RE: [PipingDesign] HF piping

From: <Sajit>
Date: Thu Oct 21 2004 - 06:07:00 EDT

Wish there was sketch feature in addition to the text posts that one can make. One could scribble sketch something that needs a illustration.

Umesh that will not be the BOP but the inside bottoms should match to allow for the draining. I think it is called in civil parlance as the invert.

-----Original Message-----
From: umesh k.n. [] Sent: Thursday, October 21, 2004 11:12 AM To:
Subject: Re: [PipingDesign] HF piping

Hello Robert,

   Sorry for delay. Tangential connection means Bottom of 1" drain line shall flush with the bottom of larger size piping section from which you are draining. This means BOP of both pipes shall be same. I have a drawing..i will send soon.


Sr. Piping & PDS engineer,
SK Engineering & Const. Ltd., Seoul, SouthKorea.

"C.Y L" <> wrote:

Thanks a lot umesh, what do you mean by " All 1" drain connection shall be tangential to process piping." ? How do I make the drain tangential?


Robert Liu

"umesh k.n." wrote:

Hello Mr. Liu,

>Can you share some experiences with me about Hydrofluoric acid piping design
>please? What should I watch out? Any special requirement besides those in
>common hydrocarbon piping design? The piping spec I'm using now says, " Small
>branch from bigger header has to be from horizontal" why is that?

Basic principles of HF piping design:

q I was involved in the design 2 Alkylation plants in Mexico, both of UOP licence. HF plant is a dangerous plant.

q Piping layout shall be safe from all operation & maintenance point of view.

q Avoid complex piping layouts; avoid congested corridors (for operator movement) and platforms.

q If there are any valves to be regularly accessed, located them at ground levels or in platforms.

q While designing any piping configuration, remember that operator shall always carry a portable breathing apparatus. This means wider access areas & platform areas.

q All vents & drains in HF class piping shall be either routed to flare or u/g drainage system.

q Design the escape ladders, that upon anticipating danger, operating personnel should able to get out of the plant easily & quickly.

Special notes related to piping design:

q Copper tube piping shall be provided at the end of all drain lines leading to Acid Funnel.

q 2Â" above lines shall have ¾Â" vent at all pockets.

q HF acid pumps have Alkylate flush supply & return, Isobutene flush, lines.

q Each acid pump drain shall be flared before pump is removed for maintenance.

q Each pump seal pot vent line shall be separately routed to Flare header.

q Acid unloading line requires special support arrangement (No pocket design)

q Catalyst loading / Unloading type reactors shall require special attention during design stage.

q Portable exhauster connection shall be tangential tap to pipe.

q Each Control valve shall have drain line connected to flare.

q When CV is to be taken out for maintenance, close the isolation valves & Flare the drain first.

q There will be separate emergency Air header in rack to feed emergency booths.

q Drain valve is necessary between high Pr. double b/v for Bleeding

q Breathing air stations shall be located throughout the plant.

q Portable breathing air apparatus shall also located in high risk areas.

q Level gauge, level transmitters vents shall be routed to flare.

q Level gauge, level transmitters drains shall be routed to u/g drain as well as to flare.

Draining procedure in any HF class piping:

q While you are in HF area safety clothing with mask & a portable breathing air apparatus is a must.

q Generally all the drains will have an u/g drainage connection and a flare connection.

q First open the drain valve to u/g acid drainage system.

q Secondly, open the valve in the flare connected line to remove HF gas.

q Thirdly use a portable exhauster to purge any left over HF gas to flare.

HF1- class Piping: (Hot Hydrofluoric acid, Monel class, 300# R.F.)

q Bosses on valve shall not be drilled unless indicated in P&ID.

q If shown in P&ID ¾" Sch 80 pipe nipple shall be shop socket welded to main valve.

q All ¾ " connection to larger lines shall be reinforced by gussets.

q No unions permitted.

q Install bleeder connection in the cavity between two seating surfaces of gate valve.

q All valve and swing check valve Â"GÂ" point drain size shall be ¾ Â" size.

q Ring joint with soft iron ring (or monel ring) is acceptable alternate to R.F. flanges.

q Spiral wound gasket shall have flange surface finish of 125-ra minimum to 250 max.

q Each casting shall meet the hydrostatic test of ASTM A703 requirements.

q All welded piping components shall be post weld heat-treated.

Hf-2 class Piping: (Cold Hydrofluoric acid, Carbon steel, 300# R.F.)

q Minimum line size is 1" except instrumentation connection.

q All 1" drain connection shall be tangential to process piping.

q All bleeders shall be located in horizontal plane.

q Bleeders tapping could be ¾" size.

q All reducers shall be eccentric with flat side down.

q Temperature limit for plug valve 177 c.

HF-1 and 2:

q All valves shall have grease injector threads.

q All pipe girth weld shall be full radiography. (ASME b 31.3 Para 344.5)

HF-4 (Traced HF acid, Carbon steel, 150#RF) & HF-5 (Traced HF acid, Carbon steel, 300# R.F.)

q All pipe girth weld shall be subjected to 10% random radiography. (ASME b 31.3 Para 344.5)

Hf-2, 4, and 5:

q All CS pipe shall have the following chem. Composition: Ni + Cr + Cu < 0.2 wt %

q All welds except socket welds shall have a maximum weld hardness of 200 Brinnel.

q If weld hardness exceeds 200 BHN one hour at a minimum temp. 594 c

q All socket welds shall be liquid Penetrant inspection. (ASME b 31.3 Para 344.4)

Hf-1, 2, 4 and 5:

q No SS gasket or valves.

CAUTION! q HF Acid is extremely dangerous. Follow all industry, local and internal safety procedures when dealing with any valve or valve part that is intended for HF Acid service.

q Before performing any work and/or disassembling any valve, ensure that all pressure has been removed from the line and from any cavities within the valve.

q Prior to commencing with any internal work on HF Acid service valves, ensure that the entire valve has been properly neutralized.

q Hydrofluoric Acid is a highly corrosive acid, which can severely burn skin and eyes. The vapors alone from HF acid can cause severe burns to these tissues. It is therefore of extreme importance that workers familiarize themselves with the specialized Hydrofluoric Acid Safety Guidelines before working with equipment containing, or having contained, hydrofluoric acid.

q HF is a severe skin, eye, and respiratory irritant, which is unusual in that pain may not occur initially upon contact with the acid. Therefore, HF can penetrate deep into tissue without warning, causing delayed pulmonary edema or deep tissue burns requiring immediate medical attention. HF, which penetrates into tissues, may cause slow tissue death, resulting in very undesirable effects, such as the loss of a finger, which came into contact with the acid!

Most of the licencors specify these precautions. Apply them strictly. Give special attentiion to P&ID notes..

Hope this will guide you towards better design,


Umesh K.N.,
Sr. Piping & PDS engineer,
SK Engineering & Const. Ltd., Seoul, SouthKorea.

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