×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

#### Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
To Your Posts
• Keyword Search
• One-Click Access To Your
Favorite Forums
• Automated Signatures
On Your Posts
• Best Of All, It's Free!
• Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

# Blocked in overpressure protection requirement

 Forum Search FAQs Links MVPs

## Blocked in overpressure protection requirement

(OP)
Dear Members,

I have a heat exchanger to heat Natural Gas (tube side) for combustion in 2 drum dryers. LP steam at 350kPa is on shell side. The NG inlet temp is 12 F and outlet is 68 F. I need to know if there is a need for a PSV (thermal case) on the tube side if the NG is blocked in. Most of the literature and API 520/521 refer to need for PSV (thermal case) for "liquids" that are blocked since liquids are incompressible.

### RE: Blocked in overpressure protection requirement

So what do you calculate to be the max possible blocked in pressure on the tubeside, and does this exceed tubeside design pressure. For the calc, use initial conditions for Pi to be max normal op press and 68degF.

Pf = Pi.(460+Ts)/(460+68), where Ts = sat temp for LP steam in degF.

Though the codes speak of overpressure due to liquid expansion, the same would apply to gas also. In any case, there are no exclusion clauses stated in the API for equipment that is gas filled.

### RE: Blocked in overpressure protection requirement

(OP)
Yes, the calculated Pf is above the design pressure of the tube side. Design pressure is 770 psi and Pf is 1000 psi. So this would require a PSV for the thermal case (correct)?
So I have 2 questions:
1. Is the above equation available in API 520/521?
2. How do I size the PSV? Do I calculate the Thermal rate Q, and select appropriate PSV.

### RE: Blocked in overpressure protection requirement

A fire scenario for the tube side may be credible too.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

### RE: Blocked in overpressure protection requirement

If you have access to a process simulator ( Hysis or Simsci - Pro II), you could easily model this blocked in heating scenario for the HX tubeside in the batch depressuring utility. These simulators will also show you the pressure rise profile with time before the RV actuates. The required relief orifice size is obtained by trial and error to maintain tubeside pressure at 770psig. Specify the external heat input to the tubeside to be the design case HX duty appropriate to the 770psig operating region.

The formula provided earlier can be derived from first principles - API521 provides general guidance and philosophies, and some formulas where derivation from first principles is not possible or is too involved.

Agreed, pls read up your company design guidelines on how to evaluate tubeside firecase scenario for the type of HX you have.

### RE: Blocked in overpressure protection requirement

(OP)
Thanks for details. Much Appreciated.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

### Reply To This Thread

#### Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!

#### Resources

3D Scanning in the Automotive Industry
With over 100 years of production history, the automotive industry has been at the forefront of manufacturing technology since its inception. Whether the transformative technology of the day was the assembly line, the integration of robotics into the manufacturing process, or the switch from steel to aluminum frame chasses, the automotive industry has consistently implemented advanced technology into its manufacturing and production workflow to improve manufacturing and product performance. Today, the same is true. Download Now
Green light on lidar: Developing low cost systems for autonomous vehicles
Lidar has been around for quite some time, but to date, it’s been custom—and expensive. Right now, there isn’t a clear-cut solution that’s suitable for all applications, such as lidar in autonomous vehicles. As they explore options, optical and mechanical engineers are forced to make choices and tradeoffs during the design process. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!

Already a member? Close this window and log in.