboatEng]

I'm a big fan of the compression type fittings such as Viega Megapress. It eliminates a lot of quality control issues though I question their resilience when exposed to the outside environment (type 420 stainless biting rings). I saw there is a crimp on system out now for hydraulic piping but the pressing tool cost rules out any small projects and the fitting cost rules out large projects.

I would just replace the pipe with tubing and use Swagelok but at -20 diameter the Swagelok fitting requires a costly swaging tool.

 

[hydtools]

Look at Parker reusable fittings. Field repairable, no swaging.

Ted

 

[TugboatEng]

I am a big fan of flareless fitting but I see Parker Ferulok only goes to 3/4 inch. The EO and EO-2 fittings go larger but they're... metric. Swagelok requires a tool to pre-set the ferrules on the tube on sizes over 1".

Funny story, these z-drives are Canadian built and typically built using SAE fasteners but someone special ordered them with metric hardware and they are the only metric item in the boat.

 

[TBP]

Could be bottoming-out the pipe in the fitting, but I'd bet that it's vibration that is causing the cracking. We have a large hydraulic press for production and typically if we have had a line break or socket weld/threaded joint crack, it's been vibration that caused it. Some lines had their supports modified, others they just switched to hydraulic hose.

 

[akkamaan]

Parker's Ermeto fitting system is available in stainless. PDF link

Parker seamless steel tubing available in stainless. PDF link

 

[TugboatEng]

I agree. I think the best solution is to switch to metric tubing as it opens up a wide array of compression type fittings options.